domain: sdv sde

text:
Manon Villeneuve
email: michel.villeneuve65@gmail.com

A Gaertner
email: andreas.gaertner@senckenberg.de

C Kalikone

N Wazi

M Hofmann
email: mandy.hofmann@senckenberg.de

U Linnemann
email: ulf.linnemann@senckenberg.de

A Gärtner

U-Pbages and provenance of detrital zircon from metasedimentary rocks of the nya-ngezie and bugarama groups (dr congo): a key for the evolution of the mesoproterozoic kibaran-burundian orogen in central africa

Keywords: Mesoproterozoic orogen, Kibaran Belt, Central Africa, U-Pb geochronology, detrital zircon, lithostratigraphic correlations, geodynamic models, rift precursor

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The Kibaran Orogen of Central Africa is supposed to have been formed between 1.4 and 1.0 Ga. Therefore, it is among those orogenic belts like the Grenvillian in North America (McLelland et al., 2001) or the Sunsas and Rondonian-San Ignacio in South America [START_REF] Cordani | Crustal evolution of the South American Platform[END_REF], which were involved in the assembly of the Rodinia supercontinent between ca. 1.3 and 0.9 Ga [START_REF] Li | Assembly, configuration, and break-up history of Rodinia: Asynthesis[END_REF]. The Kibaran belts extend from the Katanga region of southeastern Congo to Uganda through the Kivu province of eastern Congo, Burundi and Rwanda (fig. 1a).

Despite numerous geological studies and radiometric age determinations in Katanga [START_REF] Cahen | Géologie du Congo belge[END_REF][START_REF] Cahen | The geochronology of Equatorial Africa[END_REF][START_REF] Cahen | The Geochronology and Evolution of Africa[END_REF][START_REF] Kampunzu | Assembly and break-up of Rodinia. No link with Gondwana assembly[END_REF][START_REF] Kokonyangi | Geological evolution of the Kibarides belt, Mitwaba, Democratic Republic of Congo, Central Africa[END_REF], in Kivu [START_REF] Boutakoff | Géologie des territoires situés à l'Ouest et au Nord-Ouest du fossé tectonique du Kivu[END_REF][START_REF] Safianikoff | Les systèmes de l'Urundi et de la Ruzizi au Kivu et les intrusions granitiques[END_REF][START_REF] Peeters | Contribution à la géologie des terrains anciens du Rwanda-Urundi et Kivu[END_REF][START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF][START_REF] Villeneuve | Apports de l'imagerie spatiale à la résolution des structures géologiques en zone équatoriale: exemples du Précambrien au Kivu (Congo Oriental)[END_REF], in Rwanda and Burundi [START_REF] Gérards | Grands traits de la géologie du Rwanda, différents types de roches granitiques et premières données sur l'âge de ces roches[END_REF]Lavreau and Liégeois, 1982;[START_REF] Klerkx | Granitoides Kibariens précoces et tectonique tengentielle au Burundi: magmatisme bimodal lié à la distension crustale[END_REF][START_REF] Tack | Late Kibaran magmatism in Burundi[END_REF][START_REF] Tack | Kibaran A-type granitoids and mafic rocks generated by to mantle sources in a late orogenic setting (Burundi)[END_REF][START_REF] Fernandez-Alonso | Airborne geophysics and geochemistry provide new insights in the intercontinental evolution of the Mesoproterozoic Kibaran belt (Central Africa)[END_REF][START_REF] Deblond | The Malagarasi supergroup of SE Burundi and its correlative Bukoban supergroup of NW Tanzania: Neo-and Mesoproterozoic chronostratigraphic constraint from Ar-Ar ages on mafic intrusive rocks[END_REF][START_REF] Brinckmann | La géologie et la minéralisation primaire de l'Or de la chaine Kibarienne, Nord-Ouest du Burundi, Afrique orientale[END_REF][START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF][START_REF] Fernandez-Alonso | The Mesoproterozic Karagwe-Ankole belt (formerly the NE Kibara belt): The result of prolonged extensional intracratonic basin development punctuated by two short-lived farfield compressional events[END_REF], in NW Tanzania [START_REF] Ikungura | Geochronology and chemical evolution of granitic rocks, NE Kibaran (Karagwe-Ankolean) belt, NW Tanzania[END_REF][START_REF] Ikungura | 40 Ar/ 39 Ar dating of micas from granites of NE Kibaran belt (Karagwe-Ankolean), NW Tanzania[END_REF][START_REF] Boniface | Mesoproterozoic high-grade metamorphism in pelitic rocks of the northwestern Ubendian belt: implications for the extension of the Kibaran intra-continental basins to Tanzania[END_REF], and in Uganda [START_REF] Vernon-Chamberlain | Age and isotope studies on the "arena" granites of SW Uganda[END_REF][START_REF] Buchwaldt | Crustal age domains in the Kibaran belt of SW Uganda: Combined zircon geochronology and Sm-Nd isotopic investigation[END_REF][START_REF] Link | Continuous cratonic crust between the Congo and Tanzania blocks in western Uganda[END_REF], there are important debates concerning the Kibaran belts evolution. This applies particularly for geologists who worked in the western countries, e.g. the D.R. Congo, and those who worked in eastern countries like Burundi, Rwanda, and Uganda.

One debate concerns the number and timing of tectonic events. For Kampunzu et al. (1998a) as well as for [START_REF] Villeneuve | Les sillons plissés du Brundien supérieur dans la chaine Kibarienne d'Afrique centrale[END_REF], there are three main tectonic events accompanied by granitic intrusions around 1380, 1250 and from 1100 to 1000 Ma. Other authors propose a termination of the Kibaran Orogen at around 1.26 Ga [START_REF] Rumvegeri | Le Précambrien de l'Ouest du lac Kivu (Zaire) et sa place dans l'évolution Géodynamique de l'Afrique centrale et orientale[END_REF][START_REF] Rumvegeri | Le Précambrien de l'Ouest du lac Kivu (Zaïre) et sa place dans l'évolution géodynamique de l'Afrique centrale et orientale[END_REF], 1.25 Ga [START_REF] Pöhl | Metallogeny of the northeastern Kibara belt, central Africa-recent perspectives[END_REF][START_REF] Brinckmann | La géologie et la minéralisation primaire de l'Or de la chaine Kibarienne, Nord-Ouest du Burundi, Afrique orientale[END_REF], or 1.20 Ga [START_REF] Pöhl | Kibaran evolution and metallogeny of Central Africa: A synthesis at the end of the IGCP project 255[END_REF]. However, there is a general agreement about a post tectonic intrusive event, characterised by granitoids bearing cassiterite, wolframite, columbo-tantalite, and rare earth minerals, between 1.0 Ga and 0.94 Ga [START_REF] Caron | Les ressources minérales d'âge protérozoïque moyen en Afrique équatoriale et l'évolution géodynamique de la chaine Kibarienne[END_REF].

A second debate concerns the geodynamic interpretation. [START_REF] Kampunzu | Les Kibarides d'Afrique centrale et orientale: une chaine de collision[END_REF], [START_REF] Rumvegeri | Le Précambrien de l'Ouest du lac Kivu (Zaïre) et sa place dans l'évolution géodynamique de l'Afrique centrale et orientale[END_REF] and [START_REF] Debruyne | Regional geodynamic context for the Mesoproterozoic Kibara belt (KIB) and the Karagwe-Ankole belt: Evidence from geochemistry and Isotopes in the KIB[END_REF], who worked in the southern and western areas of the orogen (DRC), favoured a classical subduction / collisional model, while [START_REF] Klerkx | Granitoides Kibariens précoces et tectonique tengentielle au Burundi: magmatisme bimodal lié à la distension crustale[END_REF], [START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF][START_REF] Fernandez-Alonso | The Mesoproterozic Karagwe-Ankole belt (formerly the NE Kibara belt): The result of prolonged extensional intracratonic basin development punctuated by two short-lived farfield compressional events[END_REF], who worked in the eastern areas (Rwanda and Burundi), favoured an extensional basinal model.

A third debate concerns the age of the Kibara Belt's basement. In the Nya-Ngezie area, it was first ascribed to the Ruzizian Group, which supposedly occurred coeval to the Eburnean Orogeny at ca. 2.0 Ga (figs. 1 and 2; [START_REF] Boutakoff | Géologie des territoires situés à l'Ouest et au Nord-Ouest du fossé tectonique du Kivu[END_REF][START_REF] Safianikoff | Les systèmes de l'Urundi et de la Ruzizi au Kivu et les intrusions granitiques[END_REF]. More recent studies limited the area of the Ruzizian outcrops drastically. However, [START_REF] Lavreau | Le groupe de la Ruzizi (Ruzizien du Zaïre, Rwanda et Burundi) à la lumière des connaissances actuelles[END_REF] revealed the presence of Palaeoproterozoic Ruzizian terranes in the Lower Burundian (Kibaran) granitised basement. [START_REF] Villeneuve | Les sillons plissés du Brundien supérieur dans la chaine Kibarienne d'Afrique centrale[END_REF] considered a single basement in the northern part of the belt, where the Ruzizian and the Lower Burundian system with granitoid intrusions around 1375 Ma cannot be differentiated. These rocks are covered by several sedimentary formations that were folded and metamorphosed prior to the emplacement of 1.0 to 0.9 Ga old tin bearing granitoids [START_REF] Cahen | Rubidium-Strontium geochronology of some granitic rocks from the Kibaran belt (central Katanga, Republique of Congo)[END_REF][START_REF] Cahen | The Geochronology and Evolution of Africa[END_REF].

The process of putting the Kibaran Orogeny in a global context resulted in numerous proposals for stratigraphic correlations. This applies particularly for correlations between the southern Kibaride Belt (KIB), the northern Kivu (KVB), and Karagwe Ankolean (KAB) belts that are separated by the SE-NE striking Ubendian-Ruzizian high. Contemporary authors [START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF][START_REF] Fernandez-Alonso | The Mesoproterozic Karagwe-Ankole belt (formerly the NE Kibara belt): The result of prolonged extensional intracratonic basin development punctuated by two short-lived farfield compressional events[END_REF] conclude that the northeastern part of the Kibaran orogens is different from the southern part. They proposed to distinguish the KIB in southern Katanga (former Shaba) from the KAB in Burundi, Rwanda, and Uganda. The complexity of the northwestern part of the Kibaran orogens, corresponding to the Kivu province of Congo, justifies a differentiation of the KVB from the KAB. This approach considers the fact that there is no continuity in the field, no stratigraphic land mark level, and no sufficient radiometric age data to propose consistent correlations between the KAB and KVB that are separated by sediments and lavas of the "East African Rift". The closest area between them is Nya-Ngezie, which is separated from the adjacent countries of Rwanda and Burundi by the Ruzizi River. This area was carefully studied by [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF].

In order to clarify the above-mentioned debates U-Pb age determinations on detrital zircon have been performed on six samples from the Nya-Ngezie area south of the Kivu Lake (figs. 1 and2). This area has formerly been used as referential stratigraphic scale for the Burundian formations, which there are capped by the pan-African "Itombwe" trench [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF]Cahen et al., 1979;[START_REF] Villeneuve | Géologie du synclinal de l'Itombwe (Zaïre Oriental) et le problème de l'existence d'un sillon plissé pan-africain[END_REF]. The new results suggest two latest Kibaran-Burundian depositional events of siliciclastic sediments younger than 1250 Ma, which were subsequently tectonised around or after 1111 ± 38 Ma. Finally, the existence of a Ruzizian "ghost" basement can be proposed for the vicinity. (Villeneuve and Chorowicz, 2004, modified) shows a schematic map of the northern part of the Kibaran belts (KVB and KAB). Several sedimentary belts, indicated by green colour, have a N-S general trend, while only few are E-W. Most of them are resting upon metamorphic basement inliers (yellow colour). According to [START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF], the eastern part contains two domains: An eastern domain (ED) comprising sedimentary deposits on top of an Archaean basement, limited to the east of Rwanda and Burundi, and a western domain (WD) with sedimentary basins deposited on top of metamorphic inliers older than 1375 Ma [START_REF] Tack | Kibaran A-type granitoids and mafic rocks generated by to mantle sources in a late orogenic setting (Burundi)[END_REF]. Both domains are separated by a narrow transition zone (TZ, [START_REF] Tahon | New insights about the evolution of the Mesoproterozoic Northeastern Kibarabn belt (Central Africa)[END_REF], including mafic to ultramafic sills of the Kabanga-Muzingati intrusive province (KM). A-type granitoid magmatism was found in two sites in the Gitega-Makebuko-Bukiasari (GMB) alignment of central Burundi that occurs in close spatial association with some KM mafic / ultramafic complexes and the TZ. However, emplacement ages of the KM complexes and A-type granitoid massifs of the GMB alignment seem not to be coeval.

Regional geological setting and previous geochronological framework

In the northern Kibaran belts (KVB and KAB).

A N-S-elongated structure (in blue colour) cropping out west of the Kivu Lake, is ascribed to the pan-African orogen [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF]Cahen et al., 1979).

These belts are bound to the east and to the north, by the Neoarchaean Tanzanian Craton and Kibalian Shield (3.0 to 2.5 Ga), themselves covered by Late Proterozoic sediments. To the south they are bound by the ca. 2.0 Ga Ubendian and Ruzizian belts. The KVB was first covered by the Palaeozoic sediments of the Karoo Group and then by Mesozoic sediments of the Congo Basin. Cenozoic sediments and volcanic lavas related to the "East African Rift" are limited to the central area separating the KVB from the KAB. Since the beginning of the twentieth century, two main units have been distinguished in the KVB and KAB by [START_REF] Salée | Constitution géologique du Ruanda oriental[END_REF] and [START_REF] Salée | Carte géologique de la région du Kivu, au 500.000[END_REF]: the metamorphic Ruzizian basement, and the overlying metasedimentary Urundian (former name of Burundian) formations. The latter authors provide the first geological map and also the first lithostratigraphic scale of these countries. In this scale the Urundian was divided into three formations, which are from base to top: U1, U2 and U3. U1 is mainly made of shale or micaschist, U2 comprises mostly quartzites, and U3 is again dominated by shale. This trilogy has been used and sometimes abused by successors, which were unable to distinguish common shale and quartzite alternations from the very Urundian trilogy. [START_REF] Boutakoff | Géologie des territoires situés à l'Ouest et au Nord-Ouest du fossé tectonique du Kivu[END_REF] and successors [START_REF] Safianikoff | Les systèmes de l'Urundi et de la Ruzizi au Kivu et les intrusions granitiques[END_REF][START_REF] Cahen | Géologie du Congo belge[END_REF][START_REF] Peeters | Contribution à la géologie des terrains anciens du Rwanda-Urundi et Kivu[END_REF] ascribed the basement inliers to the Palaeoproterozoic. In the KAB of Rwanda and Burundi, most of the granitic intrusions display early Mesoproterozoic ages (Lavreau and Liégeois, 1982;[START_REF] Cahen | The Geochronology and Evolution of Africa[END_REF][START_REF] Klerkx | Granitoides Kibariens précoces et tectonique tengentielle au Burundi: magmatisme bimodal lié à la distension crustale[END_REF][START_REF] Klerkx | Crustal Evolution of the Northern Kibaran Belt, eastern and central Africa[END_REF][START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF]. Four groups of granitic episodes can be distinguished: G1 (1370 ± 25 Ma), G2 (1308 ± 25 to ~1250 Ma), G3 (1094 ± 50 Ma), and G4 (977 ± 18 Ma). Furthermore, [START_REF] Klerkx | Granitoides Kibariens précoces et tectonique tengentielle au Burundi: magmatisme bimodal lié à la distension crustale[END_REF][START_REF] Klerkx | Crustal Evolution of the Northern Kibaran Belt, eastern and central Africa[END_REF] reported an Rb/Sr isochron age of 1185 ± 59 Ma for some granitoids exposed in Burundi and Lavreau and Liégeois (1982) reported a tectono-metamorphic event at 1111 ± 38 Ma. The latter is likely linked to the NW-SE (D2) tectonic phase in central Rwanda.

Several attempts have been performed to establish a synthetic lithostratigraphic succession as well in Rwanda [START_REF] Baudet | Lithostratigraphie du domaine sédimentaire de la chaine Kibarienne au Rwanda[END_REF] as in Burundi [START_REF] Radulescu | Carte géologique et esquisse metallogénique du Burundi[END_REF], and even in the Kivu area [START_REF] Villeneuve | Les sillons plissés du Brundien supérieur dans la chaine Kibarienne d'Afrique centrale[END_REF]. The most used succession in Rwanda and Burundi is that of [START_REF] Baudet | Lithostratigraphie du domaine sédimentaire de la chaine Kibarienne au Rwanda[END_REF], which distinguished four lithostratigraphic groups. However, radiometric ages [START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF] led to the distinction of the ED comprising two groups from the WD with four groups.

2.2

First geologic investigations in the Kivu Belt (KVB) were undertaken by mining companies and the Geological Survey of Congo Belge (SGCB). They distinguished between two main units: the Ruzizian and the Urundian based on their grade of metamorphism. At this time, no consistent discontinuities were found between them. Later on [START_REF] Lhoest | Une coupe remarquable des couches de base de l'Urundi dans l'Itombwe[END_REF], who mapped the Itombwe syncline in the Luemba area of southern Kivu, evidenced an Urundian -now Burundian -syncline superimposed to a Ruzizian basement. [START_REF] Lhoest | Précisions sur la stratigraphie des couches de base du systeme de l'Urundi dans la partie Nord du synclinal de l'Itombwe[END_REF] extended the eastern flank of this syncline to the Nya-Ngezie area, while [START_REF] Peeters | Contribution à la géologie des terrains anciens du Rwanda-Urundi et Kivu[END_REF] did not found any unconformity at all and extended the Itombwe formations until Rwanda. Initially, the N-S trending Itombwe Syncline at Luemba [START_REF] Lhoest | Une coupe remarquable des couches de base de l'Urundi dans l'Itombwe[END_REF], was linked to the Mesoproterozoic Urundian. Then, [START_REF] Villeneuve | Géologie du synclinal de l'Itombwe (Zaïre Oriental) et le problème de l'existence d'un sillon plissé pan-africain[END_REF] showed that there are two different superimposed synclines of which the lower one is linked to a Kibaran, whereas the upper one is linked to a pan-African trench. Consequently, the western unconformity observed by [START_REF] Lhoest | Précisions sur la stratigraphie des couches de base du systeme de l'Urundi dans la partie Nord du synclinal de l'Itombwe[END_REF] at Kasika on the northwestern part of the Itombwe Syncline is not similar to that observed by [START_REF] Villeneuve | Mise en évidence d'une discordance angulaire majeure dans les terrains précambriens du Nord du synclinal de l'Itombwe (région du Kivu, République du Zaïre)[END_REF] at Nya Kasiba on its northeastern side. The first one is related to the base of the Mesoproterozoic Burundian terranes, while the second one is linked to the base of the pan-African Itombwe Group. In order to avoid any further confusion, the upper likely pan-African structure is considered as "Itombwe Syncline" in the following text, while the lower one is named "Luemba Syncline" [START_REF] Villeneuve | Les sillons plissés du Brundien supérieur dans la chaine Kibarienne d'Afrique centrale[END_REF]. The northwestern Kivu area from the Mt. Kahusi to Walikale was initially investigated by [START_REF] Blaise | Géologie des terrains situés au Nord-Ouest du lac Kivu[END_REF] and [START_REF] Boutakoff | Géologie des territoires situés à l'Ouest et au Nord-Ouest du fossé tectonique du Kivu[END_REF], who applied the [START_REF] Salée | Constitution géologique du Ruanda oriental[END_REF] lithostratigraphy. More recent work on that area was published by [START_REF] Kampunzu | Le magmatisme du massif du Kahuzi (Kivu, Zaïre). Structure, pétrologie, signification et implication géodynamique[END_REF], [START_REF] Rumvegeri | Lithostratigraphie et evolution structurale de la chaine Kibarienne à l'Ouest du lac Kivu (Zaire)[END_REF], [START_REF] Rumvegeri | Le Précambrien de l'Ouest du lac Kivu (Zaire) et sa place dans l'évolution Géodynamique de l'Afrique centrale et orientale[END_REF][START_REF] Mugaruka-Bibentyo | Petrographie et geochimie des gneiss kibariens à Bunyakiri, sud Kivu, R.D. Congo[END_REF]. The western edge of the Kivu Lake has been studied by [START_REF] Pasteels | Géologie et pétrographie de la région de Kirotshe (Kivu)[END_REF], [START_REF] Blès | Etude photo-interprétative et reconnaissance géologique et structurale de la zone exclusive de recherches Masisi-Saké[END_REF] and Villeneuve (1983a), who ascribed the metasedimentary formations to the early Burundian Group (Stenian), except a syncline filled with pink shale and feldspathic sandstone linked to the late Burundian [START_REF] Blès | Etude photo-interprétative et reconnaissance géologique et structurale de la zone exclusive de recherches Masisi-Saké[END_REF]. The northern Kivu area was studied by [START_REF] Legraye | Le complexe cristallophyllien et les formations du Kibali de la province Nord-Orientale du Congo-Belge, leurs relations avec les formations comparables des régions voisines[END_REF], [START_REF] Lhoest | Quelques grandes lignes de la Géologie de la concession Nord de la Compagnie Minière des Grands lacs Africains[END_REF], [START_REF] Aguillaume | Géologie du degré carré Lutunguru. Mission Nord-Kivu, 3 eme campagne 1974[END_REF][START_REF] Thibault | Carte géologique au 1/500 000 du Haut Zaïre et du Nord Kivu[END_REF]. The Burundian sedimentary succession was proven in two trenches with a detrital formation at the base and a volcanic complex on top. Tectonic structures are E-W and N-S.

Previous studies carried out by [START_REF] Cahen | Réunion de travail des 1, 2 et 3 septembre 1975: La géologie des terrains précambriens voisins du fossé tectonique occidental, spécialement dans les régions sises de part et d'autre de la partie sud du lac Kivu et du nord du lac Tanganyika, au Kivu, au Rwanda et au Burundi[END_REF] have detected an N-S folding trend prior to the E-W structuration.

The last paper devoted to the KVB [START_REF] Villeneuve | Apports de l'imagerie spatiale à la résolution des structures géologiques en zone équatoriale: exemples du Précambrien au Kivu (Congo Oriental)[END_REF] uses support of remote sensing and led to the recognition of two formations in the basement: a metamorphic one at the base and several metasedimentary formations on top that are named the "Oso Formation" to the north (Masisi area) and the "Ulindi Formation" to the south (Mulungu area). This is in accordance with the results published by [START_REF] Rumvegeri | Le Précambrien de l'Ouest du lac Kivu (Zaire) et sa place dans l'évolution Géodynamique de l'Afrique centrale et orientale[END_REF] in the western Kivu area. Unfortunately, there is no radiometric age data at all on this basement.

The latest attempt to correlate the KVB and KAB [START_REF] Villeneuve | Les sillons plissés du Brundien supérieur dans la chaine Kibarienne d'Afrique centrale[END_REF] took the similarities in local lithologic successions into account, but the lack of "marker levels" like basal conglomerates associated to unconformities prevent any robust correlations and the paucity of radiometric data in the Kivu area is a major problem. The first radiometric ages were obtained by [START_REF] Monteyne-Poulaert | Age des minéralisations pegmatitiques et filoniennes du Kivu méridional (Congo oriental). Indications préliminaires sur les âges des phases pegmatitiques successives[END_REF] and Cahen and Ledent (1979) by the Rb/Sr method (520 ± 9

Ma and 989 ± 28 Ma, respectively). U-Pb data on detrital zircon from metasediments performed by R. Armstrong (Kampunzu et al., 2003a and[START_REF] Kampunzu | Geology and detrital zircons from the Precambrian Itombwe supergroup (Congo): implications for the depositional age, provenance and the geotectonic evolution of the East African orogen during East-West Gondwana continental collision[END_REF] have not yet been published owing to the sudden death of A.B. Kampunzu, in 2004.

2.3

The Nya-Ngezie area is a key area of the Kivu geology and was first studied by [START_REF] Boutakoff | Géologie des territoires situés à l'Ouest et au Nord-Ouest du fossé tectonique du Kivu[END_REF]. He ascribed the western epimetamorphic rocks to the Mesoproterozoic Burundian Group (e.g. Kibaran Orogen) and the eastern metamorphic rocks to the Palaeoproterozoic Ruzizian system (e.g. Ubendian Belt) by reference to the local Ruzizi River. [START_REF] Peeters | Contribution à la géologie des terrains anciens du Rwanda-Urundi et Kivu[END_REF] interpreted this terrain as a monoclinal succession with a moderate dip of 45° to the NE. This led to the hypothesis that the western epimetamorphic rocks are older than the eastern micashists and gneisses. Our own studies in this area show the existence of an unconformity along the eastern edge of the Itombwe Syncline [START_REF] Villeneuve | Mise en évidence d'une discordance angulaire majeure dans les terrains précambriens du Nord du synclinal de l'Itombwe (région du Kivu, République du Zaïre)[END_REF] and differ from the preceding interpretation of the basement. This basement is considered to contain two superimposed lithostratigraphic groups: the upper episedimentary Nya-Ngezie Group and the lower metamorphic Bugarama Group. The first one exhibits large, NW-SE trending structures, whereas the second one shows some E-W trending structures. Both are cross-cut by the N-S Itombwe Syncline. Correlations with the adjacent Rwanda area [START_REF] Frautschi | Feuille Cyangugu. Rapp. Année[END_REF] led us to the ascription of these two basement formations to the Burundian Group. Consequently, we concluded that the stratigraphic formations in the overlying Itombwe structures were Neoproterozoic to Cambrian in age (710 and 520 Ma, [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF]. This hypothesis was further supported by geochronologic investigations (Cahen et al., 1979;[START_REF] Kampunzu | Geology and detrital zircons from the Precambrian Itombwe supergroup (Congo): implications for the depositional age, provenance and the geotectonic evolution of the East African orogen during East-West Gondwana continental collision[END_REF]. Owing to a general lack of radiometric data in the Nya-Ngezie area, the more regional correlations remained very speculative.

The geological scheme reported in figure 2 shows three main structural units, which are from the west to the east: the N-S trending unit (in yellow) corresponding to the "Itombwe Supergroup", the central NW-SE trending anticlines and synclines (in orange) corresponding to the Nya-Ngezie Group, and the NW-SE trending structures (in dark brown) corresponding to the Bugarama Group. The Neogene lavas of the African Rift are lying to the north. Thus, from the top to the base, four main units have been distinguished above the basement in this area:

-The modern alluvium and Neogene lavas consisting of basalts, basanites, hawaiites, and phonolites, studied by [START_REF] Pasteels | Timing of the volcanism of the southern Kivu province: implications for the evolution of the western branch of the East African Rift system[END_REF], Kampunzu et al. (1998b) and [START_REF] Pouclet | The Cenozoic volcanism in the Kivu rift: assessment of the tectonic setting, geochemistry and geochronology of the volcanic activity in the south Kivu and Virunga regions[END_REF].

-The Itombwe Formation of Neoproterozoic-Cambrian age [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF][START_REF] Villeneuve | Géologie du synclinal de l'Itombwe (Zaïre Oriental) et le problème de l'existence d'un sillon plissé pan-africain[END_REF].

-The Nya-Ngezie Group, which is made of rocks displaying a very low grade of metamorphism [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF].

-The Bugarama Group, which includes three formations [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF].

-A granitic pre-Bugarama basement is reported to the south of Kamanyola, but was not studied.

Two unconformities are separating these groups: the "Nya-Kasiba unconformity" between the Itombwe Formation and the underlying groups and the "Mount Kamashuli unconformity" between the Nya-Ngezie and Bugarama groups (Fig. 2).

The Itombwe Supergroup consists of conglomerate and schist at the base and mixtite and schist at the top. Rb/Sr age determinations on these sediments allowed Cahen et al. (1979) and [START_REF] Villeneuve | Géologie du synclinal de l'Itombwe (Zaïre Oriental) et le problème de l'existence d'un sillon plissé pan-africain[END_REF] to ascribe these formations to the Neoproterozoic pan-African Orogen of Katanga. Detrital zircon grains from the basal conglomerate indicate a ca. 710 Ma maximum age of sedimentation [START_REF] Kampunzu | Geology and detrital zircons from the Precambrian Itombwe supergroup (Congo): implications for the depositional age, provenance and the geotectonic evolution of the East African orogen during East-West Gondwana continental collision[END_REF]. The Itombwe Syncline was affected by only one tectonic event (D3), which caused the formation of N-S trending folds with a vertical axial schistosity (S3). [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF] divided this group in two formations: Nya Kasiba at the base and Tshibangu on the top. Only the latter exhibits several mixtite levels.

The Nya-Ngezie Group includes three formations, which are from the base to the top:

-The Bangwe Formation (600 m), which contains two quartzitic members separated by a phyllitic member. They display numerous sedimentary features as cross-beddings, ripple and scour-marks.

-The Mukubio Formation (1345 m) comprises quartzite, conglomerate, phyllite and quartzphyllite. Banded, bicoloured millimetre-thick bedding is characteristic for the phyllites.

-The Mughera Formation (1000 m) consists of ferruginous sandstone (banded iron formations) with cross-bedding, monogenic conglomerate and banded phyllite. Intercalated "black sand" type sandstone beds were interpreted to be the product of sedimentary processes acting in an increasingly littoral environment [START_REF] Chauvel | Les quartzites ferrugineux rubanés du Précambrien du bassin de la Luzinzi (Zaïre): un dépôt de placer à titane, fer et zirconium[END_REF]. These rocks were affected by two tectonic events, termed D2 and D'2. D2 provides the main NW-SE trending succession of kilometric synclines and anticlines shown in the geological scheme (Fig. 2a). These deformations are represented at various scales varying from outcrops to thin sections. Axial planes of the NW-SE folds have a strong dip to the north (60° to 70°). Thus, the northern flanks are reverse, while the southern flanks are in "normal" position. These D2 deformation features represent the main structures in the underlying Bugarama Group. Additional D1 folds are observed in the folds of the lower Bugarama Group, but are absent in the Nya-Ngezie Group. D'2 deformations consist of numerous NE dipping reverse faults with a NE dip parallel to the axial plane of the D2 folds. These D'2 faults are visible at various scales, and are likely the result of south-westward thrusting events. Obviously, the D'2 event is considered as being associated with the last stage of the D2 tectonic event. D2 and D'2 deformations were not yet registered in the overlying Itombwe Group. On the contrary, the D3 folding of the Itombwe Group has been evidenced at various scales, in the Nya-Ngezie and Bugarama groups. D2, D'2 and D3 interferences are discussed in detail by [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF]. In conclusion the D2 and D'2 tectonic events took place after the deposition of the Nya-Ngezie Group and prior to the deposition of the Itombwe Group.

Two metamorphic parageneses have been found in these rocks. They are related to the tectonic cleavages resulting from D2 and D3. Minerals are quartz, biotite, muscovite, and sericite, indicating a medium grade metamorphism.

According to [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF], the Bugarama and Nya-Ngezie groups have distinct sedimentary environments. The siliciclastic Nya-Ngezie Group is made of conglomeratic lenses embedded in coarse sandstone layers. These sandstones show abundant traces of streaming on the bedding surface, such as ripple-and scour-marks, cross-bedding, channel structures, etc. These sedimentary traces are considered as characteristic of a littoral sedimentary environment. "Black sands" in the Mughera Formation, interpreted as beach placers by [START_REF] Chauvel | Les quartzites ferrugineux rubanés du Précambrien du bassin de la Luzinzi (Zaïre): un dépôt de placer à titane, fer et zirconium[END_REF], favour this hypothesis. Fig. 3 presents the direction measured for 80 ripple and scour marks of the Nya-Ngezie Group in their initial position before the D2 and D'2 tectonic deformations. Ripple marks are oriented NW-SE and WSW-ENE, while scour marks are perpendicular to the ripple marks. The scours indicate that the streams either came from the north or from the south. These data suggest that the siliciclastics of the Nya-Ngezie Group are made of immature sedimentary rocks that were most probably formed during the erosion of a belt.

Conglomerates in the Nya-Ngezie Group include clasts, which were probably derived from the underlying Bugarama Group.

The Bugarama Group chiefly consists of metamorphic rocks, such as: phyllite, quartz-phyllite, micaschist, amphibolite, and gneiss. The Bugarama Group has been divided into three formations [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF][START_REF] Villeneuve | La stratigraphie du Précambrien du sud du Lac Kivu (Zaïre oriental)[END_REF], which are from the top to the base:

-The Mushenie Formation (1500 m) consists of quartz-phyllite with conglomerate, biotite-schist and brecciated quartzite with ferruginous matrix.

-The Kamanyola Formation (2300 m) is composed of interbedded grey to greenish metapelite with biotitic quartzite, garnet-micaschist, phyllite, and quartz-phyllite with numerous intercalated amphibolitic sills.

-The Kashenie Formation (> 225 m visible) is made of micaschist with garnet, biotite and magnetite, and calc-silicates.

Rocks of the Kamanyola and Kashenie formations experienced two important folding events. The first folds (D1) are visible in metric outcrops or in thin section (associated to a S1 cleavage), while the second folding (D2) is expressed on the map and corresponds to the NW-SE metric and kilometric structures. D2 is also present in the Nya-Ngezie Group. However, axes of decametric and kilometric folds trend more or less W-E in the Mushenie Formation. This also applies for the part of the Kamanyola Formation located in the core of the Mt. Bangwe anticline.

Directions of the D1 fold axes are more or less E-W although the D1 folds are clearly reworked by the D2 folds and D'2 thrusts.

Mineral associations indicate a first paragenesis with quartz, biotite, muscovite sericite, garnet, and tourmaline linked to the S1 schistosity (greenschist facies). That indicates a moderate metamorphic grade. M2 and M3 paragenesis are associated to the D2 and D3 deformation and also indicate a low grade of metamorphism (greenschist facies).

The Kamanyola and the Kashenie formations exhibit a "flysh facies". The numerous doleritic sills parallel to the bedding corroborate the hypothesised flysch environment. The Mushenie Formation exhibits numerous lenses of conglomerate or breccia associated with ferruginous sandstone suggesting sedimentary deposits in a tectonic instable basin.

Radiometric data

Previous radiometric ages

The only published age determinations concern the Late Miocene (10 to 5 Ma) basalts dated by the K/Ar method [START_REF] Pasteels | Timing of the volcanism of the southern Kivu province: implications for the evolution of the western branch of the East African Rift system[END_REF][START_REF] Pouclet | The Cenozoic volcanism in the Kivu rift: assessment of the tectonic setting, geochemistry and geochronology of the volcanic activity in the south Kivu and Virunga regions[END_REF].

The first attempt to date the metasedimentary siliciclastic rocks from the Nya-Ngezie Group was undertaken by Kampunzu et al. (2003a) using detrital zircon from coarse-grained sandstone samples of the Bangwe Formation at the base of the Nya-Ngezie Group applying the SHRIMP method. The majority of the 207 Pb/ 206 Pb ages plots in a limited range between 1850 and 1950 Ma. Two significantly older zircons with concordant ages at 2290 ± 40 Ma and 2733 ± 11 Ma were also found. The youngest detrital zircon group has a concordant 207 Pb/ 206 Pb age of 1222 ± 28 Ma. However, due to the death of A.B. Kampunzu in 2004, the initial project to publish these results collapsed (Kampunzu et al., 2003a and2003b, unpublished).

New radiometric ages

In 2013, four samples from the Nya-Ngezie Group were studied for their detrital zircon age patterns in order to control the previous data. To compare these results with the underlying Bugarama Group that is supposedly coeval with the Burundian groups of Rwanda and Burundi, two additional samples from the Bugarama Group were also studied for their detrital zircon age patterns. Biotite from another four samples from the Bugarama Group were analysed by the 40 Ar/ 39 Ar method in order to date the Kibaran metamorphism. But, only pan-African or Mio-Pliocene ages were found in 2015 by this approach. Thus, only the age data of detrital zircon of six samples is presented below.

Sampling

Four samples have been selected in the Nya-Ngezie Group: NG1 (N2°41'39.9" / W28°53'51.8") from the Bangwe Formation is a quartzite with ripple-marks collected at the Bushinga pass. NG3 (N2°41'45.2" / W28°51'39.9") from the Mukubio Formation is a banded quartz phyllite rock from the Bangwe Anticline. NG4 (N 2°43'19.5"/ W28°50'06.6") and NG2 (N2°42'43.8"/ W28°50'19.5") are both quartzitic sandstones from the Mughera Formation of the Mughera Syncline.

Two samples have been selected in the Bugarama Group: NG5 (N2°41'86.0" / W28°57'02.0") is a grey micaschist from the lower part of the Kamanyola Formation, sampled along the road from Nya-Ngezie to Bujumbura. NG6 (N2°42'23.0" / W28°58'00.0") is a garnet-bearing quartz micaschist from the Kashenie Group.

Methods

Sample preparation

Due to small sample sizes, not more than ca. 0.3 kg of each fresh sample was crushed in a jaw crusher. After this, the material was sieved for the 36 to 400 µm fraction. Heavy mineral separation from the latter was done using LST (lithium heteropolytungstate in water) prior to magnetic separation in the Frantz isomagnetic separator. Zircon grains for U-Pb dating were selected by hand-picking under a binocular microscope (ZEISS Stemi 2000-C). In order to get a representative selection of the overall zircon population, at least 120 zircon grains of all sizes, colours and morphologic types were randomly picked from each sample if possible [START_REF] Fedo | Detrital Zircon Analysis of the Sedimentary Record[END_REF][START_REF] Link | Reliability and longitudinal change of detritalzircon age spectra in the Snake River system, Idaho and Wyoming: An example of reproducing the bumpy barcode[END_REF]. Nevertheless, some samples contained less than 120 grains.

Subsequently, the zircons were mounted in resin blocks and polished to approximately half their thickness in order to expose their internal structure. Thus, CL-imaging was performed using SEM coupled to a HONOLD CL-detector operating with a spot size of 550 nm at 20 kV.

U-Pb age determination and Th-U measurement via LA-ICP-MS

In order to avoid mixed U-Pb ages resulting from different late-to postmagmatic or metamorphic influences, spots for isotope analyses were preferentially set on monophase growth patterns. U-Th-Pb isotopic analyses took place between 2013 and 2014 at the GeoPlasma Lab, Senckenberg Naturhistorische Sammlungen Dresden and were carried out via LA-ICP-MS (Laser Ablation with Inductively Coupled Plasma Mass Spectrometry) techniques. Therefore, a Thermo-Scientific Element 2 XR instrument coupled to a New Wave UP-193 Excimer Laser System was used (for data see electronic supplement, NG Radiometric tables). The mounts were put into a teardrop-shaped, low volume laser cell, produced by Ben Jähne (Dresden), for ablation. Due to its fast wash-out this cell allows sequential sampling of heterogeneous grains (e.g. growth zones) during time-resolved data acquisition. Single measurement of one spot is composed of approximately 15 s background acquisition followed by 30 s data acquisition. With respect on grain structure and size, the chosen spot sizes ranged between 25 (very few grains) and 35 µm. If necessary, correction of common-lead was carried out, based on the interference-and background-corrected 204 Pb signal and a model Pb composition [START_REF] Stacey | Approximation of terrestrial lead isotope evolution by a twostage model[END_REF]. Judgement of necessity for correction depended on whether the corrected 207 Pb/ 206 Pb lay outside the internal errors of the measured ratios. A U-Pb analysis is concordant when it overlaps within uncertainty with the Concordia. So, it seems to be appropriate to exclude results with a low level of concordance ( 206 Pb/ 238 U age / 207 Pb/ 206 Pb age × 100), but very large errors that overlap with the Concordia from interpretation. Thus, an interpretation with respect to the obtained ages was done for all grains within the concordance interval of 90-110 % ( 206 Pb/ 238 U age / 207 Pb/ 206 Pb age × 100) which is often used (e.g. [START_REF] Spencer | Strategies towards statistically robust interpretation of in situ U-Pb zircon geochronology[END_REF]. Discordant analyses were generally interpreted with caution. Finally, raw data were corrected for background signal, common-Pb, laser induced elemental fractionation, instrumental mass discrimination, depth-and timedependant elemental fractionation of Pb/Th and Pb/U by use of an Excel® spreadsheet program developed by Axel Gerdes (Institute of Geosciences, Johann Wolfgang Goethe-University Frankfurt, Frankfurt am Main, Germany). The given uncertainties were propagated by quadratic addition of the external reproducibility obtained from the standard zircon GJ-1 (~0.6 % and 0.5-1.0 % for the 207 Pb/ 206 Pb and 206 Pb/ 238 U, respectively) during individual analytical sessions and the within-run precision of each analysis. Each sequence started with five measurements of the GJ-1 zircon, followed by ten analyses of unknown grains, three spots on GJ-1 and so on. The obtained calculated Concordia ages for the GJ-1 reference zircon varied between 606.5 ± 2.6 and 606.8 ± 2.8 Ma (ntotal = 428) for each analytical session (14 < n < 38 analyses per session), which is in line with the published ages (e.g. [START_REF] Jackson | The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U-Pb zircon geochronology[END_REF][START_REF] Horstwood | Community-Derived Standards for LA-ICP-MS (U-Th-Pb) Geochronology -Uncertainty Propagation, Age Interpretation and Data Reporting[END_REF]and references therein). Concordia diagrams (2σ error ellipses) and concordia ages (95 % confidence level) were produced by using Isoplot/Ex 4.13 [START_REF] Ludwig | User manual for Isoplot/Ex rev. 2.49[END_REF]. The program Age Display [START_REF] Sircombe | AGEDISPLAY: an EXCEL workbook to evaluate and display univariate geochronological data using binned frequency histograms and probability density distributions[END_REF] was employed to generate frequency as well as relative probability plots. For zircons with ages older than 1 Ga, 207 Pb/ 206 Pb ages were taken for interpretation, the 206 Pb/ 238 U ages for younger grains. Further details on analytical protocol and data processing are reported in Gerdes andZeh (2006, 2009).

The general method for the age determination of rutile resembles that for zircon. A major aspect is the age discrepancy of the reference rutile as secondary standard when measured against a reference zircon as primary standard, which is likely caused by matrix effects [START_REF] Luvizotto | Rutile crystals as potential trace element and isotope mineral standards for microanalysis[END_REF]. Therefore, the ages and corresponding ratios of the unknown analyses have to be recalculated according to the deviation of the measured reference rutile ages from that given in the literature. In general, the use of a reference rutile as primary standard would be preferable, but as only the poorly defined SQR36 standard was available [START_REF] Schmitt | High-sensitivity U-Pb rutile dating by secondary ion mass spectrometry (SIMS) with an O2+ primary beam[END_REF], it seemed to be a better choice to use the very well defined reference zircon GJ-1 as primary standard [START_REF] Jackson | The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U-Pb zircon geochronology[END_REF]. Ages received from the reference rutile measured against the GJ-1 standard had to be corrected, for the obtained offset in age (1957± 7 Ma, n = 16, vs. 1998± 6 Ma and 2001 ± 7 Ma, [START_REF] Schmitt | High-sensitivity U-Pb rutile dating by secondary ion mass spectrometry (SIMS) with an O2+ primary beam[END_REF].

Results

A total of 736 zircon grains was analysed for their U-Pb ages and 391 of them gave ages within an interval of concordance between 90 and 110% ("concordant" ages). If not explicitly mentioned, all following ages refer to zircon grains within this interval.

Age determinations from the Bugarama Group were done on samples NG5 and NG6. Sample NG6 yielded only two grains (of six dated) with ages at 1765 ± 24 Ma and 1889 ± 35 Ma. The paucity of concordant ages in NG6 and their occurrence in all samples (Fig. 4) limits the informative value of this sample with respect to provenance analysis. Unfortunately, the analysis of detrital rutile did not give any interpretable results. Forty five of 112 measured grains of sample NG5 yielded ages in a large span ranging from the Archaean (2820 ± 20 Ma) to the end of the Mesoproterozoic (1181 ± 69 Ma). Orosirian and Statherian ages occur frequently together with abundant Calymmian and Ectasian zircon ages. The youngest grain in NG5 shows an apparent age at 1181 ± 69 Ma, while the second youngest grain was dated at 1207 ± 28 Ma. Due to the large error of the youngest grain, which completely overlaps with the error of the second, the age at 1207 ± 28 Ma should be considered as the maximum age of deposition of the Bugarama Group. Anyway, the deposition is assumed to have happened in the post-1250 Ma Late Ectasian.

Age determinations from the Nya-Ngezie Group were done on samples NG1 (90/208 grains 90-110% conc.), NG2 (95/143 grains 90-110% conc.), NG3 (106/142 grains 90-110% conc.) and NG4 (53/114 grains 90-110% conc.). Detrital zircon age distribution patterns in NG1 of the Bangwe Formation and NG3 of the Mukubio Formation are very similar (Fig. 4). Both samples show an age peak around 1900 to 1800 Ma, while few zircon grains form a cluster with Kibaran ages between 1400 and 1200 Ma. However, NG1 exhibits some Archaean zircon ages comparable to those of NG5. Comparable ages were not found in NG3. NG2 and NG4 of the Mughera Formation have strong similarities with several age peaks between 1400 and 1100 Ma and zircon ages between 2200 and 1600 Ma. One grain of NG4 yielded an age around 2670 Ma that has no counterpart in NG2. The obtained detrital zircon age distribution patterns suggest a similar origin for sediments of the Bangwe (NG1) and Mukubio (NG3) formations. The age distribution patterns for the samples of the Mughera Formation (NG2, NG4) suggest a different origin. In any case, sedimentological investigations point to a source very proximal to the Nya-Ngezie area for the latter samples. Another major result concerns the maximum deposition ages of the Nya-Ngezie Group sediments Group, which are 1250 ± 18 Ma for NG1 (four youngest grains), 1216 ± 14 Ma for NG3 (five youngest grains), 1160 ± 19 Ma for NG4 (four youngest grains), and 1121 ± 14 Ma for NG2 (two youngest grains). These ages are consistent with the youngest ages (1222 ± 28 Ma) reported by Kampunzu et al. (2003a) in zircon grains from a sample located stratigraphically below NG1. Thus, the Nya-Ngezie Group is not older than 1250 Ma, and likely even as young as ca. 1120 Ma. The assumed age of the final deposition has to be set around 1000 Ma, which is the age of the first post-tectonic granites [START_REF] Cahen | Rubidium-Strontium geochronology of some granitic rocks from the Kibaran belt (central Katanga, Republique of Congo)[END_REF][START_REF] Cahen | The Geochronology and Evolution of Africa[END_REF].

A detailed list of all obtained radiometric results can be found in the supplementary tables, which are available from the journal website.

Discussion

Owing to the new results presented above, there are two main questions: 1) When was the likely time of deposition of the sediments and what is the age of the tectonic climax? 2) What is the potential origin of inherited zircons and location of potential source rocks?

Time of deposition of the Bugarama Group

The youngest detrital zircon grains at 1207 ± 28 Ma suggest a Stenian (Late Mesoproterozoic) age for the deposition of the Bugarama Group that was initially ascribed to the Ruzizian (Palaeoproterozoic) basement [START_REF] Boutakoff | Géologie des territoires situés à l'Ouest et au Nord-Ouest du fossé tectonique du Kivu[END_REF][START_REF] Safianikoff | Les systèmes de l'Urundi et de la Ruzizi au Kivu et les intrusions granitiques[END_REF] or to the Burundian (Early to Middle Mesoproterozoic) by [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF] and Cahen et al. (1979). Previously, no metamorphic rocks younger than 1.25 Ga or 1.20 Ga have been reported in the KVB area except for the metamorphic rings linked to the tin bearing granites, which intruded during the Early Neoproterozoic (1000 Ma to 960 Ma, [START_REF] Cahen | Rubidium-Strontium geochronology of some granitic rocks from the Kibaran belt (central Katanga, Republique of Congo)[END_REF][START_REF] Cahen | The Geochronology and Evolution of Africa[END_REF]. With respect to the S1 folding and the metamorphism of the Bugarama Group prior to the deposition of the Nya-Ngezie Group, an older age has been expected. The 1121 ± 14 Ma of the youngest inherited zircon in the overlying Nya-Ngezie Group could be the age of the Bugarama metamorphism, which could be coeval to the D1 deformation.

Time of deposition on the Nya-Ngezie Group

The duration of deposition of the Nya-Ngezie Group remains unknown. However, it should be younger than the time bracket between 1121 ± 14 Ma (youngest inherited zircons) and the 1111 ± 38 Ma (Lavreau and Liégeois, 1982) which is the presumed age of the D2 tectonic event in Rwanda. In any case the D2 and D'2 tectonic events reported in the Nya-Ngezie Group are younger than 1121 ± 14 Ma and older than the ca. 710 Ma age, which is recorded in zircons from samples collected in the Nya-Kasiba basal conglomerates (Kampunzu et al., 2003b, unpublished). Many authors, among them [START_REF] Caron | Les ressources minérales d'âge protérozoïque moyen en Afrique équatoriale et l'évolution géodynamique de la chaine Kibarienne[END_REF], assume that D2 is younger than the widespread 960-1000 Ma tin bearing granites.

Possible source rocks

Despite they belong to two different groups there are some similarities between the detrital zircon age distribution patterns in samples NG6, NG1, and NG3 on one hand and NG5, NG4 and NG2 on the other. This could be caused by temporally changing delivery of siliciclastic detritus of potential source rocks.

The main question concerns the origin of the Archaean zircon grains identified in samples NG1, NG4, and NG5 and also by Kampunzu et al. (2003a) at the base of the Nya-Ngezie Group, because no Archaean outcrop has yet been described in the vicinity of the Nya-Ngezie area. A hidden Archaean massif is presumed elsewhere around, but a provenance from the Tanzanian Craton cannot be excluded. Furthermore, a provenance as recycled grains from the Palaeoproterozoic basement is also possible.

The Ruzizian basement with published ages between 2100 and 1700 Ma [START_REF] Brick | Palaeoproterozoic eclogite formation in Tanzania: a structural, geochronological, thermochronological and metamorphic study of the Usagaran and Ubende orogenic belts[END_REF] is thought to have provided zircons in all six samples. Sedimentary investigations (Fig. 3) indicate either a northern or a southern origin for the siliciclastic rocks. To the south, [START_REF] Cahen | The geochronology of Equatorial Africa[END_REF] obtained a Ruzizian Rb/Sr age at 1960 ± 170 Ma for the "Mojangjo" granite, cropping out in the north of Uvira (northern Tanganyika Lake). To the north, the nearest basement inlier with a Ruzizian age has been found at Runyinya (close to Butare) some 60 km away from the working area (Gerards and Ledent, 1970).

Mesoproterozoic zircon grains with ages between 1500 and 1200 Ma are present in every sample except NG6, which is likely due to the paucity of zircon in this sample. They can likely be provided by the Burundian granitoids dated in Rwanda and Burundi. The closest dated granitic massifs crop out in northwestern Burundi [START_REF] Brinckmann | La géologie et la minéralisation primaire de l'Or de la chaine Kibarienne, Nord-Ouest du Burundi, Afrique orientale[END_REF]. Furthermore, the Kigarama / Akanyaru granite provided an Rb/Sr age of 1265 ± 45 Ma, and the Cibitoke / Kaburantwa granite yielded a U-Pb zircon age of 1210 ± 2 Ma. Both are considered as post tectonic by [START_REF] Brinckmann | La géologie et la minéralisation primaire de l'Or de la chaine Kibarienne, Nord-Ouest du Burundi, Afrique orientale[END_REF].

Conclusions from the new age determinations

Amongst the three main groups evidenced forty years ago [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF], the two lower have been correlated either to the Upper or Lower Burundian or also to the Ruzizian basement. Such discrepancies should be assigned to the lack of absolute age determinations. Now, it is known that the Nya-Ngezie and Bugarama groups belong to a late Kibaran-Burundian orogenic stage. Only the granitic basement cropping out in the lower Ruzizi valley is not yet dated but its linkage to the Bugarama Group metamorphism is strongly suspected [START_REF] Brinckmann | La géologie et la minéralisation primaire de l'Or de la chaine Kibarienne, Nord-Ouest du Burundi, Afrique orientale[END_REF]. This local study also confirms that a late metamorphic stage around 1120 Ma likely exists in the Kibaran-Burundian Orogen. The six new detrital zircon age spectra in the Nya-Ngezie and Bugarama groups provide useful information on the position of these two groups with respect to the western and eastern neighbouring terranes. Up to now, the stratigraphic position of these groups remained unclear with respect to the main western Burundian unit (Luemba-Bitale Supergroup), but the new data favours the hypothesis of a post-Luemba-Bitale deposition. These new age determinations also revealed a late molassic stage at the end of the Mesoproterozoic. This is interpreted as witness of late orogenic uplift and subsequent erosional processes. Contrary to [START_REF] Pöhl | Metallogeny of the northeastern Kibara belt, central Africa-recent perspectives[END_REF], our results show that the Kibaran sedimentary deposition was not terminated at around 1.20 Ga. Thus, three groups of Kibaran belts can be distinguished: the early and middle groups that are separated by the Luemba unconformity and the late group, which is cropping out in the Nya-Ngezie area and predates the opening of the pan-African Itombwe trough.

Correlations and consequences on the Kibaran-Burundian belts

Obviously, the new radiometric results have some consequences on the evolution of different parts of the Kibaran-Burundian belts. This applies particularly for the KVB, but also affects the adjacent KAB, KIB, and Irumide (IRB) belts under the assumption that the published stratigraphic correlations are more or less correct.

Consequences on the Kivu Belt (KVB)

The last attempt to correlate the formations of the eastern Kivu area, [START_REF] Villeneuve | Apports de l'imagerie spatiale à la résolution des structures géologiques en zone équatoriale: exemples du Précambrien au Kivu (Congo Oriental)[END_REF] suggested four different Burundian units separated by three major unconformities. Out of the two lower units, ascribed to the Palaeoproterozoic and to the Lower Burundian (> 1380 Ma), they distinguished an Upper Burundian unit including the large majority of the Kivu trenches evidenced by [START_REF] Villeneuve | Les sillons plissés du Brundien supérieur dans la chaine Kibarienne d'Afrique centrale[END_REF] and the two groups of the Nya-Ngezie area. They considered two hypotheses depending on whether the Nya-Ngezie Group is older or younger than other formations of the Kivu area, classified as Upper Burundian.

Furthermore, the Bugarama Group was correlated to the Lower unit of Lower Burundian age with respect to its metamorphism. However, the lack of radiometric data prevented any robust correlation. Now, taking into account the newly obtained radiometric data, we propose a revised correlation throughout the KVB. These correlations are based on the lithostratigraphic characteristics (four lithostratigraphic units), on the tectonic events (nine tectonic events), on the granitic magmatic events (four events), and on the metamorphic events (five events) that are explicitly explained in a separate paper devoted to the Kivu Belt, (Villeneuve et al., in progress).

The lithostratigraphic column presented in table I considers the correlations between the western and eastern Kivu units that are proposed elsewhere (Villeneuve et al., in progress). Apart from the two main units Kv1 and Kv2, considered by [START_REF] Villeneuve | Les sillons plissés du Brundien supérieur dans la chaine Kibarienne d'Afrique centrale[END_REF], two new units (Kv3 and Kv4) are delineated corresponding to the newly dated Bugarama and Nya-Ngezie groups, respectively. The metamorphic Bugarama Group is linked to the Bikangala Group [START_REF] Rumvegeri | Le Précambrien de l'Ouest du lac Kivu (Zaire) et sa place dans l'évolution Géodynamique de l'Afrique centrale et orientale[END_REF], to the Masisi Group of the northern Kivu Lake, and likely to the "Burundien superieur" of Burundi as well as the Rugezi Group of the Burundian of Rwanda. In contrast, an equivalent to the metasedimentary Nya-Ngezie Group is only evidenced in the "serie supérieure" of the Kirotshe area [START_REF] Blès | Etude photo-interprétative et reconnaissance géologique et structurale de la zone exclusive de recherches Masisi-Saké[END_REF]. The lithological details of these four units and further parameters for the correlations are discussed in Villeneuve et al. (in progress).

Owing to the lack of robust radiometric studies, the relationships between the granitic bodies and the sedimentary deposits have not been debated here. The few granitic bodies dated by the Rb/Sr method (Nzombe, Kasika, Nyamakubi, Numbi, Kirumba, Kalehe, etc.) display a panel of pan-African ages, which are not in agreement with field observations [START_REF] Pasteels | Géologie et pétrographie de la région de Kirotshe (Kivu)[END_REF]Blés, 1972;[START_REF] Burg | Contraintes petro-structurales dans l'évolution de la chaine Kibarienne au Kivu (Zaire)[END_REF][START_REF] Villeneuve | Géologie du synclinal de l'Itombwe (Zaïre Oriental) et le problème de l'existence d'un sillon plissé pan-africain[END_REF]. According to [START_REF] Blès | Etude photo-interprétative et reconnaissance géologique et structurale de la zone exclusive de recherches Masisi-Saké[END_REF], [START_REF] Burg | Contraintes petro-structurales dans l'évolution de la chaine Kibarienne au Kivu (Zaire)[END_REF], and [START_REF] Kampunzu | Les Kibarides d'Afrique centrale et orientale: une chaine de collision[END_REF] the Kasika and Mt. Hango granitoids are considered as post-Burundian despite they appear to be synkinematic with the Burundian host rocks. The best example of discrepancy between radiometric dating and field observations is the Kasika granite which looks like concordant with the Kv2 metasedimentary host rocks [START_REF] Burg | Contraintes petro-structurales dans l'évolution de la chaine Kibarienne au Kivu (Zaire)[END_REF]) but has been dated at about 986 ± 10 Ma by U-Pb on zircon [START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF]. Another source of confusion is caused by similarities between the metamorphic events registered in the Bugarama Group (Kv3) and in the Kv2 unit rocks, since both metamorphic events resulted in quite similar lithologies and mineral compositions (sillimanite, kyanite, staurolite, garnet and biotite). All these granitic and metamorphic events are described in detail in the paper devoted to the KVB (Villeneuve et al., in progress), but clearly, this area needs some more age determinations to be correctly correlated to the adjacent regions.

Consequences on the Karagwe Ankolean Belt (KAB)

The KAB includes Rwanda, Burundi, as well as parts of Uganda and Tanzania [START_REF] Koegelenberg | Tectonic wedging, back-thrusting and basin development in the frontal parts of the Mesoproterozoic Karagwe Ankole belt in NW Tanzania[END_REF]. The first synthetic paper devoted to the geology of Rwanda was published by Gerards and Ledent (1970), whereas the first synthetic map was coordinated by [START_REF] Ziserman | Données sur la métallogenie du Rwanda. Enseignements tirés de la carte des gites mineraux[END_REF]. Similar investigations have been performed in Burundi with the assistance of the Royal African Museum of Tervuren [START_REF] Klerkx | Granitoides Kibariens précoces et tectonique tengentielle au Burundi: magmatisme bimodal lié à la distension crustale[END_REF][START_REF] Radulescu | Carte géologique et esquisse metallogénique du Burundi[END_REF][START_REF] Theunissen | Carte géologique du Rwanda 1:200.000. Service géologique[END_REF][START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF][START_REF] Fernandez-Alonso | The Mesoproterozic Karagwe-Ankole belt (formerly the NE Kibara belt): The result of prolonged extensional intracratonic basin development punctuated by two short-lived farfield compressional events[END_REF]. Between 1998 and 2001, the BGR (Hannover, Germany) conducted some geological and metallogenic studies in the northwestern part of Burundi adjacent to the Nya-Ngezie area [START_REF] Brinckmann | La géologie et la minéralisation primaire de l'Or de la chaine Kibarienne, Nord-Ouest du Burundi, Afrique orientale[END_REF]. Similar investigations have been performed in northern Rwanda by Pohl (1992Pohl ( , 1994)). According to [START_REF] Tack | Kibaran A-type granitoids and mafic rocks generated by to mantle sources in a late orogenic setting (Burundi)[END_REF], the KAB can be split in two parts: the eastern domain (ED or EED) and the western domain (WD or WID). Both are separated by a magmatic zone from each other [START_REF] Tack | Kibaran A-type granitoids and mafic rocks generated by to mantle sources in a late orogenic setting (Burundi)[END_REF][START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF][START_REF] Fernandez-Alonso | The Mesoproterozic Karagwe-Ankole belt (formerly the NE Kibara belt): The result of prolonged extensional intracratonic basin development punctuated by two short-lived farfield compressional events[END_REF] called TZ by [START_REF] Tahon | New insights about the evolution of the Mesoproterozoic Northeastern Kibarabn belt (Central Africa)[END_REF]. The lithostratigraphic successions in the WD refer to the stratigraphic scale established by [START_REF] Baudet | Lithostratigraphie du domaine sédimentaire de la chaine Kibarienne au Rwanda[END_REF], which considers four groups: the Gikoro and Pindura groups at the base and the Cyohoha and Rugesi groups on top. Table I presents our attempt to correlate the Kivu Belt (KVB) to the WD and the ED. This table considers the five units (Kv1 to Kv4 plus K5) described in the Kivu Belt and their supposed counterpart (Ka1 to Ka5) in the Karagwe Ankole Belt. In conclusion of a meeting held in Tervuren in 1976 [START_REF] Cahen | Réunion de travail des 1, 2 et 3 septembre 1975: La géologie des terrains précambriens voisins du fossé tectonique occidental, spécialement dans les régions sises de part et d'autre de la partie sud du lac Kivu et du nord du lac Tanganyika, au Kivu, au Rwanda et au Burundi[END_REF], we admitted an equivalence of the Bugarama Group with the formations of Bugarama-Karengera evidenced in Rwanda [START_REF] Frautschi | Feuille Cyangugu. Rapp. Année[END_REF], and with those cropping out in the Mabayi-Cibitoke area in Burundi. However, [START_REF] Radulescu | Carte géologique et esquisse metallogénique du Burundi[END_REF] ascribed them to the Ruzizian basement in the geological map of Cibitoke. Later on, [START_REF] Theunissen | Carte géologique du Burundi, Feuille Cibitoke, S3-20SW, République du Burundi[END_REF] classified these formations -called the Buganda-Ruhanda Complex -as the lower part of the Middle Burundian Group and ascribed the interbedded volcano-sedimentary Butahana-Murwi-Ngozoi and Mwokora formations to the upper part of the Middle Burundian Group. Subsequent geological investigations by [START_REF] Brinckmann | La géologie et la minéralisation primaire de l'Or de la chaine Kibarienne, Nord-Ouest du Burundi, Afrique orientale[END_REF] present a different interpretation. These authors assume an Upper Burundian relation for those terranes cropping out in areas in Burundi that are close to the Kamanyola and Kashenie localities. Two radiometric age determinations on the post tectonic granitoid of Cibitoke-Kabaruntwa (1210 ± 3 Ma and 1212 ± 2 Ma) were published by [START_REF] Brinckmann | La géologie et la minéralisation primaire de l'Or de la chaine Kibarienne, Nord-Ouest du Burundi, Afrique orientale[END_REF]. This prevents us to correlate the Bugarama or the Nya-Ngezie Group with these adjacent Mesoproterozoic formations of Burundi, taking into account that zircon grains from these granites are included in the Bugarama sediments. A correlation with the Kv2 formations of Luemba, Bitale and Luntukulu fits better. Moreover, the Bugarama-Karengera Formation of Rwanda is thrust over the Bugarama Group. This thrust is exposed on the northern side of the Ruzizi River.

A correlation with the WD of Rwanda and Burundi by [START_REF] Fernandez-Alonso | The Mesoproterozic Karagwe-Ankole belt (formerly the NE Kibara belt): The result of prolonged extensional intracratonic basin development punctuated by two short-lived farfield compressional events[END_REF] linked the Bugarama Group to the Gikoro and Pindura groups. Likewise, the authors correlated the post 1375 Ma sedimentary deposits with the whole Nya-Ngezie Group. In our opinion these correlations should concern the Kv2 formations (including the Cyohoha and Rugesi groups) rather than the Nya-Ngezie Group (Kv4). This is more consistent with the 1300-1190 Ma detrital zircon ages found in samples NG2 and NG4. The last part of the KAB crops out in southern Uganda where the Karagwe-Ankolean units that cover the Palaeoproterozoic Kibalian / Ruwenzorian terranes [START_REF] Westerhof | Geology and geodynamic Development of Uganda with explanation of th 1.1 000.000 Scale Geological map[END_REF]. These metasedimentary and metamorphic formations are accompanied by large plots of "arena granites" [START_REF] Wayland | Geology of Uganda[END_REF] which have been dated in 1972 by the Rb/Sr isochron method and displayed ages between 1278 ± 58 Ma and1146 ± 40 Ma (Vernon-Chamberlain and[START_REF] Vernon-Chamberlain | Age and isotope studies on the "arena" granites of SW Uganda[END_REF]. However, new U-Pb age determinations on zircon from the same "arenas" massifs (Buchwald et al., 2008) show three age groups: one at around 1566 Ma, the second at about 1444 Ma and the third clusters between ca. 1368 and 1329 Ma. Thus, the Rb/Sr data is likely linked to later tectono-magmatic events rather than the emplacement of granitic intrusions.

Finally, lithostratigraphic correlations between the KVB and the KAB are exposed in table I. Surprisingly, no reliable counterpart of the Nya-Ngezie Group has been formally evidenced in the KAB throughout the geological literature, although the Upper Burundian Rugendo-Mabayi-Sagahanga Formation [START_REF] Theunissen | Carte géologique du Burundi, Feuille Cibitoke, S3-20SW, République du Burundi[END_REF]) exhibits some similarities with the Nya-Ngezie Group. Furthermore, the "Miyove" Formation is not older than 1250 Ma, and likely even as young as ca.

1120 Ma. This formation, which lies on top of the Rugesi Group, has been considered as a possible counterpart of the Nya-Ngezie Group. However, this Miyove Formation was involved in the Cyohoha and Rugesi tectonic events, and therefore should be associated to the Ka2.

In addition, two schematic cross sections have been drawn across the northern and southern parts of the KVB and KAB (Fig. 5). They highlight the opposite vergence on both sides of the Kibaran Belt, on the Congo Craton to the west and on the Tanzanian Craton to the east.

These cross sections show that the Kv1 and Ka1 units are capped by the Kv2 and Ka2 trenches. It has to be noted that the Kv4 unit does not crop out along these cross-sections.

Consequences on the Kibaride Belt (KIB)

The Kibara Mountains in the northern part of the Katanga province (Shaba) are among the first [START_REF] Magnée (de) | Coupe géologique dans les monts Kibara[END_REF][START_REF] Robert | Notice de la carte géologique du Katanga à l'échelle du 1.000.000. Note preliminaire[END_REF][START_REF] Robert | Contribution à la géologie du Katanga. Le systeme des Kibaras et le complexe de base[END_REF][START_REF] Robert | Géologie du Katanga. Les formations du soubassement ancien[END_REF][START_REF] Mortelmans | Stratigraphie et tectonique des mont Kibara dans la région Mitwaba-Kina[END_REF][START_REF] Van De Steen | Le système des Kibaras[END_REF] and the best studied areas of the Kibaran Orogen. It is also one of the first absolutely dated areas by geochronological methods [START_REF] Cahen | The geochronology of Equatorial Africa[END_REF][START_REF] Cahen | Rubidium-Strontium geochronology of some granitic rocks from the Kibaran belt (central Katanga, Republique of Congo)[END_REF][START_REF] Cahen | A comparison of the ages of granites of S.W. Uganda with those of the Kibaran of Central Shaba (Katanga), Rep. Zaire with some new isotopic and petrogenetical data[END_REF][START_REF] Cahen | The Geochronology and Evolution of Africa[END_REF]. The last studies conducted by [START_REF] Kokonyangi | Geological evolution of the Kibarides belt, Mitwaba, Democratic Republic of Congo, Central Africa[END_REF][START_REF] Kokonyangi | U-Pb zircon geochronology and petrology of granitoids from Mitwaba (Katanga, Congo): implications for the evolution of the Mesoproterozoic Kibaran belt[END_REF]Kokonyangi et al. ( , 2005Kokonyangi et al. ( , 2006[START_REF] Kokonyangi | U-Pb SHRIMP dating of detrital zircons from the Nzilo group (Kibaran belt): implications for the source of sediments and Mesoproterozoic evolution of central Africa[END_REF] from the Lubumbashi University under the supervision of A.B. Kampunzu were completed by [START_REF] Debruyne | Regional geodynamic context for the Mesoproterozoic Kibara belt (KIB) and the Karagwe-Ankole belt: Evidence from geochemistry and Isotopes in the KIB[END_REF]. The Kibaran basement was dated in several places at around 2 Ga by Delhal and Liégeois (1982). The basement is capped by sandstones and volcanic tuffs especially in the Marungu area. The beginning of sedimentary deposition is ascribed to the Kibaran Orogeny and seems to have happened at around 1.4 Ga. In accordance to publications of the last two decades (Kokonyangi, 2006[START_REF] Kokonyangi | U-Pb SHRIMP dating of detrital zircons from the Nzilo group (Kibaran belt): implications for the source of sediments and Mesoproterozoic evolution of central Africa[END_REF][START_REF] Debruyne | Regional geodynamic context for the Mesoproterozoic Kibara belt (KIB) and the Karagwe-Ankole belt: Evidence from geochemistry and Isotopes in the KIB[END_REF], the Kibara succession includes four main groups. They are from the base to the top: the Kiaora, Nzilo, Hakanson, and Lubudi groups. The Kiaora Group shows a strong cleavage (S1), which was acquired prior to the deposition of the Nzilo Group [START_REF] Byamungu | A propos du Kibarien (Precambrien moyen) de la région du barrage de Nzilo (Shaba, Zaire)[END_REF] and is linked to NE-SW structures to the south and E-W structures to the north. Magmatic rocks associated to the Kiaora Group display ages between 1.40 and 1.38 Ga (Kokonyangi et al., 2006). Such zircon ages have been recorded in sediments of the covering Nzilo Group and in the post-Kiaora Kataba conglomerate (1329 ± 32 Ma) according to [START_REF] Cahen | The Geochronology and Evolution of Africa[END_REF] and [START_REF] Kokonyangi | U-Pb SHRIMP dating of detrital zircons from the Nzilo group (Kibaran belt): implications for the source of sediments and Mesoproterozoic evolution of central Africa[END_REF]. According to [START_REF] Kampunzu | Les Kibarides d'Afrique centrale et orientale: une chaine de collision[END_REF] and Kokonyangi et al. (2006) the Kiaora Group underwent a second tectonic folding (associated to a S2 cleavage) with a NNE-SSW trend, which marks the only witness of a tectonic event registered in the three other groups. This second tectonic event is associated to a second magmatic event that likely occurred at around 1306 ± 35 Ma. Finally, according to [START_REF] Debruyne | Regional geodynamic context for the Mesoproterozoic Kibara belt (KIB) and the Karagwe-Ankole belt: Evidence from geochemistry and Isotopes in the KIB[END_REF], a third magmatic event took place at around 1070 Ma (1079 ± 14 Ma and 1050 ± 50 Ma) prior to the intrusion of the post-Kibaran tin granites (1000 to 960 Ma) according to [START_REF] Cahen | Rubidium-Strontium geochronology of some granitic rocks from the Kibaran belt (central Katanga, Republique of Congo)[END_REF][START_REF] Cahen | The Geochronology and Evolution of Africa[END_REF] and [START_REF] Kokonyangi | U-Pb SHRIMP dating of detrital zircons from the Nzilo group (Kibaran belt): implications for the source of sediments and Mesoproterozoic evolution of central Africa[END_REF].

According to the available radiometric data, the lithostratigraphic subdivisions for the KVB and KAB used in table I have been applied to the KIB. This underlines the lack of sedimentary deposition between 1250 or 1180 Ma and the first Katangian (Neoproterozoic) deposits. Nevertheless, numerous magmatic events were found and dated at around 1080 Ma [START_REF] Debruyne | Regional geodynamic context for the Mesoproterozoic Kibara belt (KIB) and the Karagwe-Ankole belt: Evidence from geochemistry and Isotopes in the KIB[END_REF]. In table I only two units have been distinguished (Ki1 and Ki2) for the KIB and correlated to the lithostratigraphic units of the KVB and KAB. Thus, the Ki1 unit is correlated to the Kv1 and Ka1 units, while the Ki2 is thought to be linked to the Kv2 and Ka2.

Sediments corresponding to the Bugarama (Kv3) and Nya-Ngezie (Kv4) groups are also lacking in the KIB.

In table I a large part of dated granitic intrusions have been reported. The age range of these granitic occurrences indicates that periods without granitic events are rather rare.

Consequences on the Ubendian Belt

Between the northern KVB / KAB and the southern KIB, there is an enigmatic NW-SE elongated structure setting on both sides of the Tanganyika Lake that straddles the DR Congo and Tanzania. In past times this structure was ascribed to the Ruzizian and now to the Ubendian Palaeoproterozoic belt (Dewaele et al., 2003(Dewaele et al., , 2006)). On the Congolese side, this NW-SE structure cuts the NS trending "Luiko syncline" considered as the southern part of the "Luemba syncline" now ranked in the Kv2 unit [START_REF] Villeneuve | Apports de l'imagerie spatiale à la résolution des structures géologiques en zone équatoriale: exemples du Précambrien au Kivu (Congo Oriental)[END_REF]) and shows a NW-SE sinistral strike-slip. On the Tanzanian side, a similar strike-slip movement is evidenced along the "Ufipa shear zone" (Theunissen, 1988a(Theunissen, , 1988b)). The age range of these granitic occurrences indicates that periods without granitic events are rather rare.

Apart from the Ubendian basement, which was well dated by [START_REF] Boven | Timing of exhumation of a high-pressure mafic granulite terrane of the Paleoproterozoic Ubende belt (West Tanzania)[END_REF], several other formations have been described. Among them the "Itiaso metasedimentary group", close to Mgambo, is intruded by the Kapalagulu Igneous Complex dated at 1392 ± 26 Ma [START_REF] Boniface | Mesoproterozoic high-grade metamorphism in pelitic rocks of the northwestern Ubendian belt: implications for the extension of the Kibaran intra-continental basins to Tanzania[END_REF]. To the southeast, the "Wakole terrane" exhibits detrital zircons dated at about 1.4 Ga and was subsequently metamorphosed at 1166 ± 14 Ma and 1007 ± 6 Ma [START_REF] Boniface | Mesoproterozoic high-grade metamorphism in pelitic rocks of the northwestern Ubendian belt: implications for the extension of the Kibaran intra-continental basins to Tanzania[END_REF].

Table I presents our correlations with the adjacent belts. The "Itiaso Group" is clearly an equivalent of the Kv1, Ka1 or Ki1 (= KI), but the southern Wakole terrane could be related to the Ka1, Ka2 or younger strata. The metasediments of the "Luiko syncline" are linked to the Kv2 unit. Until now, no counterpart of the Bugarama or Nya-Ngezie groups, have been found there, although main tectonic features can be related to the D1 and D2 events of the Nya-Ngezie area.

This SE-NW lineament is one of the major tectonic features of this central African domain. It was active at various times from the formation of the Ubendian Belt (Palaeoproterozoic) to the ongoing Cenozoic East African rift system (Mac Connel, 1979;[START_REF] Chorowicz | The East African rift: early stage of a future oceanic opening?[END_REF]Villeneuve, 1983b;[START_REF] Theunissen | Mechanism of inheritance of rift faulting in the western branch of the East African Rift (Tanzania)[END_REF]. Late Kibaran (Theunissen, 1988a) and pan-African [START_REF] Theunissen | Empreinte panafricaine majeure dans la chaine Ubendienne de Tanzanie sud-occidentale; géochronologie U-Pb Zircon et contexte structural[END_REF] reworking have also been detected.

Discussion and synthetic framework (summarised in Table II)

Correlations between the different belts belonging to the "Kibaran System" allow us to propose some synthetic schemes of the whole Kibaran-Burundian Orogen. These synthetic proposals concern the lithostratigrahic scale, the tectonic and metamorphic events, the tectonosedimentary cycles and the geodynamical models. The metamorphic events will be developed apart in another paper.

Unified lithostratigraphic scale

Although there are some stratigraphical differences between the main belts, the numerous similarities cannot be overlooked. Table I points out five lithostratigraphic units: KI to K5.

The K1 unit (with Kv1, Ka1 and Ki1) is represented in the three main belts (KVB, KAB, and KIB). Many authors agree with a stage of deposition that started around 1450 Ma and terminated with the main magmatic event dated at around 1375 Ma [START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF]. Other authors prefer an extensive regime coeval with the 1360 ± 27 Ma magmatic events [START_REF] Klerkx | Granitoides Kibariens précoces et tectonique tengentielle au Burundi: magmatisme bimodal lié à la distension crustale[END_REF]. There are some geological events between the end of the Ruzizian or Ubendian periods and the beginning of the Kibaran-Burundian stage like in the ED. Nevertheless, it would be better to begin the Kibaran Orogen by the opening of basins at about 1.4 Ga. [START_REF] Villeneuve | Les sillons plissés du Brundien supérieur dans la chaine Kibarienne d'Afrique centrale[END_REF] separated this lower unit from the overlying trenches. This hypothesis was then supported by radiometric dating [START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF][START_REF] Fernandez-Alonso | The Mesoproterozic Karagwe-Ankole belt (formerly the NE Kibara belt): The result of prolonged extensional intracratonic basin development punctuated by two short-lived farfield compressional events[END_REF].

The K2 unit (Kv2, Ka2, and Ki2) is present in the KIB, KVB, and the KAB. Possibly, sediments of the "Luiko syncline" and the "Wakole terranes" cropping out in the Ubendian Belt (UBB) belong to this K2 unit. This unit is well studied in the KIB, although the main trenches of the KVB and KAB are linked to this unit. In the KVB and KAB, the lithostratigraphic succession of unit K2 is made of a coarse-grained siliciclastic formation interbedded between two pelitic or shaly formations that led to the trilogy of the Lower, Middle and Upper Urundian. Locally, this succession is capped by a molasse-like formation, e.g. the Miyove Formation of Rwanda, which sometimes was correlated with the above mentioned Nya-Ngezie Group.

The K3 unit (Kv3) is only known in the KVB and dated by our new radiometric results. A possible linkage of the Rugesi Group (KAB) to the K3 unit is not yet proven. Seemingly, the formations of the K2 unit may be confused with those of the K3 unit in many places due to similar petrographic characteristics. The deposition of the K3 unit began after ca. 1207 Ma and terminated prior the deposition of the approximately 1121 ± 14 Ma old overlying Nya-Ngezie Group. Sedimentary deposition was not yet recognised in this time bracket outside the KVB.

The K4 unit (Kv4) is mainly represented by the Nya-Ngezie Group of the KVB. The youngest zircon extracted from the Nya-Ngezie Group displays an age at 1121 ± 14 Ma, while the latest deposits should be older than the post-tectonic granites dated between ca. 976 and 912 ± 30 Ma, with mean ages around 960 Ma. There is only one isolated outcrop outside the KVB that could be linked to the Nya-Ngezie Group, lying in the northwestern part of the Kivu Lake.

The K5 unit is associated to the post-Kibaran granites. The Banji Group of the Ubendian Belt could possibly be linked to this K5 unit (table I).

The main tectono-magmatic events (table II)

Owing to numerous studies all over the Kibaran Orogens since the beginning of the 20 th century, there is neither a coherent nomenclature for the three belts, nor for their several parts.

Each author has developed his own specific tectono-magmatic nomenclature with respect to local observations, which led to some confusion. The problem can exemplarily be shown for the discrepancies concerning the tectonic events in the Kivu area: the D1 and D2 tectonic events of [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF] correspond to the D2 of [START_REF] Rumvegeri | Etudes lithostratigraphique et structurale du Précambrien de la région de Bunyakiri (Kivu, Zaire); modèle d'évolution géodynamique de la chaine Kibarienne en Afrique centrale et orientale[END_REF]. On the other hand, the D1 of [START_REF] Blès | Etude photo-interprétative et reconnaissance géologique et structurale de la zone exclusive de recherches Masisi-Saké[END_REF] is quite similar to the D1 of [START_REF] Klerkx | Granitoides Kibariens précoces et tectonique tengentielle au Burundi: magmatisme bimodal lié à la distension crustale[END_REF] and different from the D1 of [START_REF] Rumvegeri | Etudes lithostratigraphique et structurale du Précambrien de la région de Bunyakiri (Kivu, Zaire); modèle d'évolution géodynamique de la chaine Kibarienne en Afrique centrale et orientale[END_REF]. Taking into account ages, direction and tectonic stress, eleven tectonic events have been distinguished throughout the Kibaran-Burundian belts (table II). In order to provide a coherent and common chronology for the whole series linked to the Kibaran-Burundian Orogen, each tectonic event has been renamed in the final list. From the earliest to the latest events we have listed: Dx, D1-1, D1-2, D1-3, D2-1, D2-2, D2-3, D2-4, D3-1, D3-2, and D3-3. The D4 tectonic event is associated to the pan-African tectonic events.

Dx events predate the sediment deposition. They are ascribed to the basement tectonic framework and have various directions.

D1-1 structures are characterised by an E-W trend and could be related to the opening of oceans, particularly to the K01 (KAB aulacogen). D1-2 structures show a NNE-SSW trend in the southern KIB, and are E-W in the KVB (Elila Belt). They are associated to a collisional event in these areas. D1-3 is a tectonic event linked to a post tectonic extensive regime.

D2-1 (NNE-SSW trend), D2-2 (NNW-SSE trend), D2-3 (E-W trend), and D2-4 (NW-SE trend) are associated to the folding and fracturing of the K2 basins. D2-1 is an extensional event associated to the opening of K2 basins. D2-2 and D2-3 are related to the folding of these basins.

The D2-3 event is well exposed in three E-W bands: the Luhule-Mobissio band to the North, the Rwate-Bilati band to the NW of the Kivu Lake and the Shabunda-Nzibira band to the SW of the Kivu Lake. The Shabunda-Nzibira structure is clearly a pop-up structure, in which the D2-2 structures are refolded by D2-3 folds. Relationships between the various D2 deformations are not clearly understood.

D3-1 with an E-W trend corresponds to the folding and metamorphism of the Bugarama Group (K3). D3-2 has an E-W to NW-SE trend is associated to the folding of the Nya-Ngezie Group (K4), while D3-3 shows NW-SE strike slips and thrusting to the SW of the D2-2 structures of the Nya-Ngezie Group. These NW-SE striking faults are largely developed all over the Northern KAB and KVB.

D4 with an N-S trend is associated with the Neoproterozoic post-orogenic magmatic event and to the opening of the Neoproterozoic Itombwe half graben.

Noticeably, there are similarities in orientation of the D1-1, D2-3, and D3-1 structures.

The same applies for D2-4 and D3-2 and D3-3. In the past [START_REF] Cahen | Géologie du Congo belge[END_REF], every tectonic direction was related to a single tectonic event, which became much more complex since the widespread application radiometric dating.

Conjunction between the main tectonic events and the lithostratigraphic units generated at least five main unconformities (Un1 to Un5). Un1 between the basement and unit 1 is supposed but not observed. However, there is an unconformity between the Bilati (Kv2) and the Kibalian basement. Un2 corresponds to the "Luemba unconformity" underlain by the Luemba conglomerate. Further occurrences of the Un2 are at the western flank of the Luemba synclinorium. Un3 corresponds to the unconformity between the Kv2 and Kv3 units and is yet only recognised on the Landsat images by [START_REF] Chorowicz | Apport géologique des images MSS Landsat du secteur autour du lac Kivu (Burundi, Rwanda and Zaire)[END_REF]. Un4 corresponds to the "Mt. Kamashuli unconformity" found in the Nya-Ngezie area [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF], whereas the "Nya-Kasiba unconformity" at the base of the Itombwe syncline is a part of the Un5 group [START_REF] Villeneuve | Mise en évidence d'une discordance angulaire majeure dans les terrains précambriens du Nord du synclinal de l'Itombwe (région du Kivu, République du Zaïre)[END_REF]. Despite several attempts, unconformities evidenced in the KAB have not yet been correlated to those of the KVB [START_REF] Villeneuve | Les sillons plissés du Brundien supérieur dans la chaine Kibarienne d'Afrique centrale[END_REF][START_REF] Villeneuve | Apports de l'imagerie spatiale à la résolution des structures géologiques en zone équatoriale: exemples du Précambrien au Kivu (Congo Oriental)[END_REF].

Such confusions also exist in the chronology of the granitic intrusions. Despite the first classification of Cahen et al. (1979), there are some large discrepancies between different authors and different countries. Since [START_REF] Blaise | Note sur les differentiations de certains batholites granitiques du Kivu[END_REF] it is known that granitic batholiths, like the Gondo Ya Bushema, cropping out west of the Kivu Lake, are composite and may include several intrusions of various ages. Blés (1972) notes that accordance between the magmatic batholith and host structure does not necessarily indicate a synkinematic emplacement. The Kasika granite provides a good example (see above). On the other hand, the chronology of magmatic events is mainly based on radiometric data, although there are some discrepancies depending on the applied radiometric method. The best example concerns the "arena granites" of western Uganda, of which the Chitwe granite was dated by the Rb/Sr at 1146 ± 40 Ma [START_REF] Vernon-Chamberlain | Age and isotope studies on the "arena" granites of SW Uganda[END_REF]. The same rock dated by the U-Pb method on zircon yielded an age of 1568 ± 23 Ma [START_REF] Buchwaldt | Crustal age domains in the Kibaran belt of SW Uganda: Combined zircon geochronology and Sm-Nd isotopic investigation[END_REF]. Similar results were found in the adjacent arena granites. Tables I andII show the main granitic bodies already dated in the region. No specific age clusters can be noted.

The main metamorphic events

The development of the metamorphic events related to the Kibaran Orogen is beyond the scope of this paper. Some of them are linked to the granitic intrusions or to the tectonic events. However, their grade of deformation is not correlated to their age. Metamorphic aureoles are present in every unit and the metamorphism could be more intense in the K3 than in the K1. An important period of "contact metamorphism" is related to the post collisional G4 granites. The sizes of metamorphic aureoles vary from hectometre to several kilometres away from the granitic massifs. The six main metamorphic events listed in table II will be developed elsewhere.

The main orogenic cycles

Considering the mentioned problems, we attempt to reconcile these local scales in table II.

Five main "tectono-sedimentary cycles" including basin opening, sediment deposition and tectono-magmatic events, have been considered.

-The first cycle (Cy1) includes all formations belonging to the unit K1, which is terminated by the 1375 Ma Kibaran event [START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF]. In the KAB it is represented by relict of E-W structures such as the Mugombwa anticline [START_REF] Gérards | L'anticlinal de Mugombwa (Rwanda): un exemple de discordance majeure entre le Burundien et son socle[END_REF] or the Rutunga structure [START_REF] Nzojibwami | The west Mugere suprecrustal complex (Bujumbura): Evidence of an ancient basement complex remobilised during the Kibaran orogeny[END_REF]). An extensive tectonic regime is considered in the KAB, meanwhile in the KIB and KVB this cycle seems to be ended by a compressive tectonic event.

-The second cycle (Cy2) began by accumulation of sedimentary deposits in N-S elongated trenches delineated by [START_REF] Villeneuve | Les sillons plissés du Brundien supérieur dans la chaine Kibarienne d'Afrique centrale[END_REF]. According to [START_REF] Blès | Etude photo-interprétative et reconnaissance géologique et structurale de la zone exclusive de recherches Masisi-Saké[END_REF], Villeneuve (1983), and [START_REF] Klerkx | Granitoides Kibariens précoces et tectonique tengentielle au Burundi: magmatisme bimodal lié à la distension crustale[END_REF] this could be linked to several N-S elongated basins intruded by large magmatic bodies inducing tangential isoclinal folds parallel to the bedding and inferred to the lower deposits (D2-1) during the extensional regime. These granites display several ages between 1360 and 1250 Ma. A set of compressive tectonic events (D2-2, D2-3, and D2-4) with various trends occurred between 1200 and 1180 Ma accompanied by several granitic intrusions (G2 or GR3). Thrust and strike-slip faults were commonly associated to the folds [START_REF] Theunissen | Considerations preliminaires sue l'evolution tectonique du «Burundien» au Burundi[END_REF][START_REF] Theunissen | Les principaux traits de la tectonique Kibarienne au Burundi[END_REF][START_REF] Klerkx | Granitoides Kibariens précoces et tectonique tengentielle au Burundi: magmatisme bimodal lié à la distension crustale[END_REF][START_REF] Klerkx | Crustal Evolution of the Northern Kibaran Belt, eastern and central Africa[END_REF]. The KVB has a quite similar evolution. A similar extensional regime in the KIB is terminated by a younger compressive tectonic event (1079 ± 14 Ma).

-The third cycle (Cy3) began with the deposition of the Bugarama Group after ca. 1180 Ma and was terminated by the D3-1 tectonic event reported by [START_REF] Villeneuve | Le Précambrien du sud du lac Kivu (République du Zaïre)[END_REF] prior to the deposition of the Nya-Ngezie Group (post ca. 1120 Ma). The Masisi through is oriented N-S while the latest tectonic event exhibits E-W to WNW-ESE structures [START_REF] Blès | Etude photo-interprétative et reconnaissance géologique et structurale de la zone exclusive de recherches Masisi-Saké[END_REF]. This is likely the case for the Bugarama Basin. The meridional alignment of these two basins has to be noted.

Up to now these basins are limited to the eastern part of KVB. This means: either these terranes

are not yet evidenced elsewhere or they are limited to the rift zone and should be interpreted as a basin opened in the middle part of the KVB and KAB assemblage.

-The fourth cycle (Cy4) is dated between ca. 1120 and ca. 1079 Ma and corresponds to the deposition and folding of the Nya-Ngezie Group. The D3-2 tectonic events are linked to the main E-W to NW-SE hectometric to kilometric folds of the Nya-Ngezie area, and to the large NW-SE shear zones crossing the KVB and the KAB. Very few sedimentary deposits are ascribed to this cycle. The latter is not consistent with a D3-1 doming followed by an erosional stage that would have been able to feed such E-W oriented basins. However, granitic intrusions, consistent with this tectonic event, are recorded in the KIB and in Tanzania.

-The last cycle (Cy5) corresponds to the "post Kibaran" magmatic event as proposed by several authors. The intra-cratonic intrusions were emplaced between ca. 975 and ca. 920 Ma (mean age around 960 Ma) and provide the main metallogenic occurrences, particularly in tin, tungsten, and coltan minerals. Meanwhile, the sediments of the Lindian and Malagarasian formations were deposited on both sides of the Kibaran-Burundian Belt. The exact time relationships between the NW-SE D3-3 structures and the post Kibaran-Burundian granites setting remain unknown. However, according to [START_REF] Dewaele | Geological setting and timing of the cassiterite vein type mineralization of the Kalima area (Maniema, Democratic Republic of Congo)[END_REF] a Late Kibaran magmatic event occurred in the Maniema province (western KVB) between 1024 ± 5.5 Ma and 993 ± 1 Ma.

It could be linked to an N-S shrinking that occurred before ca. 950 Ma, and thus, may be the trigger for the post orogenic granitic intrusions.

Geodynamical consequences (Table II)

Two opposite geodynamic models prevailed for a long time: i) the "mobile plate tectonic model" with oceanic subduction and continent / continent collision supported by [START_REF] Kokonyangi | U-Pb zircon geochronology and petrology of granitoids from Mitwaba (Katanga, Congo): implications for the evolution of the Mesoproterozoic Kibaran belt[END_REF] in Katanga and by [START_REF] Rumvegeri | Le Précambrien de l'Ouest du lac Kivu (Zaïre) et sa place dans l'évolution géodynamique de l'Afrique centrale et orientale[END_REF] in the Kivu area; ii) the intra-continental (ensialic) model supported by the [START_REF] Klerkx | Granitoides Kibariens précoces et tectonique tengentielle au Burundi: magmatisme bimodal lié à la distension crustale[END_REF][START_REF] Klerkx | Crustal Evolution of the Northern Kibaran Belt, eastern and central Africa[END_REF] and others in Rwanda and Burundi.

Owing to the lack of consistent radiometric dating, both models are considered as contemporaneous. However, the unique SSW-NNE trend led every author to consider his own conclusions as valid for the whole orogen. Considering these conclusions as representative of the local environment, we are looking for a "coordinated geodynamic model" taking into account that every local hypothesis is consistent. Table II presents the main characteristics of each cycle and their supposed geodynamic model only consistent for the KVB and KIB. Nine stages (a, b, c, d, e, f, g, h, i) have been distinguished in close relationship with the main orogenic cycles. Kokonyangi et al. (2006) admitted a plate tectonic model operating before the D1-2 tectonic event (1380 Ma) and an intra-basinal regime between 1380 Ma (or 1375 Ma) and the D2-2 tectonic event in the KIB. According to [START_REF] Debruyne | Regional geodynamic context for the Mesoproterozoic Kibara belt (KIB) and the Karagwe-Ankole belt: Evidence from geochemistry and Isotopes in the KIB[END_REF], the slab was subducted to the east underneath the Bangweulu Block, although no Mesoproterozoic rocks related to an orogenesis have been found. The latter was followed by the post collisional regime coeval with the intrusions of tin bearing granitoids around 960 Ma. This geodynamic model was supported by Kokonyangi has been revised by [START_REF] Debruyne | Regional geodynamic context for the Mesoproterozoic Kibara belt (KIB) and the Karagwe-Ankole belt: Evidence from geochemistry and Isotopes in the KIB[END_REF]. These authors considered a very long collisional stage between 1375 Ma and 1000 Ma that is highly questionable. A similar model was also considered for the KVB during cycle 1 by [START_REF] Rumvegeri | Lithostratigraphie et evolution structurale de la chaine Kibarienne à l'Ouest du lac Kivu (Zaire)[END_REF][START_REF] Rumvegeri | Le Précambrien de l'Ouest du lac Kivu (Zaire) et sa place dans l'évolution Géodynamique de l'Afrique centrale et orientale[END_REF]. Recent geochemical investigations on the Bunyakiri gneiss of the Lushasha Complex by Mugaruka Bibentyo et al.

(2015) favoured an island arc setting which could be linked to this first geodynamic event (a and b, table II). The Lushasha Complex and the Elila Formation could be involved in this "subduction / collision" model although there are no witnesses of classical elements as ophiolite obduction, suture zones, and volcano-magmatic arcs to support a plate tectonic model ascribed to Cy1 as underlined by Liégeois (pers. comm.). Consequently, the slab vergence is unknown. In contrast, such a model is excluded by [START_REF] Klerkx | Granitoides Kibariens précoces et tectonique tengentielle au Burundi: magmatisme bimodal lié à la distension crustale[END_REF], [START_REF] Tack | The 1375 Ma "Kibaran event" in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime[END_REF][START_REF] Fernandez-Alonso | The Mesoproterozic Karagwe-Ankole belt (formerly the NE Kibara belt): The result of prolonged extensional intracratonic basin development punctuated by two short-lived farfield compressional events[END_REF] in the KAB, where the sedimentary deposits are continuous during the Cy1 and Cy2.

Thus, an extensional regime is favoured by them, from ca. 1400 Ma to ca. 1180 Ma. After this first collision in the KIB and KVB, an extensive regime is hypothesised everywhere during Cy2 (c, table II). The latter was terminated during a major tectonic event (d, table II). Then, the intracrustal evolution of the Bugarama and Nya-Ngezie groups (Cy4 and Cy5) are illustrated in table II (e, f, g, h). After this last episode, a general tectonic reactivation of N-S elongated structures gave way to a large amount of post tectonic granitic bodies (Cy5) illustrated in table II (i).

Although there are several tectono-metamorphic cycles, all are included in the Kibaran Orogeny.

A reconciling hypothesis

The synopsis visualised in table II allows us to launch a new hypothesis in order to reconcile the opposite geodynamic models proposed in the KIB / KVB against the model proposed in the KAB. A model similar to that of Dewey (1968) for the Atlantic Ocean including the opening of three aulacogens fits with our considerations. Such a model considers an aborted branch, and a large opening of the two other branches. Before the closure of the two latter branches convergence processes lead to the formation of a mountain belt.. This hypothesis relies on the Wichita and Marathon-Oklahoma rifts capped by the Variscan Ouachita Belt (King, 1975;[START_REF] Zolnai | NG5: (field sample 2-443a) Kamanyola Formation: N 2° 41' 86.0" / W 28° 57' 22.1" NG6: (field sample 2-483) Kashenie[END_REF] in the southern part of the USA. This model seems to be the best solution to explain the different models between the KIB / KVB versus the KAB. The KAB could be an analogue of the aborted Proterozoic to Palaeozoic "Marathon-Oklahoma" aulacogen meanwhile the KIB and KVB could be compared to the Variscan Ouachita Belt. In our opinion this hypothesis deserves to be carefully examined.

Relationships between the modern rift structures and the Proterozoic basement.

A close relationship between the N-S pan-African troughs and the modern rift structures in the Kivu area has already been discussed by Villeneuve (1983b). The existence of a late Kibaran N-S trough located between the pan-African Itombwe trough and the Kivu Rift structures is a new possibility. This suggests that the ancestor of the modern rift is not linked to the pan-African period but is likely older and of potential Late Mesoproterozoic age.

Concluding remarks

In conclusion the new U-Pb age determinations on detrital zircons from six samples of the Bugarama and Nya-Ngezie groups have:

1) Shown the necessity to establish two new belts that occurred between the folding of the late Kibaran (1250-1200 Ma) and the intrusions of the G4 tin bearing granites (ca. 970 to ca. 920 Ma). The deposition of the lower Bugarama Group took place between 1207 ± 28 and 1121 ± 14 Ma. Meanwhile the upper Nya-Ngezie Group was deposited between 1121 ± 14 and 1111 ± 38 Ma. Inherited zircon grains from these two groups indicate several source rocks and noticeably sediments coming from the erosion of remote (or recycled) Archaean or Palaeoproterozoic materials.

2) Improved our understanding on the evolution of the Kivu area and allow us to decipher a KVB (Kivu Belt) different from the KAB (Karagwe-Ankolean Belt) and from the KIB (Kibaride Belt), in which the Bugarama and Nya-Ngezie groups are lacking.

3) Proposed the abandonment of the classical Burundian trilogy (Lower, Middle and Upper Burundian) which is still a matter of debate. For [START_REF] Rumvegeri | Tectonic significance of Kibaran structures in Central and Eastern Africa[END_REF] the Lower and Middle Burundian correspond to our Unit II (K2) and the Upper Burundian to our Units III (K3) and IV (K4) meanwhile for others, the Lower, Middle and Upper Burundian refer to formations included within unit II (K2).

These new data allows us to suggest a large set of correlations between the KAB and the KIB and even with the associate Kibaran Belts such as the Ubendian Trough of Tanzania. These correlations exposed in table I allow us to propose: 1) A new geological sketch map of the KAB and KVB areas (figure 1).

2) The distinction of four main lithostratigraphic units in the KVB, KAB, and KIB (table I).

3) The occurrence of eleven tectonic events (table II) between the D1-1 (pre-1380 Ma) and the D3-3 (around 1020 Ma) tectonic events.

4) The distinction of five tectono-sedimentary cycles (Cy1 to Cy5) associated to these tectonic events and to numerous magmatic and metamorphic events (table II). In addition nine (a to i) geodynamic stages are proposed in table II. A classical model of an active margin setting is accepted for the KVB and the KIB coeval with an "aulacogen" in the KAB (a and b). Then, several basins opened and closed from ca. 1360 to ca. 1050 Ma (c to i).

5) An additional contribution is to propose a hypothesis for reconciling the opposite geodynamic model between KIB / KVB and the KAB. Our hypothesis is based upon a "three branch model" of aulacogen opening followed by the closure of two of them by collisional processes in the KVB and the KIB, in their first stage of evolution. Consequently, the third branch (KAB) is considered as an aborted rift (aulacogen). This hypothesis is inspired by the model of Neoproterozoic to Palaeozoic aulacogens (i.e.: Marathon Aulacogen) of North America limited to the south by the Variscan belts (Ouachita Belt).

6) Another hypothesis considers the central part of the KVB and KAB assemblage occupied by

the "Great Lakes" as a very old weakness zone which was successively reactivated in a narrow meridional zone. The latter also hosts the Late Mesoproterozoic Masisi and Bugarama basins, the Neoproterozoic anorogenic alkaline complex, the Itombwe through, and finally, the Neogene East African Rift. Analogues of the modern rift could be initiated at the end of the Kibaran Orogeny.

Of course, this simplified synthetic view has to be improved by more field and radiometric data, especially in the very poorly studied Kivu area where the main investigations have been performed before the year 2000. Many questions are unsolved, noticeably the relationships between the tectonic, magmatic, and metamorphic events. We are expecting that this synthetic view provides an interesting "working tool" for further studies.

Aknowledgements

We acknowledge the two reviewers Denis Thièblemont and Jean-Paul Liégèois who strongly improved this paper and also thank to Oceane Stchetinine for the drawing of tables.

Figure Captions

Table I -Correlations throughout the Kibaran Belts, from Katanga (SE Congo) to Uganda.

Legend: Kv (Kv1 to Kv4) = lithostratigraphic units in the KVB, Ki (Ki1 to Ki4) = Lithostratigraphic units in the Kibaride belt (KIB). K1 to K5 = Common Lithostratigraphic units for the Kibaran Orogen, Un1 to Un5 = Major unconformities. Kai. gr. = Kiaora Group, Nzilo gr. = Nzilo Group, Haka.gr. = Hakansson Group, Lub.gr. = Lubudi Group, Banji Group = Banji Group, Luiko gr. = Luiko Group. Wak.T. = Wakole Terranes, It. gr. = Itiaso Group, Ubend. = Ubendian basement, Ukiga gr. = Ukiga Group, Rug.gr = Rugezi Group, Cyo.gr. = Cyohoha Group, Pin.gr. = Pindura Group, Gik.gr = Gikoro Group, Tanz.bas = Tanzanian basement, Buk.gr. = Bukoba Group, Ruv.gr = Ruvubu Group, Muy.gr. = Muyaga Group, Igara bas. = Igara basement,

Table II-Synopsis of the Kibaran Orogen evolution including tectonostratigraphic cycles, tectonic, granitic and metamorphic events. Cartoons of the geodynamic evolution of the Kibaran Orogen through time

Legend: K/Cy = tectonostratigraphic cycles, Un = major unconformities, D = tectonic events, G = main granitic events, M = Main metamorphic events (explanation in text), Yellow circles = Main stages of the geodynamic evolution (see explanations in text). 1 -Extensional tectonic regime, 2 -compressional tectonic regime.

Figure 1 :Figure 2 -

 12 Figure 1: Geological sketch map of the KAB (Kivu Belt) and KVB (Karagwe-Ankole Belt)

Figure 3 -

 3 Figure 3 -Sedimentological marks of the Nya-Ngezie group.

Figure 4 -

 4 Figure 4 -Diagram with the mean ages of inherited zircons in the Bugarama and Nya-

Figure 5 -

 5 Figure 5 -Northern (CD) and southern (AB) geological sections across the KVB and the

  NG1 to NG6 samples dated by detrital zircons and located in figs 2 and 4.

  U-Pb-Th data of zircon from sample NG1, n = 90 of 208 measured zircon grains (90-110 % conc.), quartzitic sandstone with ripple marks, South Kivu Province, DR Congo U-Pb-Th data of zircon from sample NG3, n = 106 of 152 measured zircon grains (90-110 % conc.), quartzite, South Kivu Province, DR Congo

		Tab. 2: 207 Pb Number (cps) NG1-seq1-a01 101687 147 U a (ppm) (ppm) Pb a 59 NG1-seq1-a02 1859 6 2 NG1-seq1-a03 18020 54 11 NG1-seq1-a04 156639 251 69 NG1-seq1-a05 182203 260 74 NG1-seq1-a06 87796 274 64 NG1-seq1-a07 8954 13 6 NG1-seq1-a08 119328 187 76 NG1-seq1-a09 35525 163 26 NG1-seq1-a10 162667 689 101 0.22 Th c U 0.83 20181 0.33517 2.0 5.17342 2.5 0.11195 1.5 0.81 1863 33 1848 22 1831 27 206 Pb 206 Pb e 2 σ 207 Pb e 2 σ 207 Pb e 2 σ rho 206 Pb 2 σ 207 Pb 2 σ 207 Pb 2 σ 204 Pb 238 U % 235 U % 206 Pb % 238 U (Ma) 235 U (Ma) 206 Pb (Ma) conc % 102 1.80 2303 0.21367 5.7 2.41641 9.2 0.08202 7.2 0.62 1248 65 1247 68 1246 140 100 0.46 1334 0.19529 3.3 2.40667 3.9 0.08938 2.0 0.85 1150 35 1245 28 1412 39 81 0.53 1158 0.24225 3.2 3.97488 3.5 0.11900 1.4 0.91 1398 40 1629 29 1941 25 72 0.64 327 0.22729 2.3 3.54657 3.0 0.11317 1.9 0.77 1320 28 1538 24 1851 34 71 1.02 4489 0.19337 2.2 3.02394 2.5 0.11342 1.2 0.88 1140 23 1414 19 1855 22 61 1.46 8228 0.32395 2.4 4.93552 3.8 0.11050 3.0 0.64 1809 39 1808 33 1808 54 100 0.84 15957 0.33775 1.7 5.43328 2.3 0.11667 1.5 0.75 1876 28 1890 20 1906 28 98 0.92 6515 0.13681 2.6 1.98351 2.8 0.10515 1.0 0.93 827 20 1110 19 1717 19 48 2198 0.12796 3.0 1.97985 3.6 0.11222 2.0 0.83 776 22 1109 25 1836 37 42 NG1-seq1-a11 106369 157 57 0.44 32995 0.33385 2.4 5.30820 2.7 0.11532 1.1 0.91 1857 40 1870 23 1885 20 99 NG1-seq1-a12 98063 168 68 0.89 86597 0.33703 2.1 5.33121 2.4 0.11473 1.2 0.87 1872 34 1874 21 1876 21 100 NG1-seq1-a13 50761 119 20 0.75 9242 0.12093 7.6 1.85275 7.8 0.11112 1.5 0.98 736 53 1064 53 1818 27 40 NG1-seq1-a14 80989 205 69 1.02 21580 0.28953 1.8 4.32253 2.1 0.10828 1.1 0.85 1639 26 1698 17 1771 20 93 NG1-seq1-a15 24152 104 21 1.06 4401 0.17050 3.7 2.66590 4.0 0.11340 1.5 0.93 1015 34 1319 30 1855 27 55 NG1-seq1-a16 50322 88 34 0.83 11153 0.32617 2.5 5.18201 2.9 0.11523 1.5 0.85 1820 40 1850 25 1883 28 97 NG1-seq1-a17 121851 226 83 0.71 32440 0.31181 2.0 4.86319 2.2 0.11312 0.9 0.90 1750 31 1796 19 1850 17 95 NG1-seq1-a18 61565 216 57 0.85 11671 0.23816 2.2 3.66578 2.5 0.11163 1.3 0.86 1377 27 1564 20 1826 24 75 NG1-seq1-a19 95454 202 67 0.39 65968 0.32835 3.3 5.19702 3.4 0.11479 1.0 0.96 1830 53 1852 30 1877 18 98 NG1-seq1-a20 74903 139 52 0.60 66424 0.32992 2.1 5.17822 2.6 0.11383 1.4 0.83 1838 34 1849 22 1861 26 99 NG1-seq1-a21 36131 166 52 2.39 16241 0.21092 1.8 2.39194 2.2 0.08225 1.3 0.81 1234 20 1240 16 1251 25 99 NG1-seq1-a22 60840 173 45 1.04 27838 0.21112 3.4 3.35069 3.6 0.11511 1.0 0.96 1235 39 1493 28 1882 18 66 NG1-seq1-a23 34598 88 27 0.99 7773 0.25444 2.4 3.96982 2.8 0.11316 1.4 0.87 1461 32 1628 23 1851 25 79 NG1-seq1-a24 25158 185 23 0.38 5752 0.12481 2.2 1.46834 2.7 0.08532 1.6 0.81 758 16 917 16 1323 31 57 NG1-seq1-a25 45534 93 35 0.70 12776 0.32879 1.8 5.23896 2.3 0.11557 1.4 0.79 1832 29 1859 20 1889 25 97 NG1-seq1-a26 101955 210 83 0.78 89032 0.33545 2.0 5.35590 2.3 0.11580 1.1 0.88 1865 33 1878 20 1892 20 99 NG1-seq1-a27 22042 46 18 0.85 19115 0.33161 2.1 5.34542 2.8 0.11691 1.9 0.75 1846 34 1876 24 1909 33 97 NG1-seq1-a28 40474 103 35 0.77 6566 0.29684 2.9 4.74559 3.3 0.11595 1.7 0.87 1676 42 1775 28 1895 30 88 NG1-seq1-a32 99433 317 71 0.85 14373 0.16637 3.3 2.54221 3.6 0.11082 1.3 0.93 992 30 1284 26 1813 24 55 NG1-seq1-a33 13270 157 14 0.92 819 0.07307 4.5 1.16918 5.2 0.11605 2.6 0.87 455 20 786 29 1896 46 24 NG1-seq1-a34 72431 239 69 0.92 22600 0.25370 1.8 3.96518 2.0 0.11336 0.9 0.90 1458 23 1627 16 1854 16 79 NG1-seq1-a35 31571 120 37 1.11 1299 0.26687 2.5 4.09899 2.7 0.11140 1.2 0.90 1525 34 1654 22 1822 21 84 NG1-seq1-a36 62342 219 67 0.93 32588 0.27155 2.0 4.25175 2.2 0.11356 1.0 0.90 1549 28 1684 19 1857 17 83 NG1-seq1-a37 49620 280 50 0.69 7645 0.16718 2.1 2.63867 2.4 0.11447 1.3 0.85 997 19 1311 18 1872 23 53 NG1-seq1-a38 86579 349 109 0.94 9710 0.27812 1.6 4.36496 1.9 0.11383 1.0 0.85 1582 23 1706 16 1861 18 85 NG1-seq1-a39 129139 333 124 1.00 1271 0.31348 1.8 4.82755 2.0 0.11169 0.8 0.91 1758 28 1790 17 1827 14 96 NG1-seq1-a40 3837 66 4 0.89 4590 0.05974 3.3 0.67261 4.7 0.08165 3.3 0.71 374 12 522 19 1237 65 30 NG1-seq1-a41 39720 157 41 0.94 36933 0.22975 3.5 3.44979 3.8 0.10890 1.4 0.93 1333 43 1516 30 1781 26 75 NG1-seq1-a42 23583 52 22 1.09 20359 0.33360 1.9 5.21262 2.4 0.11332 1.5 0.78 1856 31 1855 21 1853 27 100 NG1-seq1-a43 67720 243 57 0.99 5993 0.19661 2.0 3.04559 2.2 0.11235 0.9 0.91 1157 22 1419 17 1838 17 63 NG1-seq1-a44 21847 72 24 1.41 13393 0.25879 2.4 4.07625 2.8 0.11424 1.4 0.86 1484 32 1650 23 1868 26 79 NG1-seq1-a45 12614 90 9 1.11 2264 0.08417 3.8 1.26167 4.5 0.10872 2.4 0.84 521 19 829 26 1778 44 29 NG1-seq1-a46 69799 408 48 0.60 6839 0.10385 3.1 1.55236 3.2 0.10841 1.0 0.95 637 19 951 20 1773 18 36 NG1-seq1-a47 25507 46 20 1.13 22170 0.34772 2.0 5.57967 2.7 0.11638 1.8 0.75 1924 33 1913 23 1901 32 101 NG1-seq1-a48 59595 139 42 0.81 31383 0.25787 4.5 4.19944 4.6 0.11811 1.2 0.96 1479 60 1674 39 1928 22 77 NG1-seq1-a49 18179 67 17 0.71 4843 0.22317 2.1 2.62356 2.5 0.08526 1.4 0.83 1299 24 1307 19 1321 27 98 NG1-seq1-a50 52550 111 47 2.16 46991 0.30391 1.8 4.74645 2.0 0.11327 0.9 0.89 1711 27 1775 17 1853 17 92 NG1-seq1-a51 18577 44 16 1.32 16466 0.27631 2.8 4.35979 3.5 0.11444 2.0 0.81 1573 40 1705 29 1871 36 84 NG1-seq1-a52 37294 80 26 1.01 13261 0.25542 2.0 3.98389 2.2 0.11312 0.9 0.92 1466 27 1631 18 1850 16 79 NG1-seq1-a53 65273 509 65 0.76 2192 0.12158 2.7 1.80916 3.0 0.10792 1.4 0.89 740 19 1049 20 1765 25 42 NG1-seq1-a54 34910 75 22 1.16 11924 0.21532 3.2 3.32866 3.4 0.11212 1.1 0.94 1257 36 1488 27 1834 20 69 NG1-seq1-a55 21378 120 16 0.81 2955 0.12793 3.8 1.76220 4.3 0.09990 2.0 0.89 776 28 1032 28 1622 37 48 NG1-seq1-a56 49575 93 33 0.53 44107 0.32567 2.7 5.11080 3.0 0.11382 1.4 0.89 1817 42 1838 26 1861 25 98 NG1-seq1-a57 38018 86 28 0.95 15609 0.26251 2.0 4.15298 2.4 0.11474 1.3 0.83 1503 26 1665 20 1876 24 80 NG1-seq1-a58 28553 50 20 0.97 16060 0.33986 2.3 5.29410 2.7 0.11298 1.5 0.84 1886 38 1868 24 1848 27 102 NG1-seq1-a59 25041 58 24 1.56 7553 0.32611 2.3 5.02547 3.0 0.11177 2.0 0.76 1819 37 1824 26 1828 36 100 NG1-seq1-a60 58544 114 49 1.23 51336 0.33895 2.4 5.38229 2.9 0.11517 1.6 0.83 1882 39 1882 25 1883 29 100 NG1-seq2-b01 78072 97 28 0.49 26468 0.25467 2.7 4.07760 2.9 0.11613 1.0 0.94 1463 35 1650 24 1897 18 77 NG1-seq2-b02 14627 36 9 0.48 17592 0.23184 2.5 2.68214 3.4 0.08391 2.4 0.72 1344 30 1324 26 1290 46 104 NG1-seq2-b03 142723 170 60 0.36 25299 0.32923 2.3 5.22546 2.6 0.11511 1.2 0.89 1835 37 1857 22 1882 21 98 NG1-seq2-b04 52276 172 48 1.43 3950 0.19840 2.2 2.57261 2.6 0.09405 1.5 0.83 1167 23 1293 19 1509 28 77 NG1-seq2-b08 232407 516 150 0.49 8852 0.27796 1.9 4.24789 2.1 0.11084 0.9 0.90 1581 26 1683 17 1813 17 87 NG1-seq2-b09 91682 120 48 0.80 25846 0.33750 2.2 5.32428 2.5 0.11442 1.2 0.88 1875 36 1873 21 1871 21 100 NG1-seq2-b10 167861 276 94 0.51 151598 0.31251 1.8 4.81645 2.2 0.11178 1.2 0.83 1753 28 1788 18 1829 22 96 NG1-seq2-b11 151336 209 82 0.81 134218 0.33008 2.2 5.18368 2.6 0.11390 1.5 0.82 1839 35 1850 22 1863 27 99 NG1-seq2-b12 35715 183 22 0.62 3929 0.11088 6.1 1.28207 6.4 0.08386 1.7 0.96 678 40 838 37 1289 33 53 NG1-seq2-b13 8379 24 7 1.18 2100 0.21879 2.6 2.48003 3.4 0.08221 2.3 0.75 1275 30 1266 25 1251 44 102 NG1-seq2-b14 60110 78 37 1.37 52249 0.34156 1.9 5.47054 2.5 0.11616 1.6 0.77 1894 32 1896 22 1898 29 100 NG1-seq2-b15 22042 37 14 0.96 3254 0.30876 2.2 4.77678 3.2 0.11220 2.3 0.69 1735 34 1781 27 1835 42 95 NG1-seq2-b16 81186 118 43 0.54 40995 0.32369 2.0 4.95033 2.4 0.11092 1.4 0.83 1808 32 1811 21 1815 25 100 NG1-seq2-b17 123381 1412 72 0.07 1236 0.04355 2.8 0.53174 3.0 0.08855 1.0 0.94 275 8 433 11 1394 19 20 NG1-seq2-b18 41330 60 24 0.67 28496 0.33748 2.1 5.33153 2.3 0.11458 1.0 0.90 1875 34 1874 20 1873 18 100 NG1-seq2-b19 102818 145 59 0.97 28643 0.32779 2.3 5.19075 2.6 0.11485 1.1 0.90 1828 37 1851 22 1878 21 97 NG1-seq2-b20 72657 110 43 0.77 19073 0.32779 2.5 5.18363 3.0 0.11469 1.7 0.83 1828 40 1850 26 1875 30 97 NG1-seq2-b21 84725 123 51 0.90 30673 0.33881 3.9 5.40940 4.7 0.11579 2.6 0.84 1881 65 1886 41 1892 46 99 NG1-seq2-b22 62064 95 44 1.32 55216 0.34738 2.2 5.44526 2.8 0.11369 1.7 0.79 1922 36 1892 24 1859 31 103 NG1-seq2-b23 86502 147 53 0.76 898 0.29533 2.7 4.83420 3.0 0.11872 1.2 0.91 1668 40 1791 26 1937 22 86 NG1-seq2-b24 -------------------NG1-seq2-b25 35346 238 25 1.03 5545 0.07986 3.1 0.90156 3.2 0.08188 0.9 0.96 495 15 653 16 1243 18 40 NG1-seq2-b26 72230 147 42 1.10 12612 0.23082 3.2 3.61320 3.3 0.11353 0.7 0.98 1339 39 1552 27 1857 13 72 NG1-seq2-b27 106340 197 71 0.52 31317 0.34481 1.7 5.53855 2.0 0.11650 1.0 0.86 1910 29 1907 17 1903 18 100 NG1-seq2-b28 140179 358 112 0.95 5970 0.28342 2.0 4.44610 2.1 0.11378 0.7 0.94 1609 28 1721 18 1861 13 86 NG1-seq2-b29 103746 164 63 0.60 91059 0.33712 2.4 5.35144 2.8 0.11513 1.6 0.83 1873 38 1877 24 1882 28 100 NG1-seq2-b30 76975 149 62 1.52 6693 0.32513 2.9 5.12304 3.3 0.11428 1.6 0.87 1815 46 1840 29 1869 29 97 NG1-seq2-b31 80000 146 46 0.66 8991 0.27403 3.5 4.42950 4.2 0.11724 2.2 0.84 1561 49 1718 35 1915 40 82 NG1-seq2-b32 34033 104 36 1.05 5600 0.31315 2.0 4.91436 2.4 0.11382 1.4 0.83 1756 31 1805 21 1861 24 94 NG1-seq2-b33 16934 81 20 1.59 1558 0.17086 2.4 1.96425 3.9 0.08338 3.1 0.60 1017 22 1103 27 1278 61 80 NG1-seq2-b34 148030 325 114 0.41 25020 0.33167 2.7 5.25191 2.9 0.11484 1.1 0.93 1846 44 1861 25 1877 19 98 NG1-seq2-b35 59062 102 41 1.07 9639 0.32599 2.1 5.07283 2.5 0.11286 1.2 0.87 1819 34 1832 21 1846 22 99 NG1-seq2-b36 41730 101 37 0.88 12779 0.31879 2.2 4.92583 2.7 0.11206 1.6 0.80 1784 34 1807 23 1833 29 97 NG1-seq2-b37 270040 180 107 0.44 30431 0.51727 2.4 13.09566 2.9 0.18362 1.5 0.85 2688 54 2687 28 2686 25 100 NG1-seq2-b38 21815 32 15 1.14 9458 0.39017 2.2 6.21818 2.7 0.11559 1.5 0.83 2124 40 2007 24 1889 27 112 NG1-seq2-b39 57784 230 54 0.65 6410 0.22771 2.3 2.71941 2.7 0.08661 1.3 0.87 1323 28 1334 20 1352 25 98 NG1-seq2-b40 71385 163 37 0.51 10142 0.19247 5.3 2.97848 5.6 0.11223 1.5 0.96 1135 56 1402 43 1836 27 62 NG1-seq2-b44 77654 103 42 0.87 9457 0.33793 3.9 5.40584 4.3 0.11602 1.7 0.92 1877 65 1886 37 1896 30 99 NG1-seq2-b45 123322 147 59 0.96 108749 0.32579 2.4 5.14445 2.7 0.11452 1.3 0.88 1818 38 1843 23 1872 23 97 NG1-seq2-b46 26051 85 9 1.06 3980 0.08570 2.9 1.36436 3.3 0.11546 1.6 0.87 530 15 874 19 1887 29 28 NG1-seq2-b47 58933 68 26 0.78 54435 0.32594 2.1 4.92094 3.2 0.10950 2.4 0.65 1819 33 1806 27 1791 44 102 NG1-seq2-b48 44156 46 18 1.63 11783 0.27048 2.5 4.29497 2.8 0.11517 1.4 0.87 1543 34 1692 24 1882 25 82 NG1-seq2-b49 102364 123 42 0.93 9020 0.31139 1.9 4.90049 2.0 0.11414 0.7 0.94 1748 29 1802 17 1866 12 94 NG1-seq2-b50 33477 30 13 1.55 29147 0.32081 1.9 5.13210 2.1 0.11602 1.0 0.89 1794 29 1841 18 1896 17 95 NG1-seq2-b51 39850 33 14 0.85 15851 0.34831 2.0 5.65490 2.4 0.11775 1.3 0.83 1927 33 1925 21 1922 24 100 NG1-seq2-b52 31787 62 20 1.13 5896 0.29549 2.7 4.71685 3.4 0.11577 2.0 0.80 1669 40 1770 29 1892 36 88 NG1-seq2-b53 46977 48 20 1.32 8510 0.33728 2.3 5.35032 2.5 0.11505 0.9 0.94 1874 38 1877 22 1881 16 100 NG1-seq2-b54 17039 52 7 0.76 5491 0.13120 3.7 1.71920 4.1 0.09504 1.7 0.91 795 28 1016 27 1529 33 52 NG1-seq2-b55 155485 121 29 0.71 6565 0.21871 3.7 5.38556 3.8 0.17859 0.8 0.98 1275 43 1883 33 2640 13 48 NG1-seq2-b56 66931 70 22 1.36 7061 0.26409 2.0 4.12585 2.2 0.11331 1.0 0.90 1511 27 1659 18 1853 18 82 NG1-seq2-b57 168998 329 48 0.61 2928 0.13424 2.1 2.16483 2.2 0.11696 0.6 0.96 812 16 1170 15 1910 10 43 NG1-seq2-b58 65045 72 21 0.70 10261 0.27571 2.6 4.32254 2.8 0.11371 1.0 0.93 1570 37 1698 24 1860 19 84 NG1-seq2-b59 127198 117 33 0.42 50013 0.27177 2.3 4.31913 2.4 0.11527 0.9 0.93 1550 31 1697 20 1884 17 82 NG1-seq2-b60 315424 126 65 0.45 47249 0.46458 2.1 10.95351 2.3 0.17100 0.8 0.93 2460 43 2519 21 2567 14 96 NG1-seq3-c01 437132 987 158 0.26 2288 0.15391 2.9 3.43131 3.2 0.16169 1.4 0.90 923 25 1512 25 2473 24 37 NG1-seq3-c02 137103 260 77 1.02 25094 0.25286 2.3 3.95262 2.5 0.11337 1.1 0.90 1453 30 1625 21 1854 20 78 NG1-seq3-c03 82763 182 60 1.40 26542 0.27119 2.0 4.07432 2.3 0.10897 1.1 0.88 1547 27 1649 19 1782 20 87 NG1-seq3-c04 121088 208 82 0.99 35769 0.33313 2.5 5.23093 2.7 0.11388 1.0 0.93 1854 40 1858 23 1862 18 100 NG1-seq3-c05 111814 193 116 1.16 12340 0.54422 1.7 8.99510 1.9 0.11987 1.0 0.86 2801 38 2338 18 1954 17 143 NG1-seq3-c06 348352 286 139 0.79 157 0.33609 2.0 5.27100 2.4 0.11374 1.4 0.81 1868 32 1864 21 1860 26 100 NG1-seq3-c07 145837 931 110 0.12 3043 0.09124 2.3 1.39199 2.6 0.11065 1.1 0.91 563 13 886 15 1810 20 31 NG1-seq3-c08 69783 242 52 0.68 80511 0.20022 1.8 2.40994 2.0 0.08730 1.0 0.88 1176 19 1246 15 1367 18 86 NG1-seq3-c09 48626 137 29 1.09 6558 0.17348 4.4 2.74657 4.5 0.11482 1.1 0.97 1031 42 1341 34 1877 20 55 NG1-seq3-c10 10009 40 8 1.27 1559 0.16954 2.8 2.62396 3.3 0.11225 1.8 0.83 1010 26 1307 25 1836 33 55 NG1-seq3-c11 99174 167 68 1.23 88343 0.33074 2.1 5.15596 2.3 0.11306 1.0 0.90 1842 33 1845 20 1849 18 100 NG1-seq3-c12 103307 183 60 0.68 7225 0.29992 1.8 4.88445 1.9 0.11812 0.7 0.94 1691 27 1800 17 1928 12 88 NG1-seq3-c13 283504 296 126 0.81 10309 0.37347 1.7 8.62542 1.8 0.16750 0.5 0.96 2046 30 2299 16 2533 8 81 NG1-seq3-c14 94680 320 61 0.54 5766 0.17369 1.7 2.62855 2.0 0.10976 1.1 0.84 1032 16 1309 15 1795 20 58 NG1-seq3-c15 45699 179 31 0.79 4185 0.15240 2.8 2.38283 3.8 0.11340 2.5 0.75 914 24 1237 27 1855 45 49 NG1-seq3-c16 158880 302 112 0.58 113361 0.33054 3.0 5.32136 3.1 0.11676 0.8 0.96 1841 48 1872 27 1907 15 97 NG1-seq3-c20 146686 315 105 0.91 35265 0.28739 2.2 4.58091 2.5 0.11560 1.1 0.90 1628 32 1746 21 1889 19 86 NG1-seq3-c21 62237 234 42 0.89 8589 0.15532 2.9 2.42213 3.1 0.11310 1.1 0.93 931 25 1249 22 1850 20 50 NG1-seq3-c22 50187 154 37 0.93 6818 0.22113 2.8 3.40689 3.1 0.11174 1.3 0.91 1288 33 1506 25 1828 24 70 NG1-seq3-c23 21053 145 24 1.41 3818 0.12765 2.1 1.44264 3.0 0.08197 2.0 0.72 774 16 907 18 1245 40 62 NG1-seq3-c24 141185 572 104 0.75 9857 0.16214 1.8 2.52622 2.0 0.11300 1.0 0.88 969 16 1280 15 1848 18 52 NG1-seq3-c25 97114 297 64 0.72 10042 0.19637 3.0 3.16026 3.1 0.11672 0.7 0.97 1156 32 1448 24 1907 13 61 NG1-seq3-c26 108467 299 65 0.64 14278 0.19290 2.1 3.11203 2.4 0.11701 1.2 0.86 1137 22 1436 19 1911 22 60 NG1-seq3-c27 93940 164 66 0.89 36507 0.33284 2.5 5.28364 2.7 0.11513 1.0 0.93 1852 41 1866 23 1882 18 98 NG1-seq3-c28 85804 149 56 0.53 74278 0.33716 2.2 5.40707 2.4 0.11631 0.8 0.94 1873 36 1886 21 1900 15 99 NG1-seq3-c29 67063 321 72 1.36 12563 0.17734 2.5 2.03067 2.7 0.08305 1.1 0.92 1052 25 1126 19 1270 21 83 NG1-seq3-c30 102983 205 84 1.72 40312 0.30278 1.9 4.70895 2.1 0.11280 0.9 0.90 1705 28 1769 18 1845 17 92 NG1-seq3-c31 94327 287 77 1.03 19422 0.20823 5.1 3.20639 6.6 0.11168 4.1 0.78 1219 57 1459 52 1827 74 67 NG1-seq3-c32 109552 243 83 1.03 26492 0.26240 1.9 4.10820 2.5 0.11355 1.5 0.77 1502 25 1656 20 1857 28 81 NG1-seq3-c33 95653 395 78 0.45 7081 0.19261 1.9 3.01282 2.0 0.11345 0.7 0.94 1135 20 1411 15 1855 12 61 NG1-seq3-c34 71868 188 49 0.80 10018 0.22929 2.0 3.66713 2.3 0.11599 1.0 0.90 1331 24 1564 18 1895 17 70 NG1-seq3-c35 69652 362 69 0.58 7005 0.18471 2.1 2.25455 2.2 0.08852 0.8 0.93 1093 21 1198 16 1394 16 78 NG1-seq3-c36 142482 369 104 0.26 12499 0.27973 3.8 4.38877 4.0 0.11379 1.5 0.93 1590 53 1710 34 1861 27 85 NG1-seq3-c37 56496 128 53 1.83 3844 0.31358 1.9 4.79863 2.1 0.11098 0.7 0.94 1758 30 1785 17 1816 13 97 NG1-seq3-c38 56422 110 33 1.17 1538 0.22266 2.5 3.45923 3.1 0.11268 1.9 0.80 1296 29 1518 25 1843 34 70 NG1-seq3-c39 361888 259 127 1.18 87 0.30250 2.8 4.46132 5.4 0.10697 4.6 0.51 1704 41 1724 46 1748 85 97 NG1-seq3-c40 115484 253 74 1.25 15171 0.24016 1.9 3.75986 2.1 0.11355 0.7 0.94 1388 24 1584 17 1857 13 75 NG1-seq3-c41 35324 128 17 0.97 6229 0.11325 2.5 1.89192 2.9 0.12117 1.4 0.86 692 16 1078 19 1973 26 35 NG1-seq3-c42 116197 182 47 0.45 25103 0.23202 3.3 3.93707 3.5 0.12307 1.2 0.94 1345 41 1621 29 2001 22 67 NG1-seq3-c43 47839 65 23 0.78 17273 0.29626 2.6 4.57038 2.8 0.11189 1.0 0.93 1673 39 1744 24 1830 19 91 NG1-seq3-c44 57183 117 34 1.05 9434 0.25960 2.5 3.80091 2.7 0.10619 1.0 0.93 1488 33 1593 22 1735 17 86 NG1-seq3-c45 48159 82 25 2.11 7446 0.22351 2.4 3.54467 2.6 0.11502 1.2 0.89 1300 28 1537 21 1880 22 69 NG1-seq3-c46 55384 113 26 1.41 21538 0.17574 3.9 2.75787 4.2 0.11381 1.3 0.95 1044 38 1344 32 1861 24 56 NG1-seq3-c47 34228 36 17 1.50 29537 0.34290 1.8 5.51773 2.3 0.11671 1.5 0.77 1901 29 1903 20 1906 26 100 NG1-seq3-c48 82605 335 30 0.63 3538 0.07855 3.7 1.13197 3.9 0.10451 1.3 0.95 487 17 769 21 1706 23 29 NG1-seq3-c49 42071 90 19 0.66 17526 0.18794 2.6 2.77372 2.9 0.10704 1.3 0.90 1110 27 1348 22 1750 23 63 NG1-seq3-c50 58978 250 31 0.68 4443 0.11939 2.0 1.46865 2.4 0.08922 1.2 0.86 727 14 918 14 1409 23 52 NG1-seq3-c51 102094 101 43 1.07 15670 0.33757 1.9 5.29427 2.4 0.11375 1.4 0.80 1875 31 1868 21 1860 26 101 NG1-seq3-c52 261261 147 79 0.60 1112 0.47512 4.7 11.17175 4.8 0.17053 0.8 0.99 2506 99 2538 46 2563 14 98 NG1-seq3-c56 126483 207 35 0.47 7618 0.15969 2.0 2.54322 2.4 0.11550 1.3 0.85 955 18 1284 17 1888 23 51 NG1-seq3-c57 63245 95 29 1.20 9130 0.26701 2.4 4.13876 2.6 0.11242 1.0 0.92 1526 33 1662 21 1839 19 83 NG1-seq3-c58 -------------------NG1-seq3-c59 114558 121 35 1.03 10368 0.24880 1.7 3.83196 1.9 0.11171 0.7 0.92 1432 22 1599 15 1827 13 78 NG1-seq3-c60 30004 28 8 1.24 26663 0.22612 3.2 3.53341 3.8 0.11333 1.9 0.86 1314 38 1535 30 1854 35 71 NG1-seq4-d01 55360 182 51 0.84 19379 0.23790 1.9 2.89369 2.3 0.08822 1.3 0.82 1376 24 1380 18 1387 26 99 NG1-seq4-d02 62568 172 48 0.94 10560 0.25401 1.8 4.00867 2.1 0.11446 1.1 0.86 1459 24 1636 17 1871 19 78 NG1-seq4-d03 43735 199 45 1.49 4184 0.17775 1.8 2.78934 2.2 0.11381 1.1 0.85 1055 18 1353 16 1861 20 57 NG1-seq4-d04 7647 31 7 1.04 2732 0.19937 2.6 3.11799 3.7 0.11343 2.7 0.71 1172 28 1437 29 1855 48 63 NG1-seq4-d05 63222 126 53 1.94 2320 0.31705 4.5 4.83938 5.7 0.11070 3.5 0.78 1775 70 1792 49 1811 64 98 NG1-seq4-d06 14084 26 12 1.61 12490 0.33306 2.2 5.25330 3.3 0.11439 2.5 0.67 1853 36 1861 29 1870 44 99 NG1-seq4-d07 36733 68 29 1.22 5661 0.33279 1.9 5.23800 2.4 0.11416 1.5 0.79 1852 30 1859 21 1867 26 99 NG1-seq4-d08 89554 167 63 0.91 5558 0.31285 2.0 4.88692 2.3 0.11329 1.2 0.85 1755 30 1800 20 1853 22 95 NG1-seq4-d09 37694 141 27 0.67 6948 0.16802 5.4 2.65783 5.6 0.11473 1.6 0.96 1001 50 1317 42 1876 29 53 NG1-seq4-d10 64794 219 46 1.28 3197 0.16581 1.9 2.61477 2.1 0.11438 0.9 0.91 989 17 1305 15 1870 15 53 NG1-seq4-d11 78303 158 57 0.57 19378 0.32348 3.7 5.18763 3.9 0.11631 1.0 0.97 1807 59 1851 34 1900 18 95 NG1-seq4-d12 42428 77 29 0.60 18388 0.33088 2.2 5.31746 2.6 0.11655 1.3 0.86 1843 36 1872 22 1904 24 97 NG1-seq4-d13 124179 391 80 0.60 9136 0.18823 2.7 2.94146 2.8 0.11334 0.8 0.96 1112 27 1393 21 1854 14 60 NG1-seq4-d14 16857 27 13 1.16 3786 0.37933 1.6 5.97306 2.3 0.11420 1.6 0.71 2073 29 1972 20 1867 29 111 NG1-seq4-d15 38034 171 33 0.86 9678 0.17334 3.6 2.73793 3.8 0.11456 1.2 0.95 1030 34 1339 28 1873 22 55 NG1-seq4-d16 66094 186 45 0.49 8750 0.24301 1.8 3.79596 2.1 0.11329 1.0 0.88 1402 23 1592 17 1853 17 76 NG1-seq4-d17 88549 57 35 0.55 46442 0.53233 2.9 14.12664 3.1 0.19247 1.0 0.95 2751 66 2758 30 2763 16 100 NG1-seq4-d18 92107 209 79 0.74 33261 0.33015 2.5 5.27066 2.7 0.11578 1.1 0.91 1839 40 1864 23 1892 20 97 NG1-seq4-d19 14566 99 13 0.92 5934 0.12519 2.8 1.44820 3.3 0.08390 1.8 0.84 760 20 909 20 1290 34 59 NG1-seq4-d20 134112 246 90 0.69 65753 0.31835 2.2 5.02368 2.5 0.11445 1.3 0.87 1782 34 1823 22 1871 23 95 NG1-seq4-d21 147446 377 119 1.19 914 0.23967 3.3 3.56334 3.4 0.10783 0.8 0.97 1385 41 1541 27 1763 15 79 NG1-seq4-d22 160410 215 86 0.49 63196 0.36152 2.0 8.46951 2.4 0.16991 1.3 0.83 1989 34 2283 22 2557 22 78 NG1-seq4-d23 33802 60 26 1.01 12897 0.34531 1.8 5.52036 2.4 0.11595 1.6 0.76 1912 30 1904 21 1895 28 101 NG1-seq4-d24 12325 38 10 1.14 12412 0.21923 4.2 3.03270 4.9 0.10033 2.5 0.86 1278 49 1416 38 1630 47 78 NG1-seq4-d25 128575 256 97 0.88 5382 0.31221 2.1 4.82236 2.4 0.11202 1.1 0.89 1752 33 1789 20 1832 20 96 NG1-seq4-d26 146231 141 75 0.57 20881 0.47588 2.2 11.55161 2.4 0.17605 1.0 0.90 2509 45 2569 23 2616 17 96 NG1-seq4-d27 66010 115 48 0.85 57016 0.34703 1.7 5.58610 2.2 0.11675 1.3 0.80 1920 29 1914 19 1907 23 101 NG1-seq4-d28 116872 433 83 0.31 5749 U a Pb a Th c 206 Pb 206 Pb e 2 σ 207 Pb e 2 σ 207 Pb e 2 σ rho 206 Pb 2 σ 207 Pb 2 σ 207 Pb 2 σ Number (cps) (ppm) (ppm) U 204 Pb 238 U % 235 U % 206 Pb % 238 U (Ma) 235 U (Ma) 206 Pb (Ma) NG3-seq1-a01 59813 107 40 0.86 52731 0.32022 2.8 5.04319 3.0 0.11422 1.0 0.94 1791 44 1827 26 1868 19 NG3-seq1-a02 163214 314 103 0.55 145935 0.29890 2.0 4.65767 2.2 0.11302 0.9 0.92 1686 30 1760 18 1848 15 NG3-seq1-a03 34273 62 22 0.58 8782 0.32317 2.6 5.15889 3.1 0.11578 1.6 0.86 1805 42 1846 26 1892 28 NG3-seq1-a04 18214 34 15 1.45 3324 0.34320 2.7 5.50957 3.3 0.11643 1.8 0.83 1902 45 1902 28 1902 32 NG3-seq1-a05 25741 51 19 0.75 23801 0.31636 2.4 4.77039 3.2 0.10936 2.1 0.75 1772 37 1780 27 1789 38 NG3-seq1-a06 14570 74 17 1.31 3653 0.19946 2.2 2.20686 2.8 0.08025 1.6 0.81 1172 24 1183 19 1203 32 NG3-seq1-a07 46695 95 33 0.96 41599 0.29189 3.4 4.57015 3.5 0.11356 0.9 0.96 1651 49 1744 30 1857 17 NG3-seq1-a08 57413 145 46 1.49 20900 0.23942 3.4 3.87726 3.8 0.11745 1.6 0.91 1384 43 1609 31 1918 28 NG3-seq1-a09 21297 44 18 1.40 18835 0.31582 2.2 4.94222 2.7 0.11350 1.5 0.83 1769 34 1809 23 1856 27 NG3-seq1-a10 16766 32 13 1.10 10779 0.33233 2.7 5.21351 3.1 0.11378 1.5 0.88 1850 44 1855 27 1861 27 NG3-seq1-a11 57507 127 44 0.80 51068 0.30437 2.5 4.75670 2.8 0.11334 1.2 0.90 1713 38 1777 24 1854 22 NG3-seq1-a12 27963 144 40 2.19 11760 0.19839 2.3 2.21285 2.7 0.08090 1.3 0.87 1167 25 1185 19 1219 26 NG3-seq1-a13 63767 147 60 1.29 55919 0.31884 2.4 5.05905 2.7 0.11508 1.1 0.90 1784 38 1829 23 1881 21 NG3-seq1-a14 144215 399 108 0.73 3956 0.23836 2.9 3.67603 3.2 0.11185 1.4 0.89 1378 36 1566 26 1830 26 NG3-seq1-a15 18324 39 17 1.36 16127 0.32594 2.9 5.16908 3.8 0.11502 2.4 0.78 1819 46 1848 33 1880 43 NG3-seq1-a16 112460 257 89 0.52 99741 0.31939 2.4 5.01795 2.5 0.11395 0.9 0.94 1787 37 1822 21 1863 16 NG3-seq1-a17 10695 41 11 0.92 6412 0.23549 3.0 2.89659 3.6 0.08921 1.9 0.84 1363 37 1381 27 1409 37 NG3-seq1-a18 79929 186 74 1.09 57799 0.32118 2.7 5.04354 2.9 0.11389 1.0 0.94 1795 42 1827 25 1862 18 NG3-seq1-a19 31080 63 24 0.82 16806 0.33875 2.3 5.65113 2.7 0.12099 1.4 0.85 1881 38 1924 24 1971 25 NG3-seq1-a20 87376 206 76 0.71 78771 0.32489 2.6 5.01900 2.8 0.11204 1.0 0.94 1814 42 1823 24 1833 17 NG3-seq1-a21 21152 57 21 1.24 11528 0.32318 2.1 5.05968 2.4 0.11355 1.2 0.88 1805 33 1829 20 1857 21 NG3-seq1-a22 50566 127 56 1.54 34248 0.33121 2.3 5.19243 2.6 0.11370 1.2 0.88 1844 38 1851 23 1859 22 NG3-seq1-a23 69987 218 75 0.84 25629 0.29417 2.2 4.32457 2.6 0.10662 1.4 0.83 1662 32 1698 22 1742 26 NG3-seq1-a24 59802 158 69 1.78 11921 0.32341 2.4 5.25460 2.8 0.11784 1.4 0.86 1806 38 1862 24 1924 26 NG3-seq1-a25 27411 68 31 2.03 16032 0.31991 2.5 5.46642 2.9 0.12393 1.4 0.87 1789 39 1895 25 2014 25 NG3-seq1-a26 31474 77 31 0.95 10387 0.33292 3.0 5.27828 3.6 0.11499 2.0 0.83 1853 48 1865 31 1880 36 NG3-seq1-a27 140948 437 134 0.61 12272 0.27103 2.3 4.23026 2.8 0.11320 1.6 0.83 1546 32 1680 23 1851 28 NG3-seq1-a28 47966 119 42 0.85 24454 0.31300 3.3 5.39675 3.9 0.12505 2.0 0.86 1755 51 1884 34 2030 35 NG3-seq1-a33 46427 138 55 0.96 25197 0.33453 2.7 5.22467 3.1 0.11327 1.5 0.87 1860 44 1857 27 1853 27 NG3-seq1-a34 30767 202 48 0.76 8936 0.21011 2.6 2.41195 3.2 0.08326 1.8 0.82 1229 29 1246 23 1275 36 NG3-seq1-a35 24302 80 31 1.13 2745 0.31660 3.3 4.77061 4.0 0.10929 2.1 0.85 1773 52 1780 34 1788 38 NG3-seq1-a36 60717 185 73 0.95 39951 0.32828 2.6 5.24399 2.8 0.11586 1.1 0.92 1830 41 1860 24 1893 20 NG3-seq1-a37 35654 102 35 0.57 26366 0.31929 2.9 5.07515 3.3 0.11528 1.7 0.86 1786 45 1832 29 1884 31 NG3-seq1-a38 58130 168 51 0.39 22415 0.28266 2.2 4.55589 2.8 0.11690 1.8 0.77 1605 31 1741 24 1909 32 NG3-seq1-a39 58621 178 64 1.04 12665 0.31368 2.0 4.80043 2.3 0.11099 1.1 0.89 1759 31 1785 19 1816 19 NG3-seq1-a40 6583 39 11 2.07 7347 0.21441 2.4 2.48899 3.3 0.08419 2.3 0.73 1252 28 1269 24 1297 44 NG3-seq1-a41 109044 307 103 0.58 31591 0.30464 2.4 4.78634 2.7 0.11395 1.3 0.87 1714 36 1783 23 1863 24 NG3-seq1-a42 14151 84 21 1.08 11893 0.21142 2.2 2.35947 3.0 0.08094 2.0 0.74 1236 25 1230 21 1220 39 NG3-seq1-a43 81194 200 76 0.90 34046 0.31843 2.7 4.96645 3.0 0.11312 1.4 0.89 1782 42 1814 26 1850 25 NG3-seq1-a44 40548 235 55 1.03 2198 0.20899 2.7 2.33181 3.1 0.08092 1.5 0.88 1223 30 1222 22 1220 29 NG3-seq1-a45 11935 42 9 0.74 2629 0.20408 3.1 3.10895 3.8 0.11049 2.2 0.81 1197 34 1435 30 1807 40 NG3-seq1-a46 4605 10 6 3.13 1899 0.32647 3.1 5.12613 4.1 0.11388 2.8 0.74 1821 49 1840 36 1862 51 NG3-seq1-a47 23271 87 24 0.76 17269 0.23912 2.0 2.91478 2.9 0.08841 2.0 0.71 1382 25 1386 22 1391 38 NG3-seq1-a48 23545 50 21 1.28 13022 0.33542 2.9 5.25791 3.2 0.11369 1.4 0.89 1865 47 1862 28 1859 26 NG3-seq1-a49 43232 91 34 1.01 12182 0.31667 2.3 5.07253 2.6 0.11617 1.3 0.88 1773 36 1832 22 1898 23 NG3-seq1-a50 59322 119 39 0.39 29528 0.31596 2.3 4.95672 2.7 0.11378 1.5 0.85 1770 36 1812 23 1861 26 NG3-seq1-a51 43636 263 49 1.23 7653 0.14910 3.7 1.71144 4.2 0.08325 2.0 0.88 896 31 1013 27 1275 40 NG3-seq1-a52 27337 64 20 1.10 11494 0.25080 2.9 3.87478 3.5 0.11205 1.9 0.83 1443 37 1608 28 1833 35 NG3-seq1-a53 24586 59 23 1.67 21662 0.31488 2.4 4.97677 2.8 0.11463 1.5 0.84 1765 36 1815 24 1874 27 NG3-seq1-a54 67889 127 51 0.91 20072 0.33130 2.8 5.21320 3.0 0.11412 1.0 0.94 1845 45 1855 26 1866 18 NG3-seq1-a55 21345 92 23 1.33 13704 0.18464 2.9 2.10121 3.3 0.08254 1.7 0.85 1092 29 1149 23 1258 34 NG3-seq1-a56 42011 76 30 0.74 27450 0.33741 2.8 5.32697 3.2 0.11450 1.5 0.88 1874 46 1873 28 1872 27 NG3-seq1-a57 19410 85 19 0.99 22790 0.19223 2.4 2.22994 2.8 0.08413 1.5 0.84 1133 25 1190 20 1296 30 NG3-seq1-a58 9429 17 6 0.83 8325 0.32859 2.6 5.19045 3.2 0.11456 1.9 0.81 1832 42 1851 28 1873 35 NG3-seq1-a59 34765 66 25 0.99 27394 0.31935 2.5 5.09907 3.0 0.11580 1.6 0.84 1787 39 1836 25 1892 29 NG3-seq1-a60 60248 111 43 0.91 25646 0.32332 2.5 5.06598 2.7 0.11364 1.1 0.91 1806 39 1830 23 1858 20 NG3-seq2-b01 55645 109 47 1.34 18107 0.32446 2.4 5.11229 2.8 0.11428 1.4 0.86 1811 38 1838 24 1868 25 NG3-seq2-b02 207899 361 148 0.42 158231 0.39107 2.7 7.13790 2.9 0.13238 1.0 0.94 2128 50 2129 26 2130 18 NG3-seq2-b03 191052 679 140 0.77 2370 0.17800 2.5 2.72861 2.9 0.11118 1.5 0.86 1056 25 1336 22 1819 27 NG3-seq2-b04 54280 158 39 0.51 3602 0.23505 1.9 3.17793 4.6 0.09806 4.2 0.41 1361 23 1452 36 1588 78 NG3-seq2-b09 83898 181 63 0.46 55170 0.32017 2.2 4.99651 2.5 0.11318 1.1 0.89 1791 34 1819 21 1851 21 NG3-seq2-b10 63702 139 60 1.28 55768 0.34177 2.1 5.39061 2.5 0.11439 1.2 0.87 1895 35 1883 21 1870 22 NG3-seq2-b11 100566 716 107 0.80 2658 0.12877 2.2 1.55432 2.5 0.08754 1.1 0.89 781 16 952 16 1373 22 NG3-seq2-b12 79057 78 48 1.51 12618 0.40366 3.2 11.33359 3.8 0.20363 2.1 0.84 2186 60 2551 37 2856 34 NG3-seq2-b13 71651 157 57 0.57 33068 0.33069 2.2 5.40521 2.4 0.11855 0.9 0.92 1842 35 1886 20 1934 16 NG3-seq2-b14 48172 258 45 1.14 4762 0.16257 1.8 1.96607 2.0 0.08771 0.9 0.90 971 17 1104 14 1376 17 NG3-seq2-b15 136960 300 128 1.44 12423 0.32889 2.1 5.27440 2.5 0.11631 1.3 0.85 1833 34 1865 22 1900 24 NG3-seq2-b16 43897 95 39 1.05 37864 0.33353 2.5 5.37223 2.7 0.11682 1.0 0.92 1855 41 1880 24 1908 19 NG3-seq2-b17 66124 174 47 0.56 24698 0.24731 2.6 3.78186 3.0 0.11091 1.5 0.86 1425 33 1589 24 1814 27 NG3-seq2-b18 55372 125 55 1.61 48640 0.33145 2.0 5.24329 2.4 0.11473 1.2 0.85 1845 32 1860 20 1876 22 NG3-seq2-b19 60973 133 55 1.35 21064 0.32065 2.3 5.09494 2.6 0.11524 1.1 0.90 1793 36 1835 22 1884 21 NG3-seq2-b20 58274 139 52 0.96 14414 0.33609 2.2 5.46393 2.4 0.11791 1.1 0.89 1868 35 1895 21 1925 20 NG3-seq2-b21 29652 170 47 1.94 11450 0.19187 3.7 2.26354 5.1 0.08556 3.5 0.73 1132 39 1201 37 1328 67 NG3-seq2-b22 79819 186 60 0.14 69303 0.32425 2.4 5.13546 2.7 0.11487 1.2 0.89 1810 39 1842 24 1878 22 NG3-seq2-b23 109538 351 77 1.27 3832 0.16589 2.9 2.65044 3.7 0.11588 2.3 0.79 989 27 1315 28 1894 41 NG3-seq2-b24 114051 340 122 0.51 8028 0.34072 2.9 5.51101 3.2 0.11731 1.5 0.89 1890 47 1902 28 1916 27 NG3-seq2-b25 66167 459 95 1.30 7621 0.15614 3.3 1.74688 3.6 0.08114 1.3 0.93 935 29 1026 23 1225 26 NG3-seq2-b26 162446 563 163 0.83 7103 0.26434 2.3 4.07002 2.6 0.11167 1.0 0.92 1512 32 1648 21 1827 19 NG3-seq2-b27 195387 1072 161 0.46 1484 0.13814 2.5 2.07652 3.1 0.10902 1.8 0.81 834 20 1141 22 1783 33 NG3-seq2-b28 9411 21 8 0.88 3782 0.34427 2.5 5.55629 3.1 0.11705 1.9 0.78 1907 41 1909 27 1912 35 NG3-seq2-b29 76211 197 71 0.76 31104 0.31764 2.1 5.07105 2.5 0.11579 1.3 0.86 1778 33 1831 21 1892 23 NG3-seq2-b30 50237 125 51 1.39 28698 0.31784 2.4 5.04716 2.9 0.11517 1.5 0.85 1779 38 1827 24 1883 27 NG3-seq2-b31 9092 46 11 0.96 3817 0.21156 2.2 2.40113 3.0 0.08231 2.0 0.75 1237 25 1243 22 1253 39 NG3-seq2-b32 83492 222 86 1.18 73989 0.32292 2.3 5.06445 2.8 0.11374 1.6 0.81 1804 36 1830 24 1860 29 NG3-seq2-b33 127541 331 114 0.43 108940 0.31879 2.1 5.18966 2.4 0.11807 1.3 0.85 1784 32 1851 21 1927 23 NG3-seq2-b34 57393 169 60 0.73 18931 0.32099 2.3 5.05250 2.8 0.11416 1.6 0.81 1795 35 1828 24 1867 30 NG3-seq2-b35 160734 764 157 0.88 2629 0.19048 2.9 2.83249 3.4 0.10785 1.9 0.84 1124 30 1364 26 1763 34 NG3-seq2-b36 34676 97 36 1.30 29723 0.29920 3.2 4.85321 3.6 0.11764 1.7 0.88 1687 47 1794 31 1921 31 NG3-seq2-b37 121567 336 107 0.58 17142 0.30483 1.9 4.69990 2.1 0.11182 0.9 0.91 1715 28 1767 17 1829 16 NG3-seq2-b38 37790 98 34 1.25 5380 0.26902 3.0 4.11383 3.5 0.11091 1.8 0.85 1536 41 1657 29 1814 33 NG3-seq2-b39 75168 170 61 1.04 15754 0.29132 2.4 4.62689 2.7 0.11519 1.3 0.88 1648 35 1754 23 1883 24 NG3-seq2-b40 7624 15 7 1.51 1478 0.33582 2.5 5.41767 3.1 0.11701 1.8 0.82 1867 41 1888 27 1911 32 0.19114 4.2 3.00082 4.3 0.11387 1.0 0.97 1128 43 1408 33 1862 18 Tab. 4: 207 Pb NG3-seq1-a29 51213 138 58 1.31 17043 0.32682 2.3 5.13832 3.0 0.11403 1.9 0.77 1823 37 1842 26 1865 35 NG3-seq2-b05 52692 109 43 1.13 19312 0.31839 2.3 5.05487 2.6 0.11515 1.3 0.87 1782 36 1829 22 1882 23 NG3-seq2-b41 39643 87 28 0.54 13643 0.29722 2.5 4.60651 2.7 0.11241 1.0 0.92 1678 37 1750 23 1839 19
		NG1-seq1-a29 64759 NG1-seq2-b05 270981 126 164 NG1-seq2-b41 27452 26 NG1-seq3-c17 23123 93 NG1-seq3-c53 81605 121 NG3-seq1-a30 134743 744 NG3-seq2-b06 40955 87 NG3-seq2-b42 39710 81	58 79 12 27 29 162 0.52 3907 1.20 12527 0.27252 2.7 4.42250 3.8 0.11770 2.6 0.72 1554 38 1717 32 1922 47 0.50 23697 0.54250 2.3 14.86811 2.5 0.19877 1.0 0.92 2794 52 2807 24 2816 16 0.46 21031 0.40429 2.1 7.36855 2.6 0.13219 1.4 0.84 2189 40 2157 23 2127 24 1.63 21180 0.20425 2.3 2.31147 2.9 0.08208 1.7 0.79 1198 25 1216 20 1247 34 0.89 9285 0.21666 2.1 3.42218 2.4 0.11456 1.2 0.86 1264 24 1510 19 1873 22 0.19313 2.2 3.07075 2.5 0.11532 1.2 0.88 1138 23 1425 20 1885 21 32 0.78 36058 0.32286 2.9 5.09788 3.3 0.11452 1.5 0.89 1804 46 1836 28 1872 27 31 1.18 34604 0.30842 2.2 4.85743 2.7 0.11422 1.6 0.81 1733 33 1795 23 1868 28	81 99 103 96 67
		NG1-seq1-a30 67137 NG1-seq2-b06 83500 NG1-seq2-b42 21953 NG1-seq3-c18 283433 626 170 108 69 NG1-seq3-c54 55271 70 NG3-seq1-a31 61942 175 NG3-seq2-b07 41126 233 NG3-seq2-b43 38638 74	68 46 15 150 0.24 23514 0.23617 2.4 3.89750 5.0 0.11969 4.4 0.48 1367 30 1613 41 1952 78 1.32 27487 0.32295 1.8 5.13677 2.1 0.11536 1.0 0.87 1804 28 1842 18 1885 18 0.96 73692 0.34158 2.5 5.39457 2.9 0.11454 1.5 0.85 1894 41 1884 25 1873 28 0.64 2956 0.20645 4.6 2.56225 5.1 0.09001 2.2 0.90 1210 51 1290 38 1426 41 26 0.88 15531 0.31893 3.0 4.81171 3.3 0.10942 1.5 0.90 1785 47 1787 28 1790 27 71 1.13 22938 0.33401 2.5 5.31428 2.8 0.11540 1.3 0.89 1858 41 1871 25 1886 24 40 0.88 4159 0.16043 2.7 1.89934 3.0 0.08586 1.4 0.89 959 24 1081 20 1335 27 30 0.99 13732 0.33496 2.2 5.17457 2.7 0.11204 1.6 0.82 1862 36 1848 23 1833 29	96 101 85 70 100
		NG1-seq1-a31 34446 NG1-seq2-b07 94647 NG1-seq2-b43 102453 131 161 125 NG1-seq3-c19 49921 153 NG1-seq3-c55 46058 73 NG3-seq1-a32 46339 302 NG3-seq2-b08 51478 109 NG3-seq2-b44 44440 79	34 54 52 37 17 72 43 32	0.42 40357 0.20090 2.3 2.39795 2.9 0.08657 1.7 0.81 1180 25 1242 21 1351 32 1.01 41968 0.34244 2.4 5.49081 2.7 0.11629 1.3 0.88 1898 40 1899 24 1900 24 0.80 77523 0.33448 2.7 5.24806 2.9 0.11380 1.2 0.92 1860 43 1860 25 1861 21 0.97 1768 0.21650 2.6 3.58834 3.3 0.12021 2.0 0.79 1263 29 1547 26 1959 36 0.55 10306 0.22676 1.9 3.17304 2.4 0.10149 1.5 0.78 1318 23 1451 19 1651 28 0.89 48939 0.20650 2.3 2.36453 2.7 0.08305 1.4 0.85 1210 26 1232 20 1270 28 1.29 11310 0.29813 1.8 4.66709 2.4 0.11354 1.6 0.76 1682 27 1761 20 1857 28 1.33 23294 0.32706 1.8 5.16654 2.2 0.11457 1.1 0.86 1824 29 1847 19 1873 20	87 100 100 64 80
		0.018																				2
		0.016
		0.014
	Probability	0.006 0.008 0.010 0.012																				1	Frequency
		0.004
		0.002
		0.000																				0
		1000	1100	1200	1300	1400	1500	1600	1700	1800	1900	2000	2100	2200	2300	2400	2500	2600	2700	2800	2900	3000
										Age (Ma)

[START_REF] Stacey | Approximation of terrestrial lead isotope evolution by a twostage model[END_REF] model Pb composition.207 Pb/ 235 U calculated using 207 Pb/ 206 Pb/( 238 U/ 206 Pb × 1/137.88). Errors are propagated by quadratic addition of within-run errors (2SE) and the reproducibility of GJ-1 (2SD). d Rho is the error correlation defined as err 206 Pb/ 238 U/err 207 Pb/ 235 U.

Tab. 3: U-Pb-Th data of zircon from sample NG2, n = 95 of 143 measured zircon grains (90-110 % conc.)