Augustin Y Koffi
email: yaoaugustinkoffi@yahoo.fr

Nicolas Thébaud

Alain N Kouamelan

Lenka Baratoux

Olivier Bruguier

Olivier Vanderhaeghe

Pavel Pitra

Anthony I S Kemp

Noreen Evans

Archean to Paleoproterozoic crustal evolution in the Sassandra-Cavally domain (Côte d'Ivoire, West Africa): Insights from Hf and U-Pb zircon analyses

Keywords: zircon geochronology, U-Pb and Lu-Hf isotopes, juvenile crustal growth, crustal growth and reworking, Archean, West African Craton, Côte d'Ivoire

published or not. The documents may come   L'archive ouverte pluridisciplinaire

 [START_REF] Grenholm | The Birimian event in the Baoulé Mossi domain (West African Craton): regional and global context[END_REF]. The position of the present-day margins of the craton are constrained by geophysical data [START_REF] Jessell | The geophysical signatures of the West African Craton[END_REF], (B) Simplified geological map of the Leo-Man Shield (modified after Agyei et al., 2009;[START_REF] Baratoux | Juvenile Paleoproterozoic crust evolution during the Eburnean orogeny (∼2.2-2.0Ga), western Burkina Faso[END_REF][START_REF] Egal | Late Eburnean granitization and tectonics along the western and northwestern margin of the Archean Kénéma-Man domain (Guinea, West African Craton)[END_REF][START_REF] Grenholm | The Birimian event in the Baoulé Mossi domain (West African Craton): regional and global context[END_REF][START_REF] Thiéblemont | An updated geological map of Africa at 1/10 000 000 scale[END_REF]. Bog sz: Bougouni shear zone; Ban: Banifing shear zone.

GEOLOGICAL SETTING

The Leo-Man Shield consists of the Kenema-Man domain in the west, made of Archean terranes, and the Baoulé-Mossi domain in the east, made of Paleoproterozoic formations designated as the Birimian [START_REF] Armstrong | Données géochronologiques nouvelles sur l'Archéen de l'Amsaga (Dorsale Réguibat, Mauritanie)[END_REF][START_REF] Bessoles | Géeologie de l'Afrique. Le craton Ouest Africain[END_REF][START_REF] Milési | Minéralisations aurifères de l'Afrique de l'ouest leurs relations avec l'évolution lithostructurale au Proterozoique inférieur[END_REF][START_REF] Thiéblemont | Archean evolution of the Leo Rise and its Eburnean reworking[END_REF]. The Kenema-Man domain covers Liberia, Sierra Leone and part of Guinea as well as Côte d'Ivoire and is dominated by plutons of tonalite-trondhjemitegranodiorite (TTG), gneissic domains and meta volcano-sedimentary belts composed of metasedimentary and metavolcanic rocks that underwent amphibolite to granulite facies matamorphism [START_REF] Barth | Re Os and U Pb geochronological constraints on the eclogite-tonalite connection in the Archean Man Shield, West Africa[END_REF][START_REF] Camil | Un exemple de métamorphisme prograde de la base du faciès des amphibolites au faciès des granulites dans la région de Man (Ouest de la Côte d'Ivoire)[END_REF][START_REF] Camil | Pétrographie, chronologie des ensembles granulitiques archéens et formations associées de la région de Man (Côte d'Ivoire) Implication pour l'histoire géologique du Craton Ouest-Africain[END_REF][START_REF] Gouedji | The Samapleu mafic-ultramafic intrusion and its Ni-Cu-PGE mineralization: an Eburnean (2.09 Ga) feeder dyke to the Yacouba layered complex (Man Archean craton, western Ivory Coast)[END_REF][START_REF] Pitra | Palaeoproterozoic high-pressure granulite overprint of the Archean continental crust: evidence for homogeneous crustal thickening (Man Rise, Ivory Coast)[END_REF].

The metavolcanic-sedimentary belts are bound by shear zones and alternate with TTG-type granitoids, granites and gneissic domains. The Kenema-Man domain gneisses display U-Pb zircon ages ranging from ca. 3600 to 2600 Ma [START_REF] Gouedji | The Samapleu mafic-ultramafic intrusion and its Ni-Cu-PGE mineralization: an Eburnean (2.09 Ga) feeder dyke to the Yacouba layered complex (Man Archean craton, western Ivory Coast)[END_REF][START_REF] Milési | Early Proterozoic ore deposits and tectonics of the Birimian orogenic belt, West Africa[END_REF][START_REF] Rollinson | Archaean crustal evolution in West Africa: A new synthesis of the Archaean geology in Sierra Leone, Liberia, Guinea and Ivory Coast[END_REF][START_REF] Rollinson | The geochemical evolution of Archaean felsic gneisses in the West African Craton in Sierra Leone[END_REF][START_REF] Thiéblemont | A 3.5 Ga granite-gneiss basement in Guinea: further evidence for early archean accretion within the West African Craton[END_REF][START_REF] Thiéblemont | Archean evolution of the Leo Rise and its Eburnean reworking[END_REF]) that were initially interpreted to be the result of two orogenic cycles, the Leonian (~ 3400-3000 Ma) and the Liberian (~ 2900-2700 Ma) [START_REF] Barth | Re Os and U Pb geochronological constraints on the eclogite-tonalite connection in the Archean Man Shield, West Africa[END_REF][START_REF] Egal | Late Eburnean granitization and tectonics along the western and northwestern margin of the Archean Kénéma-Man domain (Guinea, West African Craton)[END_REF][START_REF] Koffi | Reevaluation of Leonian and Liberian events in the geodynamical evolution of the Man-Leo Shield (West African Craton)[END_REF][START_REF] Milési | Minéralisations aurifères de l'Afrique de l'ouest leurs relations avec l'évolution lithostructurale au Proterozoique inférieur[END_REF][START_REF] Thiéblemont | Archean evolution of the Leo Rise and its Eburnean reworking[END_REF]. Recent work conducted in the Kenema-Man Domain by [START_REF] Rollinson | Archaean crustal evolution in West Africa: A new synthesis of the Archaean geology in Sierra Leone, Liberia, Guinea and Ivory Coast[END_REF] has further documented zircon age clusters at ca. 3500 Ma, ca. 3260-3050 Ma and ca. 2960-2850 Ma, interpreted as several distinct magmatic events. The older ages are also found in xenocrystic zircon cores in younger rocks suggesting a partial reworking of the older domains.

The Baoulé-Mossi domain records the formation of a large volume of continental crust between ca. 2300 and 2070 Ma and covers Burkina Faso, Ghana and parts of Côte d'Ivoire, Mali, Guinea, Niger and Togo [START_REF] Abouchami | A major 2.1 Ga event of mafic magmatism in west Africa: An Early stage of crustal accretion[END_REF][START_REF] Boher | Crustal growth in West Africa at 2[END_REF][START_REF] Egal | Late Eburnean granitization and tectonics along the western and northwestern margin of the Archean Kénéma-Man domain (Guinea, West African Craton)[END_REF]. This area consists of deformed and metamorphosed volcanic (tholeiitic and calc-alkaline), volcanosedimentary and sedimentary rock, all intruded by different generations of granitic rocks showing overall Paleoproterozoic juvenile Nd as well as Hf isotopic signatures [START_REF] Abouchami | A major 2.1 Ga event of mafic magmatism in west Africa: An Early stage of crustal accretion[END_REF][START_REF] Salah | Evolution d'un arc insulaire océanique birimien précoce au Liptako nigérien (Sirba): géologie, géochronologie et géochimie[END_REF][START_REF] Baratoux | Juvenile Paleoproterozoic crust evolution during the Eburnean orogeny (∼2.2-2.0Ga), western Burkina Faso[END_REF][START_REF] Béziat | A Paleoproterozoic ultramafic-mafic assemblage and associated volcanic rocks of the Boromo greenstone belt: fractionates originating from island-arc volcanic activity in the West African craton[END_REF][START_REF] Doumbia | Petrogenesis of juvenile-type Birimian (Paleoproterozoic) granitoids in Central Côte-d'Ivoire, West Africa: geochemistry and geochronology[END_REF][START_REF] Feybesse | The paleoproterozoic Ghanaian province: Geodynamic model and ore controls, including regional stress modeling[END_REF][START_REF] Ganne | Thermo-mechanical modeling of lower crust exhumation-Constraints from the metamorphic record of the Palaeoproterozoic Eburnean orogeny, West African Craton[END_REF][START_REF] Gasquet | Structure, Sr-Nd isotope geochemistry and zircon U-Pb geochronology of the granitoids of the Dabakala area (Côte d'Ivoire): evidence for a 2.3 Ga crustal growth event in the Palaeoproterozoic of West Africa?[END_REF][START_REF] Hirdes | Two generations of Birimian (Paleoproterozoic) volcanic belts in northeastern Côte d'Ivoire (West Africa): consequences for the 'Birimian controversy[END_REF][START_REF] Liégeois | Short-lived Eburnian orogeny in southern Mali. Geology, tectonics, U-Pb and Rb-Sr geochronology[END_REF][START_REF] Parra-Avila | Crustal evolution of the Paleoproterozoic Birimian terranes of the Baoulé-Mossi domain, southern West African Craton: U-Pb and Hf-isotope studies of detrital zircons[END_REF][START_REF] Pouclet | Geodynamic setting of the Birimian volcanism in central Ivory Coast (western Africa) and its place in the Palaeoproterozoic evolution of the Man Shield[END_REF][START_REF] Tapsoba | Chemical and Sr-Nd isotopic compositions and zircon U-Pb ages of the Birimian granitoids from NE Burkina Faso, West African Craton: Implications on the geodynamic setting and crustal evolution[END_REF][START_REF] Vidal | Evolution of a Paleoproterozoic "weak type" orogeny in the West African Craton (Ivory Coast)[END_REF]. Deformation and metamorphism of these rocks has been attributed to the Eoeburnean (~2250 to 2150 Ma) and Eburnean orogenies (~2140 to 2100 Ma) [START_REF] Hirdes | Two generations of Birimian (Paleoproterozoic) volcanic belts in northeastern Côte d'Ivoire (West Africa): consequences for the 'Birimian controversy[END_REF][START_REF] Liégeois | Short-lived Eburnian orogeny in southern Mali. Geology, tectonics, U-Pb and Rb-Sr geochronology[END_REF][START_REF] Macfarlane | The tectono-magmatic framework to gold mineralisation in the Sadiola-Yatela gold camp and implications for the paleotectonic setting of the Kédougou-Kénieba inlier, West Africa[END_REF][START_REF] Tshibubudze | The relative and absolute chronology of strato-tectonic events in the Gorom-Gorom granitoid terrane and Oudalan-Gorouol belt, northeast Burkina Faso[END_REF][START_REF] Wane | The onset of the Eburnean collision with the Kenema-Man craton evidenced by plutonic and volcanosedimentary rock record of the Masssigui region, southern Mali[END_REF].

Metamorphism is typically characterized by regional greenschist facies conditions (Hirdes et al., 1992;[START_REF] Kříbek | Graphitization of organic matter and fluid-deposited graphite in Palaeoproterozoic (Birimian) black shales of the Kaya-Goren greenstone belt (Burkina Faso, West Africa)[END_REF][START_REF] Taylor | Early Proterozoic crustal evolution in the birimian of Ghana: constraints from geochronology and isotope geochemistry[END_REF], but locally reaches amphibolite facies or even granulite facies metamorphism [START_REF] Block | Petrological and geochronological constraints on lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton[END_REF][START_REF] Ganne | Thermo-mechanical modeling of lower crust exhumation-Constraints from the metamorphic record of the Palaeoproterozoic Eburnean orogeny, West African Craton[END_REF][START_REF] John | The metamorphic evolution of the paleoproterozoic (Birimian) volcanic Ashanti belt (Ghana, West Africa)[END_REF][START_REF] Pons | Mechanisms of pluton emplacement and structural evolution of a 2.1 Ga juvenile continental crust: the Birimian of southwestern Niger[END_REF][START_REF] Soumaila | Le metamorphisme des formations de la ceinture de roches vertes birrimienne (paleoproterozoique) de Diagorou-Darbani (Liptako, Niger, Afrique de l'Ouest)[END_REF].

Fig. 2.

Litho-structural map of the SW of Côte d'Ivoire, modified after [START_REF] Papon | Géologie et minéralisations du Sud-Ouest de la Côte d'Ivoire : Synthèse des travaux de l'opération SASCA[END_REF][START_REF] Pitra | Palaeoproterozoic high-pressure granulite overprint of the Archean continental crust: evidence for homogeneous crustal thickening (Man Rise, Ivory Coast)[END_REF][START_REF] Tagini | Esquisse structurale de la Côte d'Ivoire. Essai de géotectonique régionale[END_REF]WAXI report, AMIRA Global, 2018). Purple stars show the location of the studied rocks of the SASCA domain.

GEOLOGY OF THE SASSANDRA-CAVALLY DOMAIN

The SASCA domain located at the border between Côte d'Ivoire and Liberia consists of Archean metamorphic and granitic basement rocks overlain by Birimian pelitic formations interlayered with acid and basic tuffs [START_REF] Papon | Géologie et minéralisations du Sud-Ouest de la Côte d'Ivoire : Synthèse des travaux de l'opération SASCA[END_REF]. Sm-Nd whole rock model ages of ca. 3450

Ma have been obtained on migmatitic gneiss of San Pedro, and ca. 2400 Ma on metapelitic schists at Kounoukou. The presence of Archean crustal relics has been confirmed by a U-Pb zircon age of 3207 ± 7 Ma [START_REF] Kouamelan | The oldest rock of Ivory Coast[END_REF]. Based on the study of the coastal section between Grand-Béréby and Sassandra by [START_REF] Koffi | Evolution tectono-métamorphique du Craton Ouest Africain : Exemple du secteur de Grand-Béréby a Sassandra (Sud-Ouest de la Côte d'Ivoire)[END_REF], polyphase deformation was documented in the SASCA domain. The first deformation phase is characterized by a NW-SEoriented subvertical penetrative metamorphic foliation S1 with occasional synfolial rootless folds. The S1 is affected by open F2 folds with shallow NNE-plunging axes and by dominantly sinistral ductile NNE-SSW trending shear-zones. At San Pedro, the shear zones locally crosscut the fold limbs. The presence of leucosome and pegmatite veins concordant to the S1 and S2 foliation planes, as well as in axial planes of F2 folds or in shear zones, indicates that deformation occurred in the presence of melt, which in turn promoted melt segregation (Fig. 3). The migmatitic gneiss comprises veins of granite discordant to S2 but in a structural position similar to discordant leucosome suggesting an origin by segregation of partial melts from the migmatitic gneiss. The L2 mineral lineation plunges between 80° and 30° to the NNE. Open F3 folds with W-plunging axes and a penetrative subvertical E-W axial planar schistosity S3 affect the S1 and S2 foliations. In Monogaga, the F3 folds with E-W axial planes overprint the F2, leading to hook-shape fold interference paterns. In the San Pedro area, discrete E-W-striking dextral shear-zones S4 are localized along the contact between a potassic granite and the migmatitic gneisses (Fig. 3c, [START_REF] Koffi | Evolution tectono-métamorphique du Craton Ouest Africain : Exemple du secteur de Grand-Béréby a Sassandra (Sud-Ouest de la Côte d'Ivoire)[END_REF].

ANALYTICAL METHODS

Thirteen samples were collected for this study in the Sassandra-Cavally domain at San Pedro along a coastal transect, which covers the zone of transition (Sassandra shear zone) between the Archean and Paleoproterozoic metamorphic and magmatic units: (migmatitic gneisses and potassic granite: 5 and 1 samples, respectively), Monogaga (migmatitic gneisses, 2 samples), Grand-Béréby (garnet-cordierite-sillimanite migmatitic gneiss, 4 samples), and Kounoukou (garnet-staurolite-bearing micaschist, 1 sample). Only a representative subset of these samples was analysed for geochronology (SP3B, SP11, MON4, GDB8, KOU7, CIS62) (Fig. 2).

Geochemical characterisation

Whole rock major and trace elements were analysed in 13 samples (SP3B, Bal1-2, Bal2-4, Por1, SP1B, SP11, MON4, GDB3, GDB4, GDB5, GDB8, KOU7 and CIS62) at Actlabs in Ancaster (Canada) (Table 1). Samples were digested by lithium metaborate and tetraborate fusion. Major and trace elements analyses were achieved by ICP-OES and ICP-MS, respectively (Table 1).

Fe is measured as total Fe2O3. In the multi-element diagrams, the abundances were normalized with respect to primitive-mantle and chondrites according to the values established by [START_REF] Mcdonough | Potassium, rubidium, and cesium in the Earth and Moon and the evolution of the mantle of the Earth[END_REF] and [START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF], respectively.

Radiogenic isotopic geochemistry

Six of the samples characterised by geochemistry (SP3B, GDB8, KOU7, CIS62, SP11 and MON4) were further analysed for zircon U-Pb and Lu-Hf by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICPMS). The description of the analytical methods applied is presented in supplementary materials and the acquired data are provided in Table 2. (d) major element in wt% and trace elements in ppm.

RESULTS

Petrographic characteristics -Migmatitic gneisses of San Pedro

Macroscopically, the rocks are banded grey migmatitic gneisses. The sample SP3B comprises quartz (40%), plagioclase (35%), greenish biotite (20%) and garnet (3%). Monazite, ilmenite, magnetite and zircon are the main accessory minerals. The foliation is marked by alternating quartzo-feldspathic and biotite-rich layers, several mm up to 1 cm thick. Locally, significantly coarser-grained quartzo-feldspathic leucosomes, up to 10 cm thick, are present with a spacing of 20-50 cm. Leucosomes are forming a continuous network from veins concordant with the S1 foliation to veins parallel to the axial planar S2 foliation but may also be localised in necks of foliation boudins (Figs. 3a, b, c and4a). E-W trending subvertical shear bands S4 cross-cut the NE-trending foliation S2. Greenish biotite is aligned parallel to the S2 foliation but also commonly crystallizes around garnet. Monazite tyically forms crystal aggregates in the leucosome, aligned parallel to the foliation S2 and locally occurs as inclusions in garnet.

Numerous grains of zircon are included in biotite, feldspar and garnet.

-Migmatitic gneisses of Monogaga

Macroscopically, the sample SP11 is a grey migmatitic gneiss. This rock comprises medium to coarse-grained plagioclase (40%), quartz (35%), greenish biotite (20%), greenish hornblende (2%) and locally minor garnet (Fig. 4b). Zircon and ilmenite are the main accessory minerals.

The syn-migmatitic foliation S2 is marked by alternating quartzo-feldspathic and biotite-rich layers including rare greenish hornblende, representing leucosomes and mesosomes, several mm up to 1 cm thick. Biotite flakes show preferred orientation parallel to S2.

Sample MON4, collected at ca. 500 meters to the east of SP11, is also a grey, medium to coarse grained (up to 5 mm) migmatitic gneiss. It consists of hornblende (40%), plagioclase (30%), quartz (25%) and K-feldspar (3%). Epidote, zircon, ilmenite and magnetite are the main accessory minerals. The foliation S2 is marked by hornblende-rich and quartz-feldspar-rich layers with thicknesses ranging from several mm to up to 1 cm (Fig. 4c).

-Garnet-cordierite-sillimanite migmatitic gneiss of Grand-Béréby

Macroscopically, the gneiss of Grand-Béréby (GDB8) displays a prominent migmatitic texture with coarse-grained quartzo-feldspathic leucosome layers (1-10 cm thick), rimmed by thin layers of biotite-rich melanosome, and alternating with layers of mesosome. The mineralogy of the mesosome consists of biotite (35%), quartz (30%), plagioclase (25%), sillimanite (5%), garnet (3%) and cordierite (2%). Zircon, ilmenite, magnetite and hematite are the main accessory minerals. Biotite and sillimanite show preferred orientation along the foliation S2 which wraps around anhedral porphyroblasts of garnet (up to 2.5 mm). Garnet is commonly surrounded by cordierite and locally replaced by symplectitic intergrowths of biotite and quartz.

(Fig. 4d). The mineral assemblages of the mesosomes suggests a sedimentary, pelitic protolith.

-Garnet-staurolite-bearing micaschist of Kounoukou

A macroscopically dark-colored micaschist from Kounoukou (KOU7) consists of quartz (35%), biotite (35%), plagioclase (15%), garnet (5%) and staurolite (5%). Zircon, ilmenite and tourmaline are the main accessory minerals. Garnet and staurolite form porphyroblasts (up to 3 mm) in a matrix dominated by quartz and plagioclase. Biotite, commonly altered to chlorite, marks the foliation S3. Subhedral garnet contains abundant inclusions of quartz. Poikiloblastic staurolite contains abundant quartz inclusions. (Fig. 4e). The mineral assemblage with the preserved sedimentary bedding suggests a sedimentary, pelitic protolith.

-Potassic granite of San Pedro

The potassic granite (CIS62) intrudes the migmatitic grey gneiss of San Pedro. The mineralogy consists of quartz (35%), plagioclase (25%), K-feldspar (25%), biotite (10%) and muscovite (5%). Plagioclase occurs both as phenocrysts and in the groundmass. K-feldspar is microcline, commonly displays a cloudy appearance and is locally overgrown by muscovite (Fig. 4f).

Geochemical characteristics -Migmatitic gneisses of San Pedro

The migmatitic gneisses of San Pedro (orange squares, Fig. 5a) are characterized by relatively high SiO2 (64.9-71.2 wt%), Al2O3 (13.8-16.3 wt%) and Na2O (3.8-4.9 wt%). These migmatitic gneisses are also characterized by low MgO (1.2-2.3 wt%), TiO2 (0.3-0.6 wt%), and Fe2O3

(3.5-5.6 wt%) compared to other samples, while CaO (1.9-4.1 wt%), K2O (1.4-2.1 wt%) and

-Migmatitic gneisses of Monogaga

Sample SP11 (light purple ellipse, Fig. 5a) shows higher SiO2 (66.7 wt%) than migmatitic gneiss of Monogaga MON4 (light blue diamond, SiO2 = 55.9 wt%). Values of Al2O3, Na2O and TiO2 of SP11 (15.3, 4.1 and 0.5 wt%) are essentially the same as MON4 (14.4, 3.5 and 0.5 wt%). In contrast, Fe2O3, MgO and CaO of MON4 (10.4, 5.3 and 8.6 wt%) are higher than those of SP11 (4.7, 2.3 and 3.1 wt%) while K2O and P2O5 are lower in MON4 (0.8 and 0.1 wt%) than in SP11 (2.2 and 0.2 wt%) (Fig. 5a). MON4 is metaluminous (A/CNK = 0. anomalies and negative K, Nb and Ti as well as a slight negative Ta anomaly in SP11 (Fig. 6).

-Garnet-cordierite-sillimanite migmatitic gneiss of Grand-Béréby

The garnet-cordierite-sillimanite migmatitic gneisses of Grand-Béréby (yellow stars, Fig. 5a) display intermediate to high SiO2 (56.4-65.0 wt%), relatively high Al2O3 (15.2-19.6 wt%), Fe2O3 (8.4-10.4 wt%), TiO2 (0.7-1.0 wt%) and relatively low MgO (2.2-3.9 wt%), Na2O (2.0-3.2 wt%), CaO (1.3-2.6 wt%), K2O (2.0-2.2 wt%), P2O5 (0.05-0.2 wt%). They are strongly peraluminous (A/CNK = 1.3-2.3 and A/NK = 2.0-3.3) (Fig. 5b). Sr/Y varies between 7.7 and 13, K2O/Na2O is comprised between 0.7 and 1.1 (Fig. 5c). The source of the garnet-cordieritesillimanite migmatitic gneiss of Grand-Béréby defines a trend to the metasediments field (Fig. fall in the field of sedimentary source and high-K mafic rocks source, due to their higher K2O /Na2O ratio (Fig. 5e).

-Garnet-staurolite-bearing micaschist of Kounoukou Garnet-staurolite-bearing micaschist of Kounoukou (light green polygone, Fig. 5a) shows relatively high SiO2 (63.0 wt%), Al2O3 (17.9 wt%) and Fe2O3 (8.2 wt%). This rock is also characterized by low MgO (2.7 wt%), Na2O (2.4 wt%), TiO2 (0.7 wt%), CaO (1.9 wt%), K2O

(2.1 wt%) and P2O5 (0.1 wt%). The rock is strongly peraluminous (A/CNK = 1.9 and A/NK = 2.9) (Fig. 5 and5b) with Sr/Y = 14.5 and K2O/Na2O = 0.9 (Fig. 5c). The source of the garnetstaurolite-bearing micaschist of Kounoukou defines a trend to the metasediments field (Fig. 5e). The garnet-staurolite-bearing micaschist is enriched in LREE and shows relatively flat HREE patterns (LaN/YbN = 7.5, GdN/YbN = 1.6) with weak negative Eu anomalies (Eu/Eu* = 0.8) (Fig. 6). This garnet-staurolite-bearing micaschist has incompatible trace element patterns characterized by enrichment in LILE such as Rb, Ba and U. It displays positive La and Ce and negative Sr, K, Nb, Ta and Ti anomalies (Fig. 6). In the ternary diagram Al2O3/(FeOt + MgO); 3 * CaO; 5 * (K2O/Na2O) proposed by [START_REF] Laurent | The diversity and evolution of late-Archean granitoids: Evidence for the onset of "modern-style" plate tectonics between 3.0 and 2.5Ga[END_REF], the Kounoukou micaschist falls at the boundary between the sedimentary and high-K mafic rocks source (Fig. 5e).

-Potassic granite of San Pedro

The potassic granite of San Pedro (light orange triangle, Fig. 5a) shows high SiO2 (78.9 wt%) and K2O (5.5 wt%), relatively low Al2O3 (11.5 wt%), MgO (0.3 wt%), Na2O (2.4 wt%), TiO2 (0.1 wt%), Fe2O3 (1.0 wt%), CaO (0.3 wt%), and P2O5 (0.1 wt%). This potassic granite is slightly peraluminous (A/CNK = 1.1 and A/NK = 1.2) (Fig. 5a and5b) with Sr/Y = 7.6 and K2O/Na2O = 2.3 (Fig. 5c). The granite is enriched in LREE and displays a flat HREE pattern (LaN/YbN = 3.8, GdN/YbN = 0.9) and a negative Eu anomaly (Eu/Eu* = 0.8). The analyzed sample is characterized by an enrichment in LILE and negative Nb and Ti anomalies (Fig. 6). et al., 1992) and chondrite normalized REE [START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF]) spidergrams of the studied rocks. For legend, see Fig. 4.

In a normative

Zircon U-Pb geochronology and Hf isotopes -Migmatitic gneiss of San Pedro

The zircon grains obtained from sample SP3B display variable sizes (50 to 300 µm) (Fig. 7a).

In cathodoluminescence (CL) images, the zircon grains show quite heterogeneous internal textures and morphologies. Most grains are euhedral with rounded facets showing magmatic oscillatory zoning, locally overgrown by dark rims. For some of these grains, the oscillatory zoning is blurred by diffuse zones attributed to dissolution-precipitation. Sixty-eight analyses were performed on fifty-three zircons. One other analysis was rejected as containing a very high U concentration >1500 ppm. Thirty-one concordant analyses returned ages ranging from ca. 3241 Ma to ca. 2827 Ma (Fig. 8a,8b). On the probability density plot, the data may be grouped into two main populations including: 1) age cluster from ca. 3241 Ma to ca. 3128 Ma (n = 22) with Th/U between 2.45 and 0.09 but without statistically defined peaks, 2) age cluster from ca. 3113 Ma to ca. 3078 Ma (n = 3), and three isolated analyses returning dates at 2993 ± 32 Ma (Th/U = 0.28), 2975 ± 4 Ma (Th/U = 0.23) and 2827 ± 5 Ma (Th/U = 0.14).

Twenty-three Lu-Hf analyses were performed on concordant zircons of SP3B. The zircons have variable 176 Lu/ 177 Hf ratios (0.00077-0.00790) and 176 Hf/ 177 Hf ratios (0.280428-0.280702) corresponding to subchondritic ℇHf between -9.4 and -0.3. On the plot showing apparent ages obtained for individual zircon vs initial 176 Hf/ 177 Hf composition (Fig. 9a) the data distribution over 9 ℇHf units is particularly marked for the age cluster from ca. 3241 Ma to ca. 3128 Ma and exceeds the accuracy of the analytical technique for this dataset (~3 ℇHf units). All other age clusters exibit a constant and restricted 176 Hf/ 177 Hf ratio between 0.280560 and 0.280680 (~3 ℇHf units), which may be considered as constant considering analytical technique's accuracy.

-Migmatitic gneiss of Monogaga

The zircons from sample SP11 are of variable sizes (50 to 300 µm) (Fig. 7b). The scanning electron microscope (SEM) images of all zircons in sample SP11 show euhedral grains with oscillatory zoning, with few grains showing rounded facets. Some zircon grains show homogeneous overgrowth zones. A few zircon crystals devoid of internal growth zoning, have grown aside a pre-existing core. One hundred and forty-one analyses were performed on one hundred zircons. One hundred and thirty concordant analyses returned ages ranging from ca.

3263 Ma to 2071 Ma (Fig. 8d,8e). The zircons obtained from sample MON4 display variable sizes (50 to 300 µm) (Fig. 7c). The SEM images of all the zircons in the MON4 sample show oscillatory zoning and a high proportion of rounded shapes. Most of the grains are affected by fracturing due to sample processing or radiation damage of the crystal lattice. Forty-eight analyses were performed on forty zircons. Two analyses were filtered away (discordance, high U content, U > 1500 ppm).

The remaining thirty-five analyses yield ages ranging from ca. 3328 Ma to 2815 Ma (Fig. 8g,8h). On the distribution plot, the data may be grouped into two main populations including age spans: 1) a cluster from ca. 3328 Ma to 3156 Ma (n = 22 with Th/U comprised between 0.82 and 0.01 with a clear peak at ca. 3260 Ma but not returning a statistically robust population; 2) a sub-continuous record of ages from ca. 3129 Ma to 2869 Ma (n = 13) with Th/U comprised between 0.05 and 0.00 showing no distinct peak.

Seven Lu-Hf analyses were performed on concordant zircons of MON4. These grains have variable 176 Lu/ 177 Hf ratios of 0.00104-0.00197 with initial 176 Hf / 177 Hf ratios of 0.28071-0.28077 corresponding to superchondritic ℇHf between +0.7 and +3.8 (Fig. 9a). Note that these analyses were solely obtained on zircon cores presenting apparent age comprised between ca.

3230 Ma and 3310 Ma. The initial 176 Hf / 177 Hf ratios remain constant over the period considered and therefore suggest that the sample was affected by a lead loss (Fig 9d ) or a protracted period of zircon dissolution/precipitation and/or crystallization.

-Garnet-cordierite-sillimanite migmatitic gneiss of Grand-Béréby

The zircons obtained from sample GDB8 display variable sizes (50 to 200 µm) (Fig. 7d). The CL images of all the zircons in the GDB8 show oscillatory to complex zoning with rare euhedral shapes. Many grains are rounded. Ninety-three analyses were performed on eighty-seven zircons (Fig. 8j Ten analyses were performed by the Lu-Hf method on concordant zircons of GDB8. The zircons of GDB8 have variable 176 Lu/ 177 Hf ratios of 0.00010-0.00133 with initial 176 Hf/ 177 Hf ratios of 0.28141-0.28155, corresponding to superchondritic ℇHf between 0.0 and +5.5 (Fig. 9e). The spread in initial 176 Hf/ 177 Hf analyses is compatible with a detrital sedimentary origin pointing to several sources (Fig. 9f).

-Garnet-staurolite-bearing micaschist of Kounoukou

The zircons obtained from sample KOU7 display variable sizes (50 to 250 µm) (Fig. 7e). The CL images of all zircons in the KOU7 sample show euhedral elongated shapes with oscillatory magmatic zoning. Few grains display rounded facets. One hundred and nineteen analyses were performed on one hundred and ten zircons (Fig. 8m). Ninety-two concordant analyses returned Th/U = 0.50.

Twenty-three Lu-Hf analyses were performed on concordant zircons of KOU7. The zircons of KOU7 have variable 176 Lu/ 177 Hf ratios of 0.00067-0.00142 with initial 176 Hf/ 177 Hf ratios ranging from 0.281477 and 0.281525, and corresponding to superchondritic ℇHf between +1.5 and +4.9 (Fig. 9e and9g).

-Potassic granite

Sample CIS62 exhibits zircons that vary in sizes (50 to 200 µm) with generally prismatic shapes (Fig. 7f). The CL images show oscillatory magmatic zoning. Sixty-three analyses were obtained from this sample, of which fifty-three are discordant or rich in U (U > 1500 ppm). Nine concordant to near concordant analyses spread in ages from ca. 2312 Ma to ca. 2084 Ma (Fig.

8p, 8q

). These analyses can be grouped as follow: 1) one single analysis dated at 2312 ± 51 Ma with Th/U = 0.99; 2) one single analysis dated at 2205 ± 42 Ma with Th/U = 0.02; 3) one single analysis dated at 2126 ± 12 Ma with Th/U = 0.09; 4) a population ranging from ca. 2105 Ma to 2096 Ma (n = 5) with Th/U comprised between 2.49 and 0.24 returning a weighted mean age of 2100 ± 5 Ma (MSWD = 1.7); 5) one single analysis dated at 2084 ± 6 Ma with Th/U = 0.44.

The date of 2084 ± 6 Ma is tentatively interpreted as the crystalisation age for the potassic granite. The high uncertnainties in the 238 U/ 206 Pb data might be due to a disturbance in the U-Pb system.

Eleven analyses were performed by the Lu-Hf method on concordant zircons of CIS62.

Analyses of CIS62 have variable 176 Lu/ 177 Hf ratios of 0.00029-0.00297 with initial 176 Hf/ 177 Hf ratios ranging from 0.28120 to 0.28151 corresponding to ℇHf values between -8.5 and +6.5 (Fig. 9e). The spread of initial 176 Hf/ 177 Hf with regards to the U/Pb analyses is compatible with two contrasted sources (Fig. 9h). (accuracy) of the instrument, data ploshowing near constant 176 Hf/ 177 Hft).

DISCUSSION

Origin of the metamorphic rocks

Deciphering the nature of the protolith of high-grade gneisses is not always an easy task, especially in case of partial melting.

The mineral assemblage associated with the garnet-staurolite-bearing micaschist of Kounoukou (KOU7) and of the garnet sillimanite migmatitic gneiss from Grand-Béréby (GDB8) points towards a sedimentary (pelitic) origin. Both metapelites display high mean content in Al2O3 (> 15 wt%) and Fe2O3 (> 7 wt%) together with moderate concentration of MgO (> 2 wt%) and low CaO (< 2 wt%). Such compositions are compatible with those of metapelitic rocks [START_REF] Bucher | Metamorphism of Pelitic Rocks (Metapelites)[END_REF].

The potassic granite CIS62 has pronounced negative Nb, Ta, Zr, Hf and Ti anomalies, weak negative Eu anomaly and very low contents in Al2O3, Fe2O3, MgO and CaO compared to all other rocks (Figs. 5 and6). Its high K content suggests a S-type granite , as shown in the ternary diagram Al2O3/(FeOt + MgO); 3 * CaO; 5 * (K2O/Na2O) proposed by [START_REF] Laurent | The diversity and evolution of late-Archean granitoids: Evidence for the onset of "modern-style" plate tectonics between 3.0 and 2.5Ga[END_REF] The migmatitic gneisses of San Pedro and the migmatitic gneiss of Monogaga SP11 cluster in a relatively homogeneous group in compositional and classification diagrams (Fig. 5), while the MON4 gneiss of Monogaga is very different from this group in most of the major element diagrams. Overall, the major element geochemical compositions of migmatitic gneisses are different from those of the metasediments and the potassic granite. On the other hand, the trace and REE patterns are relatively similar for the gneisses and metasediments. The migmatitic gneisses exhibit geochemical compositions of Archean TTGs (SiO2 > 64 wt%, A/CNK ~ 1) as defined by [START_REF] Moyen | Forty years of TTG research[END_REF]. They are enriched in Light Rare-Earth Elements (LREE)

with positive Eu anomalies (Eu/Eu* = 0.64-1.05) and display high Sr/Y ratios. The predominance of quartz and feldspar accounts for the bulk SiO2, Al2O3, Na2O and K2O contents of these rocks, and is consistent with a granodioritic bulk composition. Based on the geochemical data and the character of the U-Pb analyses discussed in detail in Section 6.2, which show two major events (the protolith emplacement at ca. 3250-3200 Ma and ca. 2950-2800 Ma reworking leading to crystallization of the younger zircon population, Fig. 9), we suggest a magmatic protolith of the migmatitic gneisses of San Pedro and Monogaga.

Archean geochronological record of the Sassandra-Cavally domain

The migmatitic gneiss samples from San Pedro (SP3B) and Monogaga (MON4 and SP11) returned a complex age distribution spreading from the the Archean (SP3B, MON4 and SP11)

to the Paleoproterozoic eras (SP11) (Fig. 10). U-Pb analyses acquired on MON4 and SP11 exhibit several concordant date clusters with initial 176 Hf/ 177 Hf ratios that are constant for zircon dates ranging from ca. 3250 Ma and 3000 Ma. The nearly invariant initial 176 Hf/ 177 Hf ratio observed for both samples is characteristic for zircons that have undergone ancient lead-loss [START_REF] Fisher | Accurate Hf isotope determinations of complex zircons using the "laser ablation split stream[END_REF]. Alternatively, this spread of ages may be contributed to a prolonged period of dissolution/precipitation and/or crystallisation in the presence of melt but in a closed system [START_REF] Guergouz | Zircon and monazite petrochronologic record of prolonged amphibolite to granulite facies metamorphism in the Ivrea-Verbano and Strona-Ceneri Zones[END_REF][START_REF] Vanderhaeghe | Secular cooling and crystallization of partially molten Archaean continental crust over 1 Ga[END_REF]. Many of the ages spreading from ca. 3250

Ma and 3000 Ma were obtained on cores of texturally equilibrated zircons with oscillatory zoning. In order to further test the hypothesis of dissolution/precipitation mechanism, systematic core/rim analyses need to be acquired as well as zircon trace element analyses. It was not done in this study and will be better implemented in our futures studies of the rocks from the Archean -Paleoproterozoic boundary terranes. In any case, these features suggest that the protolith of these rocks corresponds to material extracted from the mantle at ca. 3200 Ma.

The age clusters derived from U-Pb analyses in the sample SP3B together with the Hf composition suggest that the younger groups ranging in age from ca. 3113 Ma to 2827 Ma, preserving constant initial 176 Hf/ 177 Hf composition were affected by ancient lead loss or a prolonged period of zircon dissolution/precipitation and/or crystallization. In contrast the age cluster from ca. 3241 Ma to ca. 3128 Ma appears to reflect the mixing of several zircon populations associated with contrasted initial 176 Hf/ 177 Hf composition (Fig. 9b). This may point towards the contribution of diverse zircon sources in the original protholith (magmatic zircons combined with one or more inherited zircon populations). The sparse Hf analyses of zircon that returned apparent zircon ages comprised between ca. 2800 Ma and 3000 Ma either exhibit near constant initial 176 Hf/ 177 Hf (SP3B) or show higher 176 Hf/ 177 Hf ratio (SP11). Whereas the former may also be interpreted as an ancient lead loss event, the latter points towards a zircon producing event ca. 2950 Ma.

For sample SP11 the weighted mean 207 Pb/ 206 Pb age of 3245 ± 4 Ma acquired on the older age cluster is interpreted as the age of the protolith. The analysis showing an apparent age at 2957 ± 11 Ma returned an intial 176 Hf/ 177 Hf ratio of 0.280829 that contrasts with the near constant intial 176 Hf/ 177 Hf ratio obtained on the ca. 3241 and 3078 Ma data cluster (Fig. 9c). The intial 176 Hf/ 177 Hf ratio of 0.280829 is compatible with a zircon producing event at ca. 2950 Ma.

Consequently, the protolith age for SP11 migmatitic gneiss is interpreted to have formed at 3245 ± 4 Ma further affected by a melt crystallization event at ca. 2950 Ma (one analysis returned a concordant age at 2957 ± 11 Ma. The latter event remains poorly constrained as based on a single analysis yet may be indicative of a Mesoarchean migmatitization stage that could have been the driver of the lead loss recorded. More analyses should be conducted on the youngest age population in the sample to further constrain the age of this magmatic event.

For MON4 and SP3B, the spread of ages resulting from ancient lead loss makes it impossible to calculate a statistically robust magmatic age for the protholith. Accordingly, the older 206 Pb/ 207 Pb apparent ages are tentatively proposed as the age of the protolith for both MON4 and SP3B samples and are 3328 ± 13 Ma and 3238 ± 4 Ma, respectively. Note that the complex Hf record for sample SP3B may reflect the presence of inherited xenocrysts in the protolith source which further raise uncertainty for its age attribution.

In the absence of 176 Hf / 177 Hf analysis in MON4 for the younger age cluster it remains difficult to evaluate the nature of the younger age cluster. Yet by analogy with sample SP11, it is proposed that the age of the protolith of ca. 3260 Ma was affected by a melt crystallization event at 2869 ± 13 Ma provided by the apparent age of the youngest zircon.

The ages obtained appear slightly older thant those obtained by Pb-Pb evaporation at 3207 ± 7

Ma acquired on restricted number of zircons collected from the San Pedro gneisses (Kouamelan et al., 1997b[START_REF] Kouamelan | The oldest rock of Ivory Coast[END_REF][START_REF] Kouamelan | Géochronologie et Géochimie des Formations Archéennes et Protérozoïques de la Dorsale de Man en Côte d'Ivoire. Implications pour la Transition Archéen-Protéozoïque[END_REF]. The age discrepancy between the youngest age group may be related to the restricted number of grains analysed using Pb-Pb evaporation.

All the zircons belonging to younger age clusters including the four analyses that were obtained from zircons rims were associated with overall low Th/U ratios < 0.50. Magmatic zircons present Th/U > 0.50 [START_REF] Skublov | Distribution of rare-earth and rare elements in zircons from the miaskite lamproites of the Panozero intrusion in Central Karelia[END_REF][START_REF] Pystin | The early Precambrian history of rock metamorphism in the Urals segment of crust[END_REF][START_REF] Rubatto | Zircon trace element geochemistry: partitioning with garnet and the link between U-Pb ages and metamorphism[END_REF]., while metamorphic zircons have Th/U comprised between 0.10 and 0.30 [START_REF] Pystin | The early Precambrian history of rock metamorphism in the Urals segment of crust[END_REF], or even < 0.10 [START_REF] Rubatto | Zircon trace element geochemistry: partitioning with garnet and the link between U-Pb ages and metamorphism[END_REF]. The age of 2076 ± 7 Ma has been obtained on a large euhedral overgrowth crystallized around an inherited zircon core with an age of 2748 ± 11 Ma (Fig. 7b)

and is likely to represent the age of high-grade metamorphism, possibly in the presence of a silicate melt.

Such Paleoproterozoic overprint is likely to have disturbed further the ancient age record related to the lead loss at ca. 2700 recorded in the same sample (Fig. 8). Accordingly, it is proposed that the San Pedro and Monogaga units represent Paleoarchean protoliths reworked through deformation and metamorphism (including partial melting linked to the migmatitization) in the the Mesoarchean and the Paleoproterozoic.

The age spread recorded in the samples from both localities is similar to that recorded in Sierra Leone, Liberia, and Guinea [START_REF] Barth | Re Os and U Pb geochronological constraints on the eclogite-tonalite connection in the Archean Man Shield, West Africa[END_REF][START_REF] De Waele | New insights on proterozoic tectonics and sedimentation along the peri-Gondwanan West African margin based on zircon U-Pb SHRIMP geochronology[END_REF]Kouamelan et al., 1997b;[START_REF] Thiéblemont | Archean evolution of the Leo Rise and its Eburnean reworking[END_REF] but also in the Reguibat Shield [START_REF] Lahondère | Notice explicative des cartes géologiques et gîtologiques à 1/200 000 et 1/500 000 du Nord de la Mauritanie[END_REF][START_REF] Potrel | Archean crustal evolution of the West African Craton: example of the Amsaga Area (Reguibat Rise). U Pb and Sm Nd evidence for crustal growth and recycling[END_REF]. Across the Sassandra shear zone, Archean rocks were historically ascribed to two main periods of crust formation between ca. 3260-3050 Ma and ca. 2960-2850 Ma [START_REF] Barth | Re Os and U Pb geochronological constraints on the eclogite-tonalite connection in the Archean Man Shield, West Africa[END_REF][START_REF] De Waele | New insights on proterozoic tectonics and sedimentation along the peri-Gondwanan West African margin based on zircon U-Pb SHRIMP geochronology[END_REF]Kouamelan et al., 1997b;[START_REF] Rollinson | Archaean crustal evolution in West Africa: A new synthesis of the Archaean geology in Sierra Leone, Liberia, Guinea and Ivory Coast[END_REF][START_REF] Thiéblemont | Archean evolution of the Leo Rise and its Eburnean reworking[END_REF]. The results obtained here further document this two-staged period with initial crust extration at about ca. 3300-3250 Ma followed by a major lead loss event at ca. 2960-2850 Ma.

The nature of the magmatic and metamorphic processes underlying the generation of these two broad populations remains largely unknown. zircon ℇHf between +1.5 to -4.6 and +0.3 and -9.4 to -0.3 respectively (Fig. 11). These results point toward an early juvenile crust extraction at ca. 3300 Ma (MON4) immediately followed by reworking of older crustal components (SP11 and SP3B) the latter being highlighted by highly negative ℇHf values down to -9.4 (Fig. 9a).

Whereas slightly positive and negative ℇHf values may be related to the reworking of material emplaced at ca. 3300 Ma (MON4), the recorded ℇHf values for San Pedro sample (SP3B), extending to -9.4, are indicative of the reworking of an even older crustal precursor (Fig. 9).

Depleted Mantle Hf model ages are severely limited by the multiple, unconstrained assumptions and uncertainties that tend to produce a bias towards artificially old model ages [START_REF] Vervoort | Clarifying the zircon Hf isotope record of crust-mantle evolution[END_REF]. Accordingly, it is difficult to evaluate the age of the crustal precursor that contributed to the magmatic process.

One may assume the extraction of enriched material from the mantle early on, followed by the transformation of this dominantly basaltic protocrust into something progressively more felsic from ca. 3.8 Ga (e.g., [START_REF] Patchett | Nd isotopes and tectonics of 1.9-1.7 Ga crustal genesis[END_REF][START_REF] Veizer | Basement and sedimentary recycling and continental evolution[END_REF][START_REF] Vervoort | No significant production of continental crust prior to 3.8 Ga[END_REF] (Fig. 9.). Using a 176 Lu/ 177 Hf = 0.0115 age range for the precursor from which the zircons with negative ℇHf values may be loosely constrained as a Meso to Paleoarchean source (Fig. 9). Ages of the continental crust formation were obtained in the south-western part of the West African Craton (Kenema-Man domain) as early as ca. 3500 Ma [START_REF] Thiéblemont | A 3.5 Ga granite-gneiss basement in Guinea: further evidence for early archean accretion within the West African Craton[END_REF]. Further U-Pb evaporation zircon ages acquired in the Reguibat shield suggest a crustal growth period of the WAC prior to 3515 ± 15 Ma [START_REF] Potrel | 3.5 Ga old terranes in the West African craton, Mauritania[END_REF]. While beyond the scope of this study, it potassic peraluminous granitic composition similar to the one intruding into the northern margin of the Archean Kenema-Man domain [START_REF] Eglinger | New insights into the crustal growth of the Paleoproterozoic margin of the Archean Kéména-Man domain, West African craton (Guinea): Implications for gold mineral system[END_REF]. Metamorphic reworking of Archean rocks during the Paleoproterozoic was also reported in the zone of Man [START_REF] Caby | Lithology, structure and metamorphism of the Birimian formations in the Odienné area (Ivory Coast): the major role played by plutonic diapirism and strike-slip faulting at the border of the Man Craton[END_REF]Kouamelan et al., 1997b;[START_REF] Pitra | Palaeoproterozoic high-pressure granulite overprint of the Archean continental crust: evidence for homogeneous crustal thickening (Man Rise, Ivory Coast)[END_REF][START_REF] Triboulet | Les métabasites birimiennes et archéennes de la région de Toulepleu-Ity (Côte-d'lvoire): des roches portées à 8 kbar (≈ 24 km) et 14 kbar (≈ 42 km) au Paléoprotérozoïque[END_REF] 20 Myrs) between the sediment deposition and their burial and metamorphism in the nearby Kedougou-Kenieba Inlier [START_REF] Kone | Source and deposition age of the Dialé-Daléma metasedimentary series (Kédougou-Kéniéba Inlier, Senegal) constrained by U-Pb geochronology on detrital zircon grains[END_REF]. Interestingly, no Archean detrital zircons with ages corresponding to the ages found in the migmatitic gneisses were identified there except for only one grain yielding 2670 ± 11 Ma.

The results from our study further document the major crustal reworking process, including that of ancient Archean crustal domains that took place at the later stages of the Eburnean orogeny.

Detrital zircons from both metasediments (garnet-cordierite-sillimanite migmatitic gneiss of Grand-Béréby, GDB8 and garnet-staurolite-bearing micaschist of Kounoukou, KOU7) returned ℇHf values between +0.0 and +5.5. Such ℇHf data highlights the broadly juvenile signature and echoes with results obtained in the Baoule-Mossi domain [START_REF] Parra-Avila | The geochronological evolution of the Paleoproterozoic Baoulé-Mossi domain of the southern West African Craton[END_REF]. In contrast, the ca. 2086 Ma old potassic granite (CIS62) intruding the San Pedro gneissic unit exhibits a population of inherited zircons with a hybrid Hf isotopic signature. In this rock, ℇHf form two distinct clusters between -4.9 and -8.5 (n = 6) and between +1.9 and +6.5 (n = 3) for zircons formed between ca. 2343 to 2100 Ma. Zircons with strongly negative ℇHf are darker in CL images than those with positive ℇHf which show lighter character in CL images. This hybrid isotopic signature is pointing towards both Paleoproterozoic juvenile input and reworking of pre-existing, likely Archean, crust. The model ages for the Archean protolith(s) is broadly estimated between about 3.3 and 3.1 Ga (Fig. 9). This age bracket is consistent with the age distribution provided by the SASCA Archean gneisses. These results also echo with those obtained from the northern transect across the Kenema-Man domain margin. There, the inherited crustal reworking signature is further highlighted by the presence of inherited Archean zircons with U-Pb ages between ca. 2.87 and 3.09 Ga [START_REF] Eglinger | New insights into the crustal growth of the Paleoproterozoic margin of the Archean Kéména-Man domain, West African craton (Guinea): Implications for gold mineral system[END_REF].

Regional implication

The Ma. In the northern part of the Archean Kenema-Man domain, close to the limit of the Proterozoic Baoulé-Mossi domain of Guinea, the terranes appear to be largely reworked at ca. 2100 Ma [START_REF] Eglinger | New insights into the crustal growth of the Paleoproterozoic margin of the Archean Kéména-Man domain, West African craton (Guinea): Implications for gold mineral system[END_REF]. The presence of Archean xenocrysts in Paleoproterozoic granitic intrusions further suggests some degree of involvement of the Archean crust during the formation of Paleoproterozoic granitic magmas [START_REF] Abati | Insights on the crustal evolution of the West African Craton from Hf isotopes in detrital zircons from the Anti-Atlas belt[END_REF][START_REF] Begg | The lithospheric architecture of Africa: Seismic tomography, mantle petrology, and tectonic evolution[END_REF][START_REF] Block | Paleoproterozoic juvenile crust formation and stabilisation in the south-eastern West African Craton (Ghana); New insights from U-Pb-Hf zircon data and geochemistry[END_REF][START_REF] Petersson | Zircon U-Pb-Hf evidence for subduction related crustal growth and reworking of Archaean crust within the Palaeoproterozoic Birimian terrane, West African Craton, SE Ghana[END_REF][START_REF] Petersson | Extensive reworking of Archaean crust within the Birimian terrane in Ghana as revealed by combined zircon U-Pb and Lu-Hf isotopes[END_REF]. For example, Archean zircons between ca. 3.0 and 3.4

Ga were found in the Boboti pluton in the Kedougou-Kenieba Inlier [START_REF] Lambert-Smith | Palaeotectonic setting of the south-eastern Kédougou-Kéniéba Inlier, West Africa: New insights from igneous trace element geochemistry and U-Pb zircon ages[END_REF].

The Archean influence on crustal development in the West African Craton is also well documented in the southeast Baoulé Mossi domain. In Ghana, the Winneba pluton returned ℇHf and ℇNd values, indicative of an Archean crustal contribution [START_REF] Leube | The early Proterozoic Birimian Supergroup of Ghana and some aspects of its associated gold mineralization[END_REF][START_REF] Taylor | Early Proterozoic crustal evolution in the birimian of Ghana: constraints from geochronology and isotope geochemistry[END_REF]. In-situ analyses conducted in Ghana highlighted ℇHf zircon signature attesting of a shortlived period of crustal reworking at ca. 2140 to 2130 Ma following an Eoeburnean (ca. 2250

Ma) juvenile accretion [START_REF] Block | Paleoproterozoic juvenile crust formation and stabilisation in the south-eastern West African Craton (Ghana); New insights from U-Pb-Hf zircon data and geochemistry[END_REF][START_REF] Petersson | Zircon U-Pb-Hf evidence for subduction related crustal growth and reworking of Archaean crust within the Palaeoproterozoic Birimian terrane, West African Craton, SE Ghana[END_REF][START_REF] Petersson | Extensive reworking of Archaean crust within the Birimian terrane in Ghana as revealed by combined zircon U-Pb and Lu-Hf isotopes[END_REF].

The identification of Archean relics within the Sassandra-Cavally domain east of the Sassandra regional boundary and in southeastern Ghana [START_REF] Petersson | Zircon U-Pb-Hf evidence for subduction related crustal growth and reworking of Archaean crust within the Palaeoproterozoic Birimian terrane, West African Craton, SE Ghana[END_REF] highlights the prevalence of Archean blocks of various sizes and their influence on Paleoproterozoic crustal evolution. In the Sassandra-Cavally domain, the late magmatic reworking at ca. 2080 Ma is broadly coeval with that observed in the northern edge of the Kenema-Man domain, where granites analysed in the Suhum basin [START_REF] Petersson | Zircon U-Pb-Hf evidence for subduction related crustal growth and reworking of Archaean crust within the Palaeoproterozoic Birimian terrane, West African Craton, SE Ghana[END_REF] suggest significant reworking of Archean rocks starting from ca. 2113 Ma. Such time lag may attest to a diachronic assembly of several Archean blocks with a westward migration of the magmatic front over the Eburnean orogeny [START_REF] Parra-Avila | The geochronological evolution of the Paleoproterozoic Baoulé-Mossi domain of the southern West African Craton[END_REF] and further support a collisional tectonic model involving the docking between Archean and Paleoproterozoic blocks resulting in large-scale crustal thickening (Allibone et al., 2002, in press;[START_REF] Eglinger | New insights into the crustal growth of the Paleoproterozoic margin of the Archean Kéména-Man domain, West African craton (Guinea): Implications for gold mineral system[END_REF][START_REF] Feybesse | The paleoproterozoic Ghanaian province: Geodynamic model and ore controls, including regional stress modeling[END_REF][START_REF] Feybesse | The Archaean/Proterozoic contact zone in West Africa: a mountain belt of décollement thrusting and folding on a continental margin related to 2.1 Ga convergence of Archaean cratons?[END_REF][START_REF] Grenholm | A geodynamic model for the Paleoproterozoic[END_REF][START_REF] Koffi | Evolution tectono-métamorphique du Craton Ouest Africain : Exemple du secteur de Grand-Béréby a Sassandra (Sud-Ouest de la Côte d'Ivoire)[END_REF][START_REF] Wane | The onset of the Eburnean collision with the Kenema-Man craton evidenced by plutonic and volcanosedimentary rock record of the Masssigui region, southern Mali[END_REF]. ). Yet, a more complex scenario involving a prolonged period of dissolution/precipitation and/or cristallisation in the presence of melt over that period cannot be completely rulled out.

In Grand-Béréby and Kounoukou metasedimentary rocks were affected by high-temperature metamorphism reaching partial melting. U-Pb ages on zircons range from ca. 2213 to 2088 Ma with ℇHf values ranging from +0.0 to +5.5. These data suggest a second major period of crustal growth at this time. The granitic sample of the San Pedro area, dated at 2084 ± 6 Ma, exhibits a hybrid isotopic signature with ℇHf values forming two distinct clusters between -4.9 and -8.5 and between +2.2 and +6.5 for inherited zircon grains dated between ca. 2343 to 2100 Ma. This is indicative of a mixed signature involving reworking of Archean domains and juvenile Paleoroterozoic input. The San Pedro granite intrusion is coeval with peak metamorphic conditions and the migmatitisation of the Monogaga Archean gneiss, which is dated at 2076 ± 6 Ma. This age is within error of the youngest Proterozoic ages identified in KOU7 (2082 ± 4

Ma) and GDB8 (2069 ± 4 Ma). These young ages may accordingly reflect metamorphism rather than maximum deposition age. By comparison, in the Baoulé-Mossi domain the plutonic activity occurred between ca. 2250 and ca. 2060 Ma (Agyei et al., 2009;[START_REF] Delor | Peri-plutonic gravity driven deformations and transcurrent tectonics between 2.2 and 2.1 By: a case study from the Birimian Cycle in Ivory Coast[END_REF][START_REF] Feybesse | The paleoproterozoic Ghanaian province: Geodynamic model and ore controls, including regional stress modeling[END_REF][START_REF] Lahondère | First evidence of early Birimian (2.21 Ga) volcanic activity in Upper Guinea: the volcanics and associated rocks of the Niani suite[END_REF][START_REF] Schwartz | The Perkoa zinc deposit, Burkina Faso[END_REF][START_REF] Tshibubudze | Oldest U-Pb crystallisation age for the West African Craton From the Oudalan-Gorouol Belt of Burkina Faso[END_REF][START_REF] Liégeois | Short-lived Eburnian orogeny in southern Mali. Geology, tectonics, U-Pb and Rb-Sr geochronology[END_REF][START_REF] Parra-Avila | Zircon Hf and O-isotope constraints on the evolution of the Paleoproterozoic Baoulé-Mossi domain of the southern West African Craton[END_REF], 2017;[START_REF] Thébaud | The Paleoproterozoic (Rhyacian) gold deposits of West Africa[END_REF][START_REF] Tshibubudze | Oldest U-Pb crystallisation age for the West African Craton From the Oudalan-Gorouol Belt of Burkina Faso[END_REF][START_REF] Eglinger | New insights into the crustal growth of the Paleoproterozoic margin of the Archean Kéména-Man domain, West African craton (Guinea): Implications for gold mineral system[END_REF][START_REF] Mériaud | Lithostratigraphic evolution of the Bandamian Volcanic Cycle in central Côte d'Ivoire: Insights into the late Eburnean magmatic resurgence and its geodynamic implications[END_REF]. The ages of emplacement of felsic intrusions in the Baoulé-Mossi domain are associated with two orogenic cycles namely the Eoeburnean orogeny (ca. 2250-2150 Ma) and the Eburnean orogeny (ca. 2135-2100 Ma) [START_REF] Liégeois | Short-lived Eburnian orogeny in southern Mali. Geology, tectonics, U-Pb and Rb-Sr geochronology[END_REF][START_REF] Parra-Avila | Zircon Hf and O-isotope constraints on the evolution of the Paleoproterozoic Baoulé-Mossi domain of the southern West African Craton[END_REF], 2017;[START_REF] Thébaud | The Paleoproterozoic (Rhyacian) gold deposits of West Africa[END_REF][START_REF] Tshibubudze | Oldest U-Pb crystallisation age for the West African Craton From the Oudalan-Gorouol Belt of Burkina Faso[END_REF]. It has been proposed that the docking of the Leo-Man shield onto the Baoulé-Mossi domain occurred from ca. 2095 Ma and may coincide with a period of lithospheric delamination leading to the widespread emplacement of potassic two-mica granites [START_REF] Eglinger | New insights into the crustal growth of the Paleoproterozoic margin of the Archean Kéména-Man domain, West African craton (Guinea): Implications for gold mineral system[END_REF] as well as extrusive bi-modal volcanism [START_REF] Mériaud | Lithostratigraphic evolution of the Bandamian Volcanic Cycle in central Côte d'Ivoire: Insights into the late Eburnean magmatic resurgence and its geodynamic implications[END_REF]. The second period of crustal growth recorded in the SASCA domain is highlighting the influence of this thermal event.

Our conclusions further highlight the local contribution of Archean crustal domains in the foundation of the West African Craton in the Paleoproterozoic [START_REF] Begg | The lithospheric architecture of Africa: Seismic tomography, mantle petrology, and tectonic evolution[END_REF][START_REF] Parra-Avila | The Eburnean magmatic evolution across the Baoule-Mossi domain: geodynamic implications for the West African Craton[END_REF], 2016;[START_REF] Petersson | Extensive reworking of Archaean crust within the Birimian terrane in Ghana as revealed by combined zircon U-Pb and Lu-Hf isotopes[END_REF]. The proportion of the Archean reworked crustal component, documented by both U-Pb zircon ages and Hf model ages, seems to be more important than was registered by the Sm/Nd isotopic system, which suggested exclusively a Paleoproterozoic juvenile character of these rocks [START_REF] Boher | Crustal growth in West Africa at 2[END_REF]. The West African Craton consists in the assembly of Paleoarchean and Neoarchean crustal domains that were partially reworked in the Paleoproterozoic during the Eburnean orogeny.

Fig. 1 .

 1 Fig. 1. (A) Simplified geological map of the West African Craton (modified after Grenholm,

Fig. 3 .

 3 Fig. 3. Leucosome veins concordant or discordant to the S2 foliation in the San Pedro migmatitic gneisses (a, b and c) and Grand-Béréby (d). Potassic granite intersects the S2 foliation and is emplaced along the E-W oriented shear zones (c).

  (a) MGSP: Migmatitic gneiss of San Pedro, MGM: Migmatitic gneiss of Monogaga, GCSMGGB: Garnet-cordierite-sillimanite migmatitic gneiss of Grand-Béréby, GSMK: Garnet-staurolite-bearing micaschist of Kounoukou, PGSP: Potassic granite of San Pedro. (b) DL: Detection Limit. (c) Latitude-Longitude of the sample in the WGS84 coordinate system.

Fig. 4 .

 4 Fig. 4. Photographs and microphotographs showing the studied rocks of the Sassandra-Cavally domain. Abbreviations: q = quartz; pl = plagioclase; bi = biotite; g = garnet; kfs = K-feldspar; mu = muscovite; mnz = monazite, sill = sillimanite, tur = tourmaline, hb = hornblende, st = staurolite, cd = cordierite, ep = epidote and ilm = ilmenite.

P2O5 ( 0

 0 .02-0.2 wt%) show comparable values. They are slightly peraluminous (A/CNK = 1.04-1.15 and A/NK = 1.59-2.03) (Fig.5b) with the K2O/Na2O comprised between 0.35 and 0.53.The Sr/Y ratio is comprised between 11.3 and 27.4, with the exception of sample Bal 2-4, which shows anomalously high values (96.5) (Fig.4c). In a normative An-Ab-Or classification diagram[START_REF] O'connor | A classification for quartz-rich igneous rocks based on feldspar ratio[END_REF], migmatitic gneisses correspond to granodiorite (three samples), trondhjemite (one sample), and granite (one sample) (Fig.5d). The ternary diagram Al2O3/(FeOt + MgO); 3 * CaO; 5 * (K2O/Na2O) proposed by[START_REF] Laurent | The diversity and evolution of late-Archean granitoids: Evidence for the onset of "modern-style" plate tectonics between 3.0 and 2.5Ga[END_REF] defines a magmatic source ranging from high-K to low-K mafic rocks (Fig.5e). The migmatitic gneisses of San Pedro are enriched in lithophile elements (LILE) (Rb, Th, U) and overall yield positive Th anomalies and negative K, Nb and Ti anomalies (Fig.6). The gneisses are enriched in light Rare-Earth Elements (LREE) and display LaN/YbN = 11.6-65.9, and GdN/YbN = 1.4-3.8.

  7 and A/NK = 1.7) with Sr/Y = 7.6 and K2O/Na2O = 0.2 values while SP11 is slightly peraluminous (A/CNK = 1.0 and A/NK = 2.2) (Fig. 5b), with Sr/Y = 34.7 and K2O/Na2O = 0.5 values (Fig. 5c). In a normative An-Ab-Or classification diagram (O'Connor, 1965), migmatitic gneisses of Monogaga correspond to a tonalite and a grandiorite (Fig. 5d). The diagram of Laurent et al. (2014) defines a magmatic source for the Monogaga migmatitic gneisses close the boundary of the high-K to low-K mafic rocks (Fig. 5e). The migmatitic gneisses of Monogaga are enriched in light Rare-Earth Elements (LREE) with MON4 (LaN/YbN = 4.8, GdN/YbN = 1.2) less fractionated in LREE than SP11 (LaN/YbN = 44.2, GdN/YbN = 4.5). MON4 has a very slightly positive (1.1) and SP11 displays a weak negative (0.7) Eu/Eu* anomaly. Both samples are enriched in lithophile elements (LILE) (Rb, Th, U) and are marked overall by positive Th

  5e). The garnet-cordierite-sillimanite migmatitic gneisses of Grand-Béréby are enriched in LREE and show relatively flat HREE patterns (LaN/YbN = 4.4-13.1, GdN/YbN = 1.2-2.2) with weak negative Eu anomalies (Eu/Eu* = 0.7-0.8) (Fig.6). They have incompatible trace element patterns characterized by enrichment in LILE such as Rb, Ba and U. They display positive La, Th and Ce and negative Sr, K, Ta and Ti anomalies (Fig.6). In the ternary diagram Al2O3/(FeOt + MgO); 3 * CaO; 5 * (K2O/Na2O) proposed by[START_REF] Laurent | The diversity and evolution of late-Archean granitoids: Evidence for the onset of "modern-style" plate tectonics between 3.0 and 2.5Ga[END_REF], the Grand-Béréby samples are clearly distinct from the migmatitic gneisses of San Pedro and Monogaga and they

  An-Ab-Or classification diagram (O'Connor, 1965), the potassic granite corresponds to a granite. (Fig.5d). The ternary diagram Al2O3/(FeOt + MgO); 3 * CaO; 5 * (K2O/Na2O) proposed by[START_REF] Laurent | The diversity and evolution of late-Archean granitoids: Evidence for the onset of "modern-style" plate tectonics between 3.0 and 2.5Ga[END_REF] suggests the partial melting of a crustal source of sedimentary origin (S-type) (Fig.5e).

Fig. 5 .

 5 Fig. 5. Major element geochemistry of the studied rocks in Harker diagrams (a), in an A/NK vs. A/CNK diagram (b), K2O/Na2O vs. Sr/Y diagram (c). Normative An-Ab-Or triangle (O'Connor, 1965) showing the migmatitic gneiss composition of San Pedro and Monogaga (d) and (e) ternary diagram Al2O3/(FeOt + MgO); 3 * CaO; 5 * (K2O/Na2O) of Laurent et al. (2014) on which the composition of the migmatitic gneisses of San Pedro and Monogaga is plotted.

Fig. 6 .

 6 Fig.6. Primitive mantle-normalized trace element[START_REF] Mcdonough | Potassium, rubidium, and cesium in the Earth and Moon and the evolution of the mantle of the Earth[END_REF] and chondrite normalized REE[START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF]) spidergrams of the studied rocks. For legend, see Fig.4.

Fig. 7 .

 7 Fig. 7. Cathodoluminescence (CL) images of representative zircons grains from the studied rocks. Circles indicate the location of U-Pb analyses.

Fig. 7 .

 7 Fig. 7. (continued).

Fig. 8 .

 8 Fig. 8. U/Pb concordia diagrams (left) and distribution plots (right) for zircon of all samples dated using LA-ICPMS. For each sample, in the main concordia diagram, the analyses filled in red have a concordance between -2% and +5%, and the white filled analyses are discordant and not selected for interpretation. In the inset diagram, the concordant to near-concordant analyses are color coded following U concentration. (a, b, c) Sample SP3B, migmatitic gneiss from San

Fig. 8 .

 8 Fig. 8. (continued).

Fig. 9 .

 9 Fig. 9. Compilation of zircon U-Pb and Lu-Hf data obtained in the course of this study. (a and e): ℇHf (t) vs. apparent 207 Pb/ 206 Pb age diagrams for individual spots for migmatitic gneiss of San Pedro SP3B and Monogaga SP11, MON4 (a), garnet-cordierite-sillimanite migmatitic gneiss of Grand-Béréby GDB8, garnet-staurolite-bearing micaschist of Kounoukou KOU7 and potassic granite CIS62 (e). (b, c, d, f, g and h): 176 Hf/ 177 Hft vs. apparent 207 Pb/ 206 Pb age diagrams for individual spots of zircon from the migmatitic gneiss of San Pedro SP3B (b), Monogaga SP11 (c), MON4 (d), garnet-cordierite-sillimanite migmatitic gneiss of Grand-Béréby GDB8 (f), garnet-staurolite-bearing micaschist of Kounoukou KOU7 (g) and potassic granite CIS62 (h). Crustal evolution trends are calculated with a value of 176 Lu/ 177 Hf = 0.0115, value for average present-day continental crust. CHUR = chondritic uniform reservoir; DM = depleted mantle after Vervoort et al. (2018). Red square indicating the external reproducibility

Fig. 10 .

 10 Fig. 10. ℇHf (t) and probability density plots for all U-Pb zircon data acquired on the samples. (a) migmatitic gneiss of Monogaga MON4; (b) migmatitic gneiss of San Pedro SP3B; (c) migmatitic gneiss of Monogaga SP11; (d) garnet-cordierite-sillimanite migmatitic gneiss of Grand-Béréby GDB8; (e) garnet-staurolite-bearing micaschist of Kounoukou KOU7 and (f) potassic granite of San Pedro CIS62.

Fig. 11 .

 11 Fig. 11. ℇHf(t) vs. 207 Pb/ 206 Pb age diagrams showing the ages of the protoliths of the San Pedro and Monogaga migmatitic gneisses and the San Pedro potassic granite.

  net influence of pre-existing Archean crust on the overall crustal evolutionary process in this Paleoproterozoic part of the West African Craton remains elusive, with most of the Baoulé-Mossi domain dominated by Proterozoic juvenile isotopic signature. Yet, the Lu-Hf isotopic data acquired in the Southern Mali and Western Burkina Faso by Parra-Avila et al. (2017) further indicate the local contribution of older crustal material potentially as old as ca. 2800

  The absence of Archean xenocrysts of the ages of the migmatitic gneisses of San Pedro and Monogaga (~3200-2800 Ma) in the Kounoukou misaschist and the Grand Béréby paragneiss is noteworthy as these lithologies are adjacent today. Such absence raises the question of the nature and timing of the contact between the Archean gneisses and Paleoproterozoic metasediments of the Sassandra-Cavally domain and suggests the sediments did not source the Archean basement. The two domains were assembled by collisional tectonics later during the Eburnean orogeny, which is documented by similar metamorphic ages in the migmatitic gneisses (2076 ± 6 Ma) and metasediments (from 2082 ± 4 Ma to 2069 ± 4 Ma) along with the magmatic age (2084 ± 6 Ma) of the potassic granite intruding the gneisses. Such relationship may be seen as key to further unravel tectonic process leading to the craton assembly. CONCLUSION U-Pb and Lu-Hf isotope analyses on zircon from rocks of the SASCA domain located to the east of the Sassandra shear zone (Archean-Paleoproterozoic transition zone) allows to further constrain the timing of the continental crust extraction and illustrates the protracted crustal stabilization process that contributed to the emergence of continental landmasses in the Precambrian. The migmatitic gneisses of San Pedro and Monogaga contain essentially Archean zircons (U-Pb ages of ca. 3328 to 2812 Ma) with ℇHf values ranging from -12.6 to +3.8, pointing to early crustal growth and reworking of older, possibly Paleoarchean, crustal precursors. The spread of ages combined with 176 Hf/ 177 Hft obtained on the Archean migmatitic gneiss point towards a 3.3 Ga age for the protolith followed by a 2.8 Ga led loss event (early migmatitization

Table 1 :

 1 Whole rock major and trace element composition.

				MGSP a			MGM a		GCSMGGB a		GSMK a	PGSP a	DL b
	Sample	SP3B	Bal 1-2	Bal 2-4	Por 1	SP 1B	SP 11	MON4	GDB8	GDB3	GDB4	GDB5	CIS63	CIS62
	WGS 84
	coordinate
	system
	Lat c	4.72295 4.72076 4.72299 4.74307 4.73089	4.79892 4.80868	4.72122 4.64294 4.65084 4.64521	4.82163	4.72084
	Long c	-6.6395 -6.6508 -6.6392 -6.6199 -6.6389	-6.4423	-6.441	-6.9533 -6.9174 -6.9202 -6.9166	-6.3978	-6.6504
	wt% d
	SiO2	68.89	64.90	71.20	67.80	68.90	66.70	55.90	56.40	63.30	65.00	61.90	63.00	78.86	0.01
	TiO2	0.48	0.57	0.34	0.42	0.38	0.47	0.46	0.99	0.85	0.72	0.68	0.69	0.059	0.001
	Al2O3	15.09	16.30	13.80	15.90	15.70	15.30	14.40	19.60	18.10	17.50	15.20	17.90	11.51	0.01
	Fe2O3	4.48	5.62	3.87	4.51	3.51	4.65	10.40	10.40	8.98	8.41	9.84	8.16	1.01	0.01
	MnO	0.069	0.08	0.04	0.06	0.05	0.05	0.19	0.12	0.09	0.09	0.13	0.07	0.007	0.001
	MgO	1.3	1.77	2.30	1.19	1.54	2.25	5.32	3.92	2.70	2.15	3.13	2.73	0.25	0.01
	CaO	2.73	4.05	1.88	4.05	2.83	3.12	8.62	1.97	1.25	1.35	2.58	1.88	0.33	0.01
	Na2O	4.07	3.93	3.88	3.82	4.87	4.07	3.48	3.19	1.97	2.23	3.08	2.41	2.41	0.01
	K2O	1.63	1.83	2.05	1.44	1.72	2.20	0.77	2.20	2.12	1.94	2.24	2.09	5.53	0.01
	P2O5	0.17	0.22	0.02	0.18	0.14	0.19	0.05	0.08	0.05	0.06	0.22	0.13	0.05	0.01
	LOI	1.42	0.09	0.40	0.18	0.11	0.30	0.35	0.41	0.12	0.09	0.37	0.47	0.72	0.01
	Total	100.3	99.36	99.78	99.55	99.75	99.30	99.94	99.28	99.53	99.54	99.37	99.53	100.7	0.01
	ppm d
	Cs	2.8	3.30	1.80	0.70	2.10	0.40	0.09	2.30	1.50	0.90	3.00	8.50	0.8	0.1
	Rb	91	98.20	90.60	55.10	73.70	121.60	4.50	172.80	99.50	116.50	132.90	75.20	106	1
	Ba	239	286.00	375.00	439.00	159.00	369.00	114.00	357.00	575.00	271.00	367.00	679.00	748	2
	Th	24.1	16.50	19.10	9.10	16.10	13.90	2.10	7.70	7.80	7.70	5.90	4.10	8.57	0.05
	Nb	13.2	17.40	6.00	8.90	10.20	10.00	3.20	12.30	7.90	7.60	7.70	5.90	1.8	0.2
	Pb	25	5.10	3.20	2.30	3.80	2.10	1.60	2.60	1.60	2.00	3.50	1.60	39	0.1
	Sr	235	330.20	424.70	328.40	234.10	301.70	126.90	237.00	242.00	173.20	273.60	269.30	168	2
	Zr	241	220.90	193.50	240.80	199.00	117.30	92.30	162.80	214.00	158.40	226.80	121.40	12	1
	Y	20.8	22.60	4.40	12.00	13.00	8.70	16.60	18.20	24.10	22.60	34.20	18.60	22	0.5
	V	47	77.00	34.00	37.00	51.00	63.00	157.00	175.00	144.00	126.00	111.00	145.00	6	5
	Ni	19.9	16.80	6.30	7.20	6.50	30.80	35.60	92.70	71.40	61.50	53.00	53.60	< 20	0.1
	Hf	5.4	5.60	5.10	5.10	4.80	3.00	2.40	4.60	5.90	4.40	5.80	3.40	0.3	0.1
	Sn	3	3.00	2.00	1.00	2.00	2.00	1.00	4.00	2.00	2.00	1.00	0.90	< 1	1
	Ta	2.72	2.40	0.30	0.60	0.80	0.40	0.40	0.90	0.40	0.40	0.90	0.50	0.12	0.01
	U	3.59	3.70	1.50	2.70	2.60	0.40	0.90	2.00	0.80	1.60	2.10	1.30	1.43	0.01
	W	0.49	0.49	0.49	0.49	0.49	0.49	0.49	0.49	0.49	0.49	0.70	0.49	2.2	0.5
	La	67.5	43.90	41.00	36.50	37.60	36.90	13.00	31.30	36.30	32.80	25.00	22.00	10.8	0.05
	Ce	120	79.10	69.40	62.70	62.50	66.60	20.20	66.00	76.30	67.80	51.30	45.10	20.3	0.05
	Pr	12.4	8.99	6.64	5.71	6.49	6.94	2.51	7.20	8.53	7.59	5.88	5.50	2.1	0.01
	Nd	42.1	30.70	21.50	17.80	21.10	23.50	9.90	28.00	32.10	29.00	23.80	20.60	7.62	0.05
	Sm	6.98	5.24	2.82	2.81	3.49	4.09	2.25	5.02	6.03	5.51	4.82	4.12	1.79	0.01
	Eu	1.29	1.19	0.73	0.89	0.86	0.82	0.84	1.26	1.31	1.19	1.31	1.03	0.51	0.005
	Gd	5.53	4.37	1.92	2.54	3.10	3.12	2.72	4.36	5.41	4.70	5.75	3.90	2.23	0.01
	Tb	0.76	0.63	0.19	0.34	0.43	0.38	0.47	0.65	0.80	0.72	1.00	0.57	0.45	0.01
	Dy	3.99	3.74	0.89	2.08	2.48	1.91	3.01	3.54	4.34	4.05	6.26	3.31	2.98	0.05

  On the data distribution plot, several age populations are distinguished : 1) an age cluster from ca. 3263 Ma to 3234 Ma (n = 18) with Th/U comprised between 0.43 and 0.27 and giving a weighted mean age of 3245 ± 4 Ma (MSWD = 1.6); 2) a nearly continuous record from ca. 3226 Ma to 3124 Ma (n = 64) with a potential peak around ca. 3200 Ma and Th/U values between 0.52 and 0.20; 3) an age cluster from ca. 3108 Ma to 3076 Ma (n = 10) with Th/U ratio ranging between 0.49 and 0.20; 4) a sub-continuous record of ages from ca. 3057 Ma to 2984 Ma (n = 11) with Th/U comprised between 0.41 and 0.18 showing a distinct peak at about ca. 3020 Ma; 5) an age cluster from ca. 2965 Ma to 2823 Ma (n = 13) showing a distinct peak at about 2832 Ma; 6) a sub-continuous record of ages from ca.2787 Ma to 2695 Ma (n = 9) and Th/U comprised between 0.18 and 0.01; and 7) an age cluster from ca. 2082 Ma to 2071 Ma (n = 4) and Th/U comprised between 0.21 and 0.06 and giving a weighted mean age of 2076 ± 7 Ma (MSWD = 0.45). The zircon cores belonging to the oldest age cluster from ca. 3241 and 3078 Ma returned Th/U between 0.43 and 0.27.Sixteen analysis points were performed to analyse the Lu-Hf isotope composition on concordant zircons of SP11. The zircons of SP11 have variable 176 Lu/ 177 Hf ratios of 0.00057-0.00104 with, however, relatively homogeneous 176 Hf/ 177 Hf ratios of 0.280696-0.280829

corresponding to superchondritic ℇHf between -4.1 and +1.9. On the plot showing apparent ages obtained for individual zircon vs initial 176 Hf/ 177 Hf composition (Fig.

9a

), zircon cores dated between ca. 3241 and 3078 Ma present initial 176 Hf/ 177 Hf that spread over two ℇHf units, remaining within the precision of the analytical technique. Taken conjointly, these results show a nearly constant initial 176 Hf/ 177 Hf composition over ca. 200 Myrs (Fig.

9c

). One analysis of a zircon dated at 2957 ± 11 Ma return initial 176 Hf/ 177 Hf of 0.280829 and ℇHf = -2.2. This analysis departs from the near constant array preserved in older grains and argues for late crustal reworking.

  ages ranging from ca. 2214 Ma to 2081 Ma. On the probability density plot, the data may be grouped as follow: 1) two single ages at ca. 2214 Ma and 2201 Ma; 2) one age cluster from ca.

	2187 Ma to 2184 Ma (n = 3) with obtained Th/U values between 0.86 and 0.62 and giving a
	weighted mean age of 2186 ± 3 Ma (MSWD = 0.53); 3) two single ages at ca. 2165 Ma and
	2157 Ma; 4) one age cluster from ca. 2140 Ma to 2131 Ma (n = 7) with Th/U comprised between
	1.13 and 0.34 and giving a weighted mean age of 2136 ± 3 Ma (MSWD = 1.07); 5) a sub-
	continuous record of ages from ca. 2123 Ma to 2090 Ma (n = 77) with Th/U comprised between
	2.49 and 0.24 showing a peak at ca. 2109 Ma; 6) a single zircon dated at 2082 ± 4 Ma with

  with ages comparable to those found in this study.Both the metamorphic age of the migmatitic gneiss and magmatic emplacement of potassic granite suites are also very close to the youngest ages of detrital zircons from the Kounoukou micaschist and Grand-Béréby paragneiss. The two metasedimentary samples both returned Paleoproterozoic age clusters. The sample of garnet-cordierite-sillimanite migmatitic gneiss of Grand-Béréby (GDB8) provides zircon ages ranging from ca. 2670 Ma to 2060 Ma. Whereas this sample presents Archean detrital zircons dated at ca. 2670 Ma (n = 1) the remaining concordant zircons display an age spectrum ranging from ca. 2213 to 2060 Ma, which overlap the sequence of events encountered in the Baoule-Mossi domain. It is also noteworthy that the youngest grain dated in this sample yields an age of 2069 ± 4 Ma. The other metasediment analysed in this study (garnet-staurolite-bearing micaschist of Kounoukou, KOU7), returned a comparable detrital zircon age spectrum ranging from ca. 2214 to 2082 Ma. Two hypotheses are possible to interpret the youngest ages: it could be either a maximum age for deposition of the sediment or the age of metamorphism of the sedimentary protolith. If these ages represent deposition ages, it suggests that the time lapse between sediment deposition and metamorphism during the Eburnean orogeny was very short. Alternatively, if these young ages are interpreted as metamorphic, the deposition age would then be ca. 2100 Ma, taking into account the main age peak at ca. 2109 Ma for KOU7. This hypothesis allows for a longer, and more realistic, time lapse between the deposition and metamorphism and is consistent with the time lag (ca.

ACKNOWLEDGEMENTS

This project is part of a PhD study of A.Y.K. funded by the T2GEM project (Geophysical and Geochemical Technologies for Mineral Exploration). We wish to gratefully acknowledge AMIRA International and the industry sponsors, for their support of the WAXI project (P934B).

We are also appreciative of the contribution of the various geological surveys department of mines in West Africa as sponsors in kind of WAXI. The authors acknowledge the French National Research Institute for Sustainable Development (IRD, LMI MINERWA Laboratory for Responsible Mining in West Africa) for funding a part of this research project. The authors wish to thank Brad McDonald (Curtin University) for technical assistance during analysis.

GeoHistory Facility instruments were funded via an Australian Geophysical Observing System grant provided to AuScope Pty Ltd. by the AQ44 Australian Education Investment Fund program. The NPII multi-collector and laser ablation system at UWA were obtained via funding from the Australian Research Council LIEF program (LE150100013). NT would like to acknowledge the Hammond and Nisbet trust for its support. The authors gratefully acknowledge two anonymous reviewers and Bernard Bingen for their constructive reviews. We also thank Chris Fisher and Oscar Laurent for their insights into the isotopic geochemistry which greatly helped improve the quality this manuscript.