Lydéric France

Gilles Chazot

Jacques Kornprobst

Luigi Dallai

Riccardo Vannucci

Michel Grégoire

Hervé Bertrand

Pierre Boivin

Michel Gregoire

Mantle refertilization and magmatism in old orogenic regions: The role of late-orogenic pyroxenites

Keywords: pyroxenite, mantle, cumulate, xenolith, metamorphic petrology, garnet, oxygen isotopes, eclogite, sapphirine, P-T conditions, Morocco, Jordan, Cameroon, French Massif-Central

Introduction

The shallowest part of the Earth's upper mantle is made primarily of peridotite, with spinel lherzolite and harzburgite being the most abundant lithologies. Pyroxenites and eclogites represent less than two percent of the upper mantle according to estimations based on isotopic considerations [START_REF] Pertermann | Partial melting experiments on a MORB-like pyroxenite between 2 and 3 GPa: constraints on the presence of pyroxenite in basalt source regions from solidus location and melting rate[END_REF], or up to five percent considering estimations made in orogenic peridotite massifs (e.g., [START_REF] Kornprobst | Le massif ultramafique des Beni Bouchera (Rif interne, Maroc): Etude des péridotites de haute temperature et de haute pression et des pyroxenolites, à grenat ou sans grenat, qui leur sont associées[END_REF][START_REF] Pearson | Geochemical Constraints on the petrogenesis of the diamond facies pyroxénites from the Beni Bousera peridotite massif, north Morocco[END_REF].

Although they represent only a small volume of the upper mantle, pyroxenites and eclogites provide important information about dynamic processes occurring since the formation of the Earth, and about crustal recycling and melt circulation through the mantle (e.g., [START_REF] Downes | Origin and significance of spinel and garnet pyroxenites in the shallow lithospheric mantle: Ultramafic massifs in orogenic belts in Western Europe and NW Africa[END_REF]Gonzaga et al., 2010a). Due to their fertile composition and low solidus temperature compared to the host mantle peridotites, pyroxenites are quite relevant during mantle partial melting and basaltic magma genesis [START_REF] Hirschmann | A possible role for garnet pyroxenites in the origin of the 'garnet signature' in MORB[END_REF][START_REF] Lambart | An experimental study of pyroxenite partial melts at 1 and 1.5 GPa: Implications for the major-element composition of Mid-Ocean Ridge Basalts[END_REF].

Their role in basalt genesis has indeed been inferred in oceanic and continental settings (e.g., [START_REF] Sobolev | An olivine-free mantle source of Hawaiian shield basalts[END_REF][START_REF] Heinonen | Mixed pyroxenite-peridotite sources for mafic and ultramafic dikes from the Antarctic segment of the Karoo continental flood basalt province[END_REF].

The origin of pyroxenites (as well as eclogites) found in mantle bodies or in mantle xenoliths is highly debated. They can represent dehydrated or residual and partially molten crustal lithologies recycled into the upper mantle through subduction zones (e.g., [START_REF] Allègre | Implications of a two-component marble-cake mantle[END_REF][START_REF] Viljoen | Contrasting Group I and Group II eclogite xenoliths petrogenesis: Petrological, trace element and isotopic evidence from eclogite, garnet-websterite and alkremite xenoliths in the Kaalvallei kimberlite, South Africa[END_REF]Gonzaga et al., 2010a;[START_REF] Montanini | Garnet clinopyroxenite layers from the mantle sequences of the Northern Apennine ophiolite (Italy): Evidence for recycling of crustal material[END_REF]. Such mantle heterogeneities usually display a greater variability in chemical and isotopic compositions compared to peridotitic mantle (e.g., Gonzaga et al., 2010a, b). Pyroxenites can also represent high-pressure cumulates fractionated from basaltic magmas circulating through the upper mantle [START_REF] O'hara | Formation and fractionation of basic magmas at high pressure[END_REF][START_REF] Viljoen | Contrasting Group I and Group II eclogite xenoliths petrogenesis: Petrological, trace element and isotopic evidence from eclogite, garnet-websterite and alkremite xenoliths in the Kaalvallei kimberlite, South Africa[END_REF][START_REF] Downes | Origin and significance of spinel and garnet pyroxenites in the shallow lithospheric mantle: Ultramafic massifs in orogenic belts in Western Europe and NW Africa[END_REF]Gonzaga et al., 2010a;[START_REF] Perinelli | Thermal evolution of the lithosphere in a rift environment as inferred from the geochemistry of mantle cumulates, Northern Victoria Land, Antarctica[END_REF], creating a veined mantle below ancient magmatic provinces.

Alternatively, this veined mantle has been interpreted as representing a lithospheric Garnet Pyroxenites in Old Orogenic Regions refertilization stage resulting from olivine-melt consuming and clinopyroxene-orthopyroxene forming reactions (e.g., [START_REF] Bodinier | Origin of Pyroxenite-Peridotite Veined Mantle by Refertilization Reactions: Evidence from the Ronda Peridotite (Southern Spain)[END_REF].

The terminology in use (eclogite versus garnet pyroxenite) is mainly governed by the origin of these rocks. In their review on eclogites and garnet pyroxenites, Gonzaga et al. (2010a) related garnet pyroxenites to high-pressure mantle fractionation processes, and eclogites to recycling of crustal protoliths. Historically, eclogites have been defined as rocks containing pyropegarnet and omphacitic-clinopyroxenes [START_REF] Haüy | Traité de minéralogie[END_REF]. Moreover, eclogites differ from garnet pyroxenites in that they are more common in cratonic xenolith suites and have a higher jadeite component in clinopyroxenes [START_REF] Pearson | Mantle samples included in volcanic rocks: xenoliths and diamonds[END_REF]. Despite these differences, multidisciplinary studies are still necessary to decipher the origin of a given sample, and giving an a priori name is therefore hazardous. Hereafter, we will use the petrological term garnet pyroxenite (garnet when more than 10% garnet is present, and pyroxenite when olivine / [olivine+pyroxenes] < 40%, following the Streckeisen classification; [START_REF] Streckeisen | To each plutonic rock its proper name[END_REF].

The mineral assemblages developed in pyroxenites in response to changes in pressure and temperature conditions are of great help in reconstructing the evolutionary stages they underwent in the appropriate geodynamic setting (e.g., [START_REF] Montanini | Exhumation history of a garnet pyroxenite-bearing mantle section from a continent-ocean transition (Northern Apennine ophiolites, Italy)[END_REF], whereas their chemical and isotopic compositions can be used to decipher their origin and evaluate their potential implication in magma genesis. The absence of modal olivine in mantle pyroxenites is associated with the presence of garnet under spinel lherzolite stability conditions [START_REF] Kornprobst | Le massif ultramafique des Beni Bouchera (Rif interne, Maroc): Etude des péridotites de haute temperature et de haute pression et des pyroxenolites, à grenat ou sans grenat, qui leur sont associées[END_REF]; this leads to the existence of two subfacies, namely the Seiland at lower and the Ariegite at higher pressure conditions [START_REF] O'hara | Mineral facies in ultrabasic rocks[END_REF]. In these two subfacies, the Albearing phases consist of plagioclase and/or spinel, and spinel and/or garnet, respectively. These two subfacies subdivide the spinel lherzolite domain and allow us to determine more precisely the pressure-temperature-time (P-T-t) evolution of the lithosphere than with peridotitic samples.

Garnet Pyroxenites in Old Orogenic Regions

We present here a petrological and geochemical study of 16 mantle garnet pyroxenite xenoliths (from Morocco, Jordan, Cameroon and France) that represent the rare material available for petro-geochemical studies. The aims of this study are: (i) to evaluate the similarities and/or differences between pyroxenite samples from the different regions; (ii) to constrain the origin of the studied pyroxenites; (iii) to constrain the P-T-t evolution of the studied pyroxenites within the mantle; (iv) to evaluate the relations between the determined P-T-t paths and the geodynamic history of the regional lithosphere; and (v) to discuss the influence of these mantle heterogeneities on the subsequent evolution of the lithosphere.

Regional settings and sampling localities

In order to compare the geodynamic evolution and chemical and isotopic composition of pyroxenites, we studied samples from four localities, each with different geodynamic histories: the French Massif Central (Europe), Morocco and Cameroon (Africa) and Jordan (on the Arabian plate; Fig. 1).

French Massif Central (FMC): The Massif Central (Fig. 1a) represents one of the biggest parts of the Variscan belt of Western Europe. Alkaline volcanism developed throughout Cenozoic times, with the last manifestation occurring in the Chaîne des Puys 6,900 ± 110 yr. cal. as the lake Pavin maar [START_REF] Juvigné | A comprehensive pollen and tephra-based chronostratigraphic model for the Late-glacial and Holocene period in the French Massif-Central[END_REF]. The origin of this volcanism is still debated, and is either attributed to the presence of a thermal anomaly related to a mantle plume (e.g., [START_REF] Granet | Imaging a mantle plume beneath the French Massif Central[END_REF] or to asthenospheric upwelling related to the nearby Alpine orogeny [START_REF] Merle | The formation of the West European rift: a new model as exemplified by the Massif Central area[END_REF].

Mantle xenoliths are present in several locations of the FMC. Two distinct domains, probably inherited from Hercynian times, are recognized N and S of an E-W line located ~45°30'N [START_REF] Lenoir | Contrasting domains beneath the Massif Central (France) revealed by geochemistry of peridotites xenoliths[END_REF]. Both domains have been variously depleted through melting ~360 Ma ago, and have been enriched by metasomatic fluids (carbonatitic to the North, and rather Garnet Pyroxenites in Old Orogenic Regions related to silicate-melts to the South; [START_REF] Wittig | U-Th-Pb and Lu-Hf isotopic constraints on the evolution of subcontinental lithospheric mantle, French Massif Central[END_REF] likely related to the Cenozoic plume [START_REF] Zangana | Relationship between deformation, equilibration temperatures, REE and radiogenic isotopes in mantle xenoliths (Ray Pic, Massif Central, France): an example of plume-lithosphere interaction?[END_REF][START_REF] Wittig | U-Th-Pb and Lu-Hf isotopic constraints on the evolution of subcontinental lithospheric mantle, French Massif Central[END_REF].

Three of the studied samples come from the Devès volcanic field (S domain; LN-78 and LP-27 from Le Marais de Limagne, and SD-53 from Saint-Didier d'Allier), a basaltic plateau emplaced between 2.7 and 0.6 Ma [START_REF] Nehlig | Les volcans du Massif Central[END_REF]. Teleseismic tomography studies indicate that the thermal anomaly in the mantle between 100 and 140 km below the Devès area is the largest of the FMC [START_REF] Sobolev | Upper mantle temperatures from teleseismic tomography of French Massif Central including effects of composition, mineral reactions, anharmonicity, anelasticity and partial melt[END_REF]. One sample comes from Le Pouget, near Montpellier; this locality does not belong to the FMC but, instead, to the 'pyreneo-corsosarde' Alpine belt. As the basement of this orogenic segment is also made of old Hercynian lithosphere, the Le Pouget sample will be described together with the FMC samples. This last sample has been briefly studied in previous works [START_REF] Babkine | Découverte d'une enclave d'ariégite à grenat dans l'absarokite du Pouget (Herault)[END_REF][START_REF] Fabriès | Petrology and thermal history of highly deformed mantle xenoliths from the Montferrier basanites, Languedoc, southern France: A comparison with Ultramafic Complexes from the north Pyrenean Zone[END_REF].

Cameroon (Fig. 1b): The oldest Cameroon terrains were structured during Eburnean times some 2.1 Ga ago and were reworked during the Panafrican orogeny [START_REF] Castaing | Palaeogeographical reconstructions of the Pan-African/Brasiliano orogen: closure of an oceanic domain or intracontinental convergence between major blocks?[END_REF].

Many granite bodies were emplaced around 520 Ma (Lassere et al., 1981).

Pyroxenites were sampled in the Youkou maar, in the Adamaoua volcanic plateau [START_REF] Temdjim | Contribution à la connaissance du manteau supérieur du Cameroun au travers de l'étude des[END_REF]. This maar belongs to the Cameroon Volcanic Line (CVL; part of a still-active fault belt in West Africa), which is characterized by important Tertiary and Quaternary alkaline magmatism extending off-continent to several oceanic islands. Volcanism in this area started around 60 Ma ago [START_REF] Cantagrel | Le magmatisme alcalin de la Ligne du Cameroun au Tertiaire inférieur, données géochronologiques K[END_REF] and is still active today. Mantle xenoliths (spinel lherzolites being the most common) are present in volcanic rocks from both oceanic and continental parts of the CVL. Several studies have emphasized a partial melting event probably related to late Proterozoic crust formation [START_REF] Lee | Melt enrichment of shallow depleted mantle: A detailed petrological, trace element and isotopic study of mantle derived xenoliths and megacrysts from the Cameroon Line[END_REF]. In many places, the mantle rocks show evidence of interaction with enriched partial melts, probably related to the Mesozoic breakup of Pangaea and the emplacement of the St. Helena mantle plume [START_REF] Lee | Melt enrichment of shallow depleted mantle: A detailed petrological, trace element and isotopic study of mantle derived xenoliths and megacrysts from the Cameroon Line[END_REF][START_REF] Caldeira | Petrology of ultramafic nodules from São Tomé Island, Cameroon Volcanic Line (oceanic sector)[END_REF][START_REF] Temdjim | L'hétérogénéité du manteau supérieur à l'aplomb du volcan de Nyos (Cameroun) révélée par les enclaves ultrabasiques[END_REF].

Garnet Pyroxenites in Old Orogenic Regions

Morocco (Fig. 1c): The middle Atlas area of Morocco is part of the Atlas Mountain range of North Africa and was mainly structured during the Panafrican orogeny, lasting roughly from 700 to 530 Ma [START_REF] Gasquet | Contribution to a geodynamic reconstruction of the Anti-Atlas (Morocco) during Pan-African times with the emphasis on inversion tectonics and metallogenic activity at the Precambrian-Cambrian transition[END_REF]. The orogenic period was followed by the formation of large Paleozoic sedimentary basins that were strongly folded during late Carboniferous-Permian compression [START_REF] Pique | Moroccan Hercynides; a synopsis; the Paleozoic sedimentary and tectonic evolution at the northern margin of West Africa[END_REF]. Cenozoic volcanism started before 35 Ma; the last eruptions are probably not older than 0.5 Ma [START_REF] Pyroxenites | Petrology and K-Ar chronology of the Neogene-Quaternary Middle Atlas basaltic province Morocco[END_REF] and are tentatively linked to a hot line spreading from the Siroua to Oujda (e.g., El Azzouzi et al., 2010).

Mantle xenoliths are present in volcanic rocks from the middle Atlas, and show a wide range of lithological and chemical heterogeneity. As in Cameroon, an older melting event is recorded by the chemistry of clinopyroxene [START_REF] Raffone | Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe-and Mg-rich Wehrlites[END_REF][START_REF] Wittig | A major element, PGE and Re-Os isotope study of Middle Atlas (Morocco) peridotite xenoliths: Evidence for coupled introduction of metasomatic sulphides and clinopyroxene[END_REF]. In most samples, this event has been overprinted by a widespread modal metasomatism [START_REF] Pezzali | Analogues of exhumed pyroxenite layers in the Alboran domain sampled as xenoliths by Middle Atlas Cenozoic volcanism[END_REF]. This metasomatic episode is probably very young (less than 200 Ma) and involves the percolation of alkaline melts with HIMU affinity as well as carbonatitic fluids [START_REF] Raffone | Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe-and Mg-rich Wehrlites[END_REF][START_REF] Natali | Carbonated alkali-silicate metasomatism in the North Africa lithosphere: Evidence from Middle Atlas spinel-lherzolites, Morocco[END_REF][START_REF] Pezzali | Analogues of exhumed pyroxenite layers in the Alboran domain sampled as xenoliths by Middle Atlas Cenozoic volcanism[END_REF].

The Morocco samples come from the Bou-Ibalratene basaltic maar belonging to a volcanic group of nearly 100 monogenic edifices oriented about N170°E, and located South of Azrou in the middle Atlas.

Jordan (Fig. 1d): Jordan is located in the northern part of the Arabian-Nubian shield and was affected by important metamorphism and magmatism during the Panafrican orogeny from 640 to 540 Ma ago [START_REF] Stein | From plume head to continental lithosphere in the Arabian-Nubian shield[END_REF]. Large alkaline volcanic fields named 'Harrats' are present all along the Arabian plate from Yemen in the South to Jordan and Syria in the North.

They are related to the Red Sea and Jordan rifts and were emplaced during Tertiary and Quaternary times [START_REF] Bertrand | Implications of widespread HIMU volcanism on the Arabian Plate for the composition of the Afar mantle plume and lithoshere[END_REF].

The Jordan samples come from three different maars belonging to the large, NW-SE trending, Harrat Ash Shaam that extends from SW Syria to the Northern part of Saudi Arabia. Studies concerning Harrat Ash Shaam mantle xenoliths have shown that the mantle in this region was affected by partial melting and refertilization events between 870 and 620 Ma ago. These processes are related to the formation of juvenile crust in a continental arc system [START_REF] Krienitz | The evolution of the Arabian lower crust and lithospheric mantle -Geochemical constraints from southern Syrian mafic and ultramafic xenoliths[END_REF].

Analytical techniques

This study is based on major and trace element and isotope analyses of whole rocks and mineral separates (separated under binocular microscope for their purity after crushing, sieving and washing). In-situ chemical analyses have been made on polished thin sections (30, 100 or 150 µm thick). Details on analytical techniques and settings are given in supplementary material.

Petrology

Petrography

The sample labels, rock types and modes of the studied samples, and the abbreviations used for minerals are presented in Table 1.

Pyroxenites from the FMC have recrystallized granoblastic textures with average grain size of 1 mm for the samples from the Devès volcanic province (LN-78, LP-27 and SD-53); grain size is smaller in the sample from Le Pouget (pyroxenes ~0.25 mm, Spl and Grt ~0.75 mm).

The prevailing mineral assemblage in all the samples is Cpx+Grt+Opx+Spl±Am. Grt is often located around green Spl and contains green Spl, Pl, Opx and Cpx inclusions that are surrounded by radial fractures (Fig. 2a-b). Those inclusions are remnants of a former paragenesis. In LN-78 larger Cpx grains (>2 mm) display Opx exsolutions (Fig. 2c). This sample is composite with an Am-free part and an Am-rich zone. In the three Devès samples, small grains (50 -100 µm) of Opx, Pl and brownish Spl are locally observed at the contact between Grt and Cpx (Fig. 2d). In all samples, Grt is surrounded by a thin (5 to 40 µm; Fig. 2b,d) brownish kelyphite rim made of Opx-Pl-Spl (proportions 64:23:13%, respectively, estimated using mineral compositions and the method of [START_REF] France | MetaRep, an extended CMAS 3D program to visualize mafic (CMAS, ACF-S, ACF-N) and politic (AFM-K, AFM-S, AKF-S) projections[END_REF].

Samples TAK-3 and TAK-4 from Morocco have a granular texture with an average grain size of 3 mm and show a penetrative foliation. The paragenesis is Grt+Opx+Cpx+Spl for TAK-3 and Grt+Cpx+Spl+Spr+Opx for TAK-4. In TAK-3, Grt occurs around the Spl demonstrating an earlier crystallization of Spl, whereas in TAK-4, the Grt-Spl association is observed only locally (Fig. 2e-f). In TAK-3 large Cpx grains (6 mm) contain Grt and Opx exsolutions, and some very thin (1-2 µm) Spl exsolutions are observed in other Cpx. In TAK-4, Spr is present as inclusions in Spl or Cpx, surrounding the Spl at the Grt contact (Fig. 2e-f), or as thin exsolutions in Cpx. In this same sample a peculiar inclusion is observed in a Cpx grain, containing a Spl+Spr+Pl+Opx assemblage (Fig. 2g). Both samples suffered extended Grt kelyphitization (~0.4 mm large in average).

Petrographically, the Cameroon samples can be divided in two groups. The first group (YK-01, YK-05 and YK-16) represents initial Cpx megacrysts (0.5-3cm) that exsolve Grt grains up to 500 µm wide (Fig. 2h-j). In YK-01 Cpx encloses Spl grains that are surrounded by abundant Grt (Fig. 2h). YK-05 megacrysts record a deformation stage and exsolve Opx (Fig. 2i-j). The second group (YK-03, YK-12, YK-13) is characterized by a polycrystalline Cpx+Opx+Grt+Spl assemblage (average grain size 3 mm). In these samples, Grt is either exsolved from Cpx, or localized around Cpx grains and concentrated at the Spl rim. In YK-13, Opx is also localized around Cpx grains and is probably exsolved. In this sample, some apatite is observed, locally included in Grt or Opx. Thin Am exsolutions (~20 µm wide) are also observed in some Cpx grains. In Cpx from all Cameroon samples, very thin (1-2 µm Garnet Pyroxenites in Old Orogenic Regions wide) Spl exsolutions are present; in samples YK-13 and YK-16, these can reach tens of µm and are locally surrounded by Grt exsolutions. Am is present in all the samples except YK-01.

A thin (≤ 20 µm) kelyphitization zone is present around Grt, and a melting zone (< 15 µm) is often observed at the contact between kelyphite and surrounding minerals. Later surface processes are documented by some carbonate veins that crosscut Grt kelyphite and melting zones.

The Jordan samples include Spl Grt pyroxenites (JO-7b and JO-7h) and Grt free orthopyroxenites (JO-10e and JO-12h); JO-12h is an Am-bearing olivine orthopyroxenite.

The average grain size in all samples is 1 mm (Fig. 2k). In JO-7b and JO-7h, Grt (~50 µm) is exsolved from pyroxene, around which it concentrates; some Grt also appears around green (in JO-7b, Fig. 2k) or brown (in JO-7h) Spl. In JO-7h some very thin (~2 µm) Spl exsolutions are observed in Cpx. In JO-10e orthopyroxenite, rutile is observed along two exsolution directions in Opx (Fig. 2l); moreover, this sample is diffusely permeated by dikelets and pockets of carbonate. In JO-7h, Opx is fractured and oxidized at its rim. In both JO-7b and JO-7h, Grt is kelyphitized (~40 µm wide) at the margins.

Major element mineral chemistry

Mineral compositions are very homogeneous in each studied sample, allowing us to use average compositions to compare the different samples (Table 2). Cpx and Opx are diopside and enstatite, respectively. Their compositions are broadly similar in the samples from the different provenances (Fig. 3a). In Cpx, wollastonite content is higher than 43%, ferrosilite content lower that 10%, and jadeite content varies from 4.7 to 12.5%, whereas in Opx wollastonite content is lower than 2%, ferrosilite content varies between 9 and 18%, and jadeite content is below 1%. TAK-4 Cpx are not stoichiometric; they are silica (Si/(Ca+Na+Mg+Fe)=1.04) and Ca (X Wo =0.51) enriched. Grt are pyrope (Fig. 3b), with compositions between 62 and 73% for the pyrope component (Mg) and between 11 and 24% for the almandine component (Fe) at a nearly constant grossular (Ca) content (~13%). Spl show a wide range of compositions. The Cr 2 O 3 vs. Al 2 O 3 anti-correlation (R²=0.96) is related to the Al-Cr substitution in Spl and shows a variation from 0 to 30% of the chromite component. For all the studied samples, the ratio Mg-component/Fe 2+ -component (spinel s.s./hercynite) is around 2, and #Cr varies from 1 to 12% in all samples except JO-12h, for which the value is 30.5% (with #Cr=Cr/(Cr+Al) in molar proportions). For the samples displaying two Spl generations (LN-78, LP-27 and SD-53), the brown ones (second generation) are poorer in chromite component than the primary green ones. Pl compositions are variable, ranging from andesine in FMC samples (with anorthite content varying from 35 to 47 mol%), to bytownite in TAK-4 (Morocco; An 84 ). Analyzed amphiboles are magnesiohastingsites in LN-78, YK-05 and YK-13, pargasites in YK-03 and ferro-edenite in JO-12h. Olivine is Fo 89 in JO-12h.

Mineral trace element compositions

Trace element compositions of minerals have been obtained for Cpx and Grt in all samples, and for Am, Pl, and Opx when these minerals were large enough (Table 3). Cpx trace element composition is variable in the different samples, and sometimes within a single sample. In FMC samples (Fig. 4a), the Cpx show variable light-rare earth elements (LREE) contents, ranging from strongly depleted (in Le Pouget sample) to slightly enriched compared to the medium-REE (MREE). They are also depleted in heavy-REE (HREE), reflecting their chemical equilibrium with Grt (see section 8.1.2 "Cpx/Opx and Cpx/Grt partition coefficients"). In sample LN78, some Cpx located close to Am grains are highly enriched in LREE, less HREE depleted than other Cpx, and have REE content similar to associated Am grains. In the two Morocco samples (Fig. 4a), the Cpx have REE normalized contents that Garnet Pyroxenites in Old Orogenic Regions decrease from the LREE to the HREE region. In TAK-4 the decrease from the LREE to the HREE is more pronounced than in TAK-3 and slight positive Eu and Sr anomalies are present (Fig. 4b). Similar to their analogues from FMC, Cpx in the Cameroon samples are all HREE depleted (Fig. 4c), in agreement with the presence of Grt. Their LREE composition is variable and ranges from 0.6 to more than 10 times the chondrite value. Grt-bearing samples from Jordan show two types of Cpx compositions (Fig. 4c); Cpx grains in contact with Grt are strongly depleted in HREE relative to MREE, whereas those far from Grt are only slightly depleted. Their LREE content is also variable, from largely depleted in JO-7b to slightly enriched in JO-7h. In Grt-free samples, Cpx possess higher REE abundances and are LREE enriched. In all these samples, Cpx have very low Nb, Ta and often Zr and Hf contents (Fig. 4b,d). All the analyzed Grt grains show typical REE patterns, highly enriched in HREE (up to 100x chondrite in TAK-3 from Morocco) in comparison to largely depleted LREE contents (Fig. 4e). Some Grt display relatively flat patterns from MREE to HREE, reflecting the low HREE contents of the whole rock. Grt is strongly enriched in U (Fig. 4f). Pl in FMC samples is LREE enriched and shows strong Eu, Sr and Ba positive anomalies (Table 3).

Whole rock major and trace element compositions

Whole rock major element compositions are summarized in Table 4 andFigure 5. Mg# (where Mg# = Mg/(Mg+Fe) in molar proportions) varies from 79.8 in SD-54 (FMC) to 89.3 in JO-7h (Jordan; Table 4). SiO 2 content ranges from 42.6 to 54.7 wt%; the lowest values are found in the two samples from Morocco which are thus classified as ultramafic rocks while all other samples are mafic rocks (Le [START_REF] Bas | The IUGS systematics of igneous rocks[END_REF]. MgO content varies from 15.5 wt% in LP-27 (FMC) to 33.1 wt% in JO-12h (Jordan). Al 2 O 3 content ranges from 3.2 wt% in JO-10e (Jordan) to 22.5 wt% in TAK-4 (Morocco). CaO content varies from 1.7 wt% in JO-12h (Jordan) to 16.4 wt% in Le Pouget sample (FMC). FeO t (all iron expressed as FeO) content varies from 4.6 wt% in JO-7h (Jordan) to 8.1 wt% in JO-10e (Jordan). Na 2 O content ranges from 0.04 wt% in JO-12h (Jordan) to 1.41 wt% in . In all the oxideoxide composition plots, whole rock compositions plot between the main bearing minerals, namely Cpx, Opx, Spl, and Grt. Some samples, especially those from Morocco, are furthermore slightly shifted toward the Spl and/or Spr composition. MgO is correlated with SiO 2 , and anticorrelated with CaO and Al 2 O 3 . The average composition of primitive MORB and alkaline melts are added in Figure 5, and are considered as possible proxies of a prospective trapped melt in mantle domains.

Whole rock trace element concentrations are summarized in Table 4 and Figure 6. Whole rock REE content for FMC pyroxenites show typical spoon-shaped patterns with high HREE content, depletion in MREE and enrichment in LREE (Fig. 6a). The two different parts of LN-78 have parallel REE patterns, the Am-rich part being more LREE enriched; Le Pouget sample possesses similar MREE and HREE composition, but is largely depleted in LREE, with La lower than 0.1x chondrite, in agreement with its strongly LREE depleted Cpx (Fig. 4a). The two samples from Morocco have contrasting REE compositions; TAK-3 pyroxenite shows a pattern similar to the FMC pyroxenites, whereas the Spr-bearing TAK-4 sample has a very low HREE content (< 3x chondrite) coupled with a marked LREE enrichment (La > 35x chondrite), and a small positive Eu anomaly associated with a positive Sr anomaly. Similar to the FMC samples, two types of REE patterns are displayed by the Cameroon pyroxenites (Fig. 6c); they all have low HREE content, and most of the samples are LREE depleted. Only two samples (YK-13 and YK-16) show LREE enrichment. The pyroxenites from Jordan also have contrasted REE patterns (Fig. 6e). Three samples are LREE enriched, with (La/Yb) n values ranging from 2.5 to 7 and quite variable HREE compositions, while sample JO-7b is LREE depleted.

Garnet Pyroxenites in Old Orogenic Regions

In trace element spider diagrams (Fig. 6b,d,f), all samples present large negative Rb and Nb anomalies, associated with negative Zr anomalies (except for TAK-3 that displays a slight positive anomaly). Most of the samples also display a positive Sr anomaly; only JO-10e (Jordan) displays a negative Sr anomaly.

Isotopic data

Sr-Nd isotope data have been obtained on separated Cpx from four samples from Jordan, three from Cameroon, and two from Morocco (Table 5; not enough material was available for other samples). 87 Sr/ 86 Sr values are homogeneous and range from 0.702661 to 0.703375 (Fig. 7); in contrast, 143 Nd/ 144 Nd values are more variable and range between 0.512774 and 0.513433.

Both the lowest and highest values are observed in Jordan samples. All the samples, except JO-7b and TAK-3, plot below the mantle array; most values are close to the HIMU component [START_REF] Zindler | Chemical geodynamics[END_REF]. 50 analyses of oxygen isotopic ratios have been obtained on Cpx, Opx, Grt and Spl separates (Table 5). Most of the values fall within the mantle range for peridotites [START_REF] Ionov | Oxygen isotope composition of garnet and spinel peridotites in the continental mantle: Evidence from the Vitim xenolith suite, southern Siberia[END_REF]Mattey et al., 1994a;[START_REF] Chazot | Oxygen isotopic composition of hydrous and anhydrous mantle peridotites[END_REF][START_REF] Zhang | Recent fluid processes in the Kaapvaal Craton, South Africa: coupled oxygen isotope and trace element disequilibrium in polymict peridotites[END_REF], with  18 O ranging from 4.82 to 5.72‰ for Cpx, from 4.94 to 6.12‰ for Opx, from 5.15 to 5.97‰ for Grt, and from 4.33 to 4.97‰ for Spl (Fig. 8). Fractionation between Grt and Cpx is positive and close to 0.3‰ with the exception of three samples from Cameroon having slightly negative fractionation values (Fig. S1a). Fractionation between Opx and Cpx is also positive (except for two samples, Fig. S1b), and in the range of values observed in mantle lherzolites from Yemen [START_REF] Chazot | Oxygen isotopic composition of hydrous and anhydrous mantle peridotites[END_REF].

Discussion

Garnet Pyroxenites in Old Orogenic Regions

The various petrographical and geochemical data presented are discussed hereafter to determine the last equilibration stage conditions (T, fO 2 , section 8.1) of the studied Grt pyroxenites, and to track their origin (recycled or not?, section 8.2) and the metasomatic reactions they subsequently suffered (section 8.3). Pyroxenite pressure-temperature variations through subsolidus evolution are reconstructed for each sample (section 8.4), and the apparent inter-and intra-region variability (petrographical and geochemical) are discussed in section 8.5. Finally we present our hypothesis in a geodynamic framework to discuss implications in terms of mantle refertilization (section 8.6).

Last equilibration stage conditions

Thermometry and oxybarometry

Equilibrium temperature (T) estimates are presented in Table 1. Opx-Cpx equilibrium T of Grt-bearing peridotites and pyroxenites are best estimated using the [START_REF] Taylor | An experimental test of some geothermometer and geobarometer formulations for upper mantle peridotites with application to the thermobarometry of fertile lherzolites and garnet websterite[END_REF] geothermometer [START_REF] Wu | Reply to comment on "The applicability of garnet-orthopyroxene geobarometry in mantle xenoliths" by Paolo Nimis and Herman Grütter[END_REF], and are as follows: 730°C and 930-1080°C (Le Pouget and other FMC samples, respectively), 910°C (TAK-3, Morocco), 780-810°C (Jordan), and 900-980°C (Cameroon). Equilibrium T cannot be estimated for TAK-4 since it contains aluminous diopside. For comparison, Opx-Grt equilibrium T, calculated using the [START_REF] Nimis | Internally consistent geothermometers for garnet peridotites and pyroxenites[END_REF] geothermometer, are as follows: 715-1020°C (FMC), 890°C (TAK-3, Morocco), 720-760°C (Jordan), and 870-980°C (Cameroon). In general, equilibrium T calculated with both geothermometers are consistent. Because 2+ cations diffuse faster than 3+ cations, T calculated using major element based thermometers are likely to be indicative of late stage equilibration T, whereas REE-in-two-pyroxene thermometers are expected to be indicative of sub-magmatic T (e.g., [START_REF] Liang | A REE-in-two-pyroxene thermometer for mafic and ultramafic rocks[END_REF]. Valid results have been obtained using the [START_REF] Liang | A REE-in-two-pyroxene thermometer for mafic and ultramafic rocks[END_REF] model for two samples from the present study: LN-78: 1376 ±126 °C, and LP-27: 1194 ±69 °C; those equilibrium T are consistent with the record of an early magmatic stage.

Redox conditions of mantle domains are usually estimated using oxybarometers that necessitate olivine bearing-rocks (e.g., [START_REF] Goncharov | Redox state of deep off-craton lithospheric mantle: new data from garnet and spinel peridotites from Vitim, southern Siberia[END_REF], and are thus not appropriate for the olivine-free pyroxenites studied here. Fe 3+ concentrations in Cpx, Opx, and Grt have been estimated using stoichiometric criteria following the classical approach of [START_REF] Droop | A general equation for estimating Fe 3+ concentrations in ferromagnesian silicates and oxides from microprobe analyses, using stoichiometric criteria[END_REF]; corresponding Fe 3+ /ΣFe values are reported in Table S1 and Fig. 9. Although such calculation results should be taken with caution, good correlations exist between (Fe 3+ /ΣFe) Opx and (Fe 3+ /ΣFe) Cpx (R 2 =0.69), between (Fe 3+ /ΣFe) Grt and (Fe 3+ /ΣFe) Opx (R 2 =0.85), and between (Fe 3+ /ΣFe) Grt and (Fe 3+ /ΣFe) Cpx (R 2 =0.71; Fig. 9). Those good correlations strongly support the validity of the stoichiometric calculations for the present study: (Fe 3+ /ΣFe) Cpx ranges from 0 to 0.6, (Fe 3+ /ΣFe) Opx from 0 to 0.22, and (Fe 3+ /ΣFe) Grt from 0 to 0.21. (Fe 3+ /ΣFe) Melt was calculated using (Fe 3+ /ΣFe) Cpx values and the approach formulated in France et al. (2010). Rough estimates for ΔFMQ (Fayalite-Magnetite-Quartz oxygen fugacity buffer) were obtained using the correlation between ΔFMQ and (Fe 3+ /ΣFe) Grt presented by [START_REF] Goncharov | Redox state of deep off-craton lithospheric mantle: new data from garnet and spinel peridotites from Vitim, southern Siberia[END_REF]. (Fe 3+ /ΣFe) Melt is plotted against ∆FMQ in Fig. 9.

More generally, the FMC samples appear to be the most reduced pyroxenites with (Fe 3+ /ΣFe) Melt ranging from 0.4 to 0.6; Jordan pyroxenites are slightly less reduced with an average (Fe 3+ /ΣFe) Melt of 0.6; the average (Fe 3+ /ΣFe) Melt for Morocco samples is 0.66; and Cameroon samples are the most oxidized samples studied herein with (Fe 3+ /ΣFe) Melt ranging from 0.56 to 0.83 for an average value of 0.73 (Fig. 9).

Cpx/Opx and Cpx/Grt partition coefficients

The major element compositional homogeneity of all the minerals among the studied samples, and the presence in most of the samples of well-developed exsolution lamellae indicate that Garnet Pyroxenites in Old Orogenic Regions (at least partial) intra-sample equilibrium was achieved; this is supported by the typical mantle T calculated from the chemical composition of Cpx, Opx and Grt (Table 1). Oxygen isotope data also show that no large disequilibrium exists between minerals in the studied pyroxenites. This chemical equilibrium among minerals was also tested by trace element partition coefficient calculations between Cpx and Opx, and between Cpx and Grt in the different samples (Fig. 10). The calculated K D(Cpx-Grt) values are in the range of values published by [START_REF] Viljoen | Contrasting Group I and Group II eclogite xenoliths petrogenesis: Petrological, trace element and isotopic evidence from eclogite, garnet-websterite and alkremite xenoliths in the Kaalvallei kimberlite, South Africa[END_REF] for group II eclogites from South Africa, interpreted as crystallization products of small-volume melts in the lithospheric mantle. Our values are also very similar to those obtained in a Cpx megacryst aggregate crystallized from a MORB type magma in the lithospheric mantle of China [START_REF] Huang | Exsolution lamellae in a clinopyroxene megacryst aggregate from Cenozoic basalt, Leizhou Peninsula, South China: petrography and chemical evolution[END_REF], and to K D(Cpx-Grt) determined experimentally at pressures varying from 2 to 3 GPa [START_REF] Johnson | Experimental cpx/and garnet/melt partitioning of REE and other trace elements at high pressures: petrogenetic implications[END_REF]. K D(Cpx-Grt) are dependent on the major element phase compositions (e.g., [START_REF] Harte | Partitioning of trace elements between clinopyroxene and garnet: data from mantle eclogites[END_REF]; calculations accounting for mineral compositions align closely with K D(Cpx-Grt) values obtained in the present study (Fig. 10). These results support that Cpx and Grt have attained chemical equilibrium at mantle conditions in all the studied samples before their fast transport to the surface. K D(Cpx-Opx) values are compared to results obtained by [START_REF] Raffone | Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe-and Mg-rich Wehrlites[END_REF] on lherzolites and harzburgites from Morocco (Fig. 10). Although a strong variability is observed in our data (due to large errors on the trace element concentrations of Opx that are strongly depleted in trace elements), K D(Cpx-Opx) are in the range of mantle values determined by [START_REF] Raffone | Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe-and Mg-rich Wehrlites[END_REF].

Pyroxenite origin as mantle cumulates

It is still a matter of debate whether pyroxenite xenoliths brought to the surface by volcanic processes represent metamorphically transformed crustal rocks (of either continental or oceanic origin) or are the final products of melt circulation, crystallization and evolution in the Garnet Pyroxenites in Old Orogenic Regions mantle. Here we use highly detailed petrological observations and major and trace element compositions, coupled with stable and radiogenic isotopic compositions to decipher their origin.

Whole rock compositions as a proxy of initial cumulative assemblages

Whole rock major element compositions define relatively good correlations for SiO 2 , CaO and Al 2 O 3 versus MgO content (Fig. 5), and Al 2 O 3 and SiO 2 are also well correlated. The pyroxenites studied here show an increase in SiO 2 content correlated to an increase in MgO (Fig. 11), which is in contrast to classic liquid lines of descent that highlight melt differentiation processes (e.g., for MORB, calc-alkaline, or alkaline rocks) characterized by a decrease in MgO when SiO 2 increases. High concentrations of highly compatible elements such as Ni can be used to identify cumulative rocks, in which their concentration is by definition higher than in the corresponding equilibrium melts. The Ni content of the studied pyroxenites (~300-900 ppm) is much higher than most primitive MORBs (~300 ppm, and decreasing with differentiation; Fig. 11), indicating that they cannot represent liquids, but rather are cumulates (either s.s. cumulates or cumulates resulting from percolative fractional crystallization). At this stage of discussion, their origin as crustal or mantle cumulates cannot be deciphered.

Since the studied pyroxenites represent cumulative rocks, their whole rock composition (major and trace elements) is indicative of the modal proportion of the initial cumulative assemblage; for example, the high Ni content attests to the presence of Spl among the cumulative minerals. We now present evidence supporting the assemblages that are reported in Table 1. The presence of magmatic Grt in four samples (FMC samples, and TAK-3 from Morocco; Fig. 6) is confirmed by the whole rock enrichment in HREE relative to MREE. The major element composition and Ni content of those samples also indicate that Cpx-Opx-Spl Garnet Pyroxenites in Old Orogenic Regions were part of the initial cumulative assemblage (red dotted samples in Fig. 5). Among the studied pyroxenites, 3 samples from Cameroon (YK-01, YK-03, YK-12) display small but significant positive Eu anomalies (Fig. 6), classically indicating magmatic Pl. However, similar anomalies have been reported in spinel-bearing peridotitic Cameroon mantle, and attributed to regional metasomatism (e.g., [START_REF] Temdjim | L'hétérogénéité du manteau supérieur à l'aplomb du volcan de Nyos (Cameroun) révélée par les enclaves ultrabasiques[END_REF]. This signature being regional, and in the absence of other evidence, we follow their interpretation and infer that Pl was not part of the initial cumulative assemblage in Cameroon samples. Only TAK-4 from Morocco displays coupled positive Eu and Sr anomalies (Fig. 6) that have not been reported for peridotitic samples from this area, and should be attributed to the presence of Pl in the initial cumulative assemblage. In this sample, the major element and Ni concentrations point to the additional presence of Cpx and Spl in the initial cumulative assemblage (Fig. 5). Major elements and Ni concentrations of Cameroon samples demonstrate that Cpx-Sp (±Opx) were part of the initial cumulative assemblage in all samples (Fig. 5), consistent with petrographic observations. Petrographic relations also suggest that apatite was present as a magmatic mineral in YK-13. According to petrography, major elements, and Ni contents, Opx was the main cumulative mineral in JO-10e and JO-12h, together with Ol-Spl-Cpx in JO-12h, and Spl-Cpx in JO-10e; two pyroxenes and Spl were present in the initial cumulative assemblages of JO-7b, and 7h (Fig. 5, Table 1).

In addition to the cumulative mineral record, [START_REF] Downes | Origin and significance of spinel and garnet pyroxenites in the shallow lithospheric mantle: Ultramafic massifs in orogenic belts in Western Europe and NW Africa[END_REF] invoked a trapped melt component to account for the whole rock major element compositions of orogenic pyroxenites interpreted to be mantle cumulates. In order to test this hypothesis, the compositions of relatively primitive mantle melts (represented by primitive MORBs and alkaline basalts) have been added to all graphs of Fig. 5. Only two samples (LP-27 from FMC, and YK-13 from Cameroon) seem to record a slight influence of trapped melt in their whole rock composition, as highlighted by their high Na 2 O contents. This hypothesis is consistent with the LREE Garnet Pyroxenites in Old Orogenic Regions enrichment of those samples; in addition YK-13 is the only sample to contain early magmatic apatite, also consistent with a possible trapped melt component.

The initial cumulative assemblages determined here will be used in section 8.4 to determine the in which mantle domain crystallization occurred. Finally the major and trace element whole rock compositions of the studied cumulative pyroxenites are only representative of the initial cumulative assemblage (nature of the phases and modal composition) and are thus not indicative of the composition of the parental melts that thus cannot be determined.

An alternative hypothesis to the cumulative origin of the studied pyroxenites is that Grtpyroxenites form as refractory residues after partial melting of eclogitic metagabbros (e.g., [START_REF] Montanini | Garnet clinopyroxenite layers from the mantle sequences of the Northern Apennine ophiolite (Italy): Evidence for recycling of crustal material[END_REF]. However, residual Grt-pyroxenites are expected to preserve the initial Eu and Sr anomalies that are characteristic of eclogites with a recycled origin [START_REF] Marchesi | Mantle refertilization by melts of crustal-derived garnet pyroxenite: Evidence from the Ronda peridotite massif, southern Spain[END_REF]. In addition, we have identified that the initial cumulative assemblages are, depending on the studied pyroxenites, either Cpx-Opx-Grt-Spl or Cpx-Opx-Spl (±Pl, ±Ol, ±Ap; Table 1), which is not consistent with residual assemblages derived from either gabbroic protoliths [START_REF] Montanini | Garnet clinopyroxenite layers from the mantle sequences of the Northern Apennine ophiolite (Italy): Evidence for recycling of crustal material[END_REF][START_REF] Marchesi | Mantle refertilization by melts of crustal-derived garnet pyroxenite: Evidence from the Ronda peridotite massif, southern Spain[END_REF] or Pl-free pyroxenites or eclogites (Kogiso et al., 2003;[START_REF] Lambart | An experimental study of pyroxenite partial melts at 1 and 1.5 GPa: Implications for the major-element composition of Mid-Ocean Ridge Basalts[END_REF]. Such a model is therefore not valid for the pyroxenites studied here.

TAK-3 and TAK-4 Grt-bearing pyroxenites from Morocco are slightly off the general trends observed for major elements (Fig. 5). These samples are shifted toward Spl and/or Spr compositions in most oxide composition diagrams, suggesting that higher amounts of Spl and/or Spr were present as primary magmatic phases in these samples. The possibility that Spr is a liquidus phase in mafic to intermediate magmas at high pressure conditions (from 1.1 to 3 GPa) has been highlighted by [START_REF] Liu | Liquidus phase relations in the system CaO-MgO-Al2O3-SiO2 at 2.0GPa: applications to basalt fractionation, eclogites, and igneous Sapphirine[END_REF]. However, these authors pointed out that Spr has rarely been described as a magmatic phase in natural rocks as it mostly occurs as a metamorphic mineral. Textural, petrological and geochemical evidence presented here does Garnet Pyroxenites in Old Orogenic Regions not clarify an igneous or metamorphic origin of Spr; this will be further discussed in section

'P-T-t path reconstructions'.

In summary, the studied pyroxenites represent cumulative rocks that initially crystallized Cpx, Opx, and for some samples Grt and Spl (with trace apatite in one sample; Table 1); Pl was part of the initial cumulative assemblage in only one sample (TAK-4). Such cumulative assemblages are not expected in lower crustal (continental & oceanic) settings where Pl is usually the dominant phase. Additionally, Px±Spl±Grt cumulates are expected at shallow mantle depths according to experimental petrology constraints (e.g., [START_REF] Green | The genesis of basaltic magmas[END_REF], and are very commonly described among mantle xenoliths (e.g., [START_REF] Kaeser | Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite[END_REF][START_REF] Perinelli | Thermal evolution of the lithosphere in a rift environment as inferred from the geochemistry of mantle cumulates, Northern Victoria Land, Antarctica[END_REF] or in orogenic ultramafic massifs (e.g., [START_REF] Downes | Origin and significance of spinel and garnet pyroxenites in the shallow lithospheric mantle: Ultramafic massifs in orogenic belts in Western Europe and NW Africa[END_REF]. The likely mantle origin of the studied cumulates can be further tested using isotopic constraints.

Isotopic constraints support a mantle protolith

The oxygen isotopic composition of minerals is useful for constraining mantle versus recycled origins of pyroxenites and eclogites (e.g., [START_REF] Downes | Origin and significance of spinel and garnet pyroxenites in the shallow lithospheric mantle: Ultramafic massifs in orogenic belts in Western Europe and NW Africa[END_REF]Gonzaga et al., 2010a). Cpx, Grt, Opx, and Spl analyzed in this study have oxygen isotopic values typical of mantle minerals (4.8-6.1‰, Fig. 8; e.g., Mattey et al., 1994a;[START_REF] Chazot | Oxygen isotopic composition of hydrous and anhydrous mantle peridotites[END_REF], in contrast to more variable compositions of Cpx and Grt in recycled eclogites (2-10‰; e.g., Mattey et al., 1994b;Gonzaga et al., 2010a) and bulk oceanic crust (3.7-13.6‰; e.g., [START_REF] Gregory | An Oxygen Isotope Profile in a Section of Cretaceous Oceanic Crust, Samail Ophiolite, Oman: Evidence for δ 18 O Buffering of the Oceans by Deep (5 km) Seawater-Hydrothermal Circulation at Mid-Ocean[END_REF].

Deep crustal portions of oceanic crust (primarily Pl-rich cumulates) may display typical mantle values [START_REF] Gao | A complete oxygen isotope profile through the lower oceanic crust, ODP Hole 735[END_REF], but are distinct due to strong Eu anomalies not observed in the pyroxenites studied herein. Major element compositions of the studied pyroxenites do not overlap the composition of neither volcanic, nor plutonic oceanic crust (Fig. 11), also strongly supporting that studied pyroxenites do not derive from recycled oceanic crust. It should be noted here that similar cumulative rocks have been recognized at Moho depth in the Kohistan Garnet Pyroxenites in Old Orogenic Regions overthickened arc crust (35-45 km;[START_REF] Burg | The Asia-Kohistan-India collision: Review and discussion[END_REF]. The studied pyroxenites are therefore most likely mantle cumulates; only TAK-4, which displays mantle like δ 18 O values and magmatic Pl, may represent either a shallow mantle or deep crustal cumulate. Inter-mineral δ 18 O variations are presented in supplementary figure S1; as a whole they are consistent with a mantle origin.

Sr-Nd isotope data obtained on Cpx separates are used to test our previous conclusions. [START_REF] Garrido | Incompatible trace element partitioning and residence in anhydrous spinel peridotites and websterites from the Ronda orogenic peridotite[END_REF] showed that ~65% of the Sr concentration of an ultramafic rock, and ~15% of the Nd, is hosted in solid, melt, and fluid inclusions, as well as grain boundaries; Sr-Nd isotopic data obtained on Cpx separates (the main REE bearing mineral) should thus be preferred to whole rock measurements. As a whole, the studied pyroxenites have Sr and Nd isotopic ratios that are slightly above and below, respectively, the average DMM composition (Fig. 7), in contrast to recycled eclogites that display more heterogeneous values than the host mantle (Gonzaga et al., 2010a). Only two samples, TAK-3 and JO-7b (from Morocco and Jordan, respectively), have higher Nd isotope ratios compared to DMM. The Nd isotopic signature of JO-7b closely matches that of another garnet pyroxenite from Israel (BS-701 in [START_REF] Stein | Chronothermometry of peridotitic and pyroxenitic xenoliths: Implications for the thermal evolution of the Arabian lithosphere[END_REF] and peridotite samples from Saudi Arabia [START_REF] Henjes-Kunst | Evolution and composition of the lithospheric mantle underneath the western Arabian peninsula: constraints from Sr-Nd isotope systematics of mantle xenoliths[END_REF][START_REF] Blusztajn | Trace-element and isotopic characteristics of spinel peridotite xenoliths from Saudi Arabia[END_REF], and is probably a time integrated effect of a high Sm/Nd ratio (Sm/Nd = 0.566; e.g., [START_REF] Borghini | Meter-scale Nd isotopic heterogeneity in pyroxenite-bearing Ligurian peridotites encompasses global-scale upper mantle variability[END_REF], which is the highest among all the samples. TAK-3 from Morocco does not have a high Sm/Nd ratio, but its isotopic composition is very close to that of lherzolite and websterite samples analyzed in the same area [START_REF] Raffone | Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe-and Mg-rich Wehrlites[END_REF].

Excluding TAK-3 and JO-7b, the Sr-Nd isotopic compositions of the studied pyroxenites, although heterogeneous, overlap those obtained on mantle rocks from the various areas considered (Fig. 7), as is expected for pyroxenites with origins as segregations from mantle melts (e.g., [START_REF] Downes | Origin and significance of spinel and garnet pyroxenites in the shallow lithospheric mantle: Ultramafic massifs in orogenic belts in Western Europe and NW Africa[END_REF]Gonzaga et al., 2010a).

Garnet Pyroxenites in Old Orogenic Regions

Our findings are in agreement with numerous previous studies identifying mantle pyroxenites as mantle cumulates rather than the products of deep crustal recycling [START_REF] O'hara | Formation and fractionation of basic magmas at high pressure[END_REF][START_REF] Frey | The origin of pyroxenites and garnet pyroxenites from Salt Lake Crater, Oahu, Hawaii: trace element evidence[END_REF][START_REF] Downes | Origin and significance of spinel and garnet pyroxenites in the shallow lithospheric mantle: Ultramafic massifs in orogenic belts in Western Europe and NW Africa[END_REF][START_REF] Griffin | Cratonic lithospheric mantle : Is anything subducted?[END_REF][START_REF] Perinelli | Thermal evolution of the lithosphere in a rift environment as inferred from the geochemistry of mantle cumulates, Northern Victoria Land, Antarctica[END_REF]. The opposing view that mantle heterogeneities originate mainly from recycling associated with subduction zones [START_REF] Allègre | Implications of a two-component marble-cake mantle[END_REF] is not applicable to most of the studied samples.

Evidence for subsequent metasomatic interactions

Most of the studied pyroxenites show evidence of late melt percolation and cryptic and/or modal metasomatism. Two samples from Cameroon (YK-13 and YK-16) are LREE enriched and sample YK-05, although LREE depleted, shows a slight enrichment in La compared to Ce. These LREE enriched samples also have high concentrations in Ba, Sr, U and Th and low concentrations in Zr and Hf. This metasomatic signature has already been observed in spinel lherzolites from the Nyos volcano along the CVL [START_REF] Temdjim | L'hétérogénéité du manteau supérieur à l'aplomb du volcan de Nyos (Cameroun) révélée par les enclaves ultrabasiques[END_REF], and is therefore a regional overprint. The Morocco pyroxenites are also enriched in LREE, Ba, U, Th and Sr, although more markedly in TAK-4 than in TAK-3. [START_REF] Raffone | Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe-and Mg-rich Wehrlites[END_REF] documented similar enrichments in peridotite xenoliths from the same volcanic province and showed that they are related to alkaline melt percolation, probably associated with late Cretaceous or Eocene volcanism. A metasomatic overprint is also present in three of the four studied Jordan samples. Spidergrams highlight the LREE enrichment relative to MREE, and positive Ba, U, and Th anomalies that are similar to metasomatic enrichments previously described in Jordan lithospheric mantle, and possibly related to Pan-African subduction [START_REF] Shaw | The geochemistry of the Arabian lithospheric mantle-a source for intraplate volcanism[END_REF].

Metasomatism is also evident in the pyroxenites from the FMC. All the whole-rocks, except the southernmost sample (Le Pouget), have spoon-shaped REE patterns with decreasing REE content from Lu to Nd, and are enriched in LREE (La, Ce and Pr), clearly pointing to LREE Garnet Pyroxenites in Old Orogenic Regions depleted protoliths, further enriched by LREE-rich percolating melts. These samples are also highly enriched in U and Th, and sometimes depleted in Nb, Zr and Hf.

LN-78 is a composite sample with an Am-bearing and an Am-free part. In the Am-bearing part, Cpx is more LREE-enriched, and is in chemical equilibrium with coexisting Am as attested by the 1 /  Am Cpx REE D [START_REF] Chazot | Determination of partition coefficients between apatite, clinopyroxene, amphibole and melt in natural spinel lherzolites from Yemen: Implications for wet melting of the lithospheric mantle[END_REF]. In the Am-free part, Cpx has complex REE patterns with HREE decreasing from Eu to Lu due to preferential incorporation of these elements in coexisting Grt. Rare earths were initially decreasing from Eu to La (similar to Le Pouget sample), but La and Ce have been selectively enriched during melt percolation and crystallization of Am and Cpx in the Am-bearing part of the sample; similar conclusions have been proposed by [START_REF] Downes | Mantle domains in the lithosphere beneath the French Massif Central: trace element and isotopic evidence from mantle clinopyroxenes[END_REF]. Similar metasomatic overprints with LREE, U, and Th enrichments, and Zr-Hf and Nb-Ta depletions have been observed in peridotite xenoliths from different localities in the FMC [START_REF] Lenoir | Contrasting domains beneath the Massif Central (France) revealed by geochemistry of peridotites xenoliths[END_REF][START_REF] Féménias | A Permian underplating event in the late-to post-orogenic tectonic setting. Evidence from the mafic-ultramafic layered xenoliths from Beaunit (French Massif Central)[END_REF][START_REF] Dautria | 160 Ma of sporadic basaltic activity on the Languedoc volcanic line (Southen France): A peculiar case of lithosphere-asthenosphere interplay[END_REF]; those overprints are ascribed for most of the elements to Variscan (or late Variscan) -possibly subduction-related --metasomatism [START_REF] Lenoir | Contrasting domains beneath the Massif Central (France) revealed by geochemistry of peridotites xenoliths[END_REF][START_REF] Féménias | A Permian underplating event in the late-to post-orogenic tectonic setting. Evidence from the mafic-ultramafic layered xenoliths from Beaunit (French Massif Central)[END_REF].

Other authors link this metasomatic event to the arrival of a mantle plume head in the early Cenozoic [START_REF] Dautria | 160 Ma of sporadic basaltic activity on the Languedoc volcanic line (Southen France): A peculiar case of lithosphere-asthenosphere interplay[END_REF]. Some xenoliths originated in the southern part of the FMC do not show any metasomatic overprint [START_REF] Dautria | 160 Ma of sporadic basaltic activity on the Languedoc volcanic line (Southen France): A peculiar case of lithosphere-asthenosphere interplay[END_REF], in agreement with the lack of enrichment in the Le Pouget sample.

A metasomatic overprint may be hard to distinguish from a trapped melt component present in the initial cumulative assemblage. Na content may be used as it is not expected to be particularly enriched by metasomatic fluid percolation in comparison to other major elements, however it is useful to track a trapped melt component in cumulates (see section 8.2.1, and Fig. 5). Among the studied samples only LP-27, and YK-13 have been shown to record a trapped melt component; all trace element characteristics discussed above for the other samples are likely related to metasomatic enrichments.

As discussed in [START_REF] Pezzali | Analogues of exhumed pyroxenite layers in the Alboran domain sampled as xenoliths by Middle Atlas Cenozoic volcanism[END_REF], the samples displaying the weakest metasomatic overprint can be considered as geochemical remnants of the pre-metasomatic lithospheric mantle. Those are Le Pouget sample for FMC lithospheric mantle, Jo-7b for Jordan lithospheric mantle, YK-01, and YK-12 for Cameroon lithospheric mantle.

P-T-t path reconstructions and pyroxenite evolution within mantle domains

Various geochemical data presented here have highlighted an origin as mantle fractionated melts for the studied samples. Precise petrological observations and whole rock trace element contents are here used to constrain the P evolution of these cumulates and to reconstruct the corresponding P-T-t paths. To proceed, the P-T stability fields, the associated facies and subfacies, and the corresponding subsolidus reactions separating lithospheric mantle domains, documented in Fig. 12a, will be considered. Initial cumulative assemblages, and the sequence of subfacies crossed during the P-T-t evolution are recalled in Table 1.

FMC pyroxenites display recrystallized textures resulting from various sub-solidus mineral reactions. Grt entered the mineral assemblage as a liquidus phase (section 8.2), consistent with a first crystallization of the FMC pyroxenites in the Ariegite subfacies (Fig. 12b). However the numerous inclusions (green Spl, Cpx, Opx and Pl; Fig. 2a-b) observed in Grt show that the present-day Ariegite-subfacies mineral assemblage (Cpx+Grt+Opx+Spl±Am) does not represent that of the initial cumulate, but rather derivates from metamorphic reactions. This mineral assemblage preserved as inclusions in Grt thus testifies for an early Seiland pyroxenite facies assemblage. Some large Cpx grains (up to 2 mm) containing Opx exsolutions (Fig. 2c) have escaped the general recrystallization process and are still reminiscent of an early cooling. A demixing T of ~1275°C is estimated for sample LN-78 using image processing, mineral compositions, and [START_REF] Carlson | Thermochemistry of pyroxenes on the join Mg2Si2O6-CaMgSi2O6[END_REF] relations. In all the FMC samples but Le Pouget pyroxenite, Grt grains in contact with Cpx grains undergo Garnet Pyroxenites in Old Orogenic Regions a later reaction leading to the local development of Pl, Opx and brown Spl (Fig. 12b), marking the return of the samples into the Seiland P-T domain. P-T-t paths for FMC samples are therefore summarized as follows (Fig. 12b): samples crystallized in Ariegite subfacies conditions (magmatic Grt), suffered an early T decrease (large Cpx grains with Opx exsolutions), and then underwent a concomitant P and T decrease that allowed a transition towards the Seiland subfacies (testified by Opx-Spl-Pl inclusions in present-day Grt); a further decrease in T brought the samples back into the Ariegite domain crystallizing the present-day

Grt that contains relics of the former Seiland stage (Opx-Spl-Pl in Grt). A final decompression (or reheating) event that once again shifted some samples into the Seiland stability field.

A similar approach is followed to reconstruct the P-T-t evolution of the Morocco samples (Fig. 12c). Grt was a liquidus phase in TAK-3 (Ariegite facies conditions; section 8.2) but was absent when TAK-4 crystallized at a shallower depth. TAK-3 also contains some large Cpx grains with Opx exsolutions, indicating a T decrease after crystallization. Grt currently present in TAK-3 are mainly located around Spl (Fig. 2e-f) and formed by the reaction Opx+Spl+Pl->Grt+Cpx that documents the transition from the Seiland to the Ariegite subfacies (a previous transition from the Ariegite facies crystallization conditions to the Seiland subfacies is not documented by the mineralogy). Although TAK-4 did not crystallize in Ariegite facies conditions (no liquidus Grt, but magmatic Pl), abundant and large Grt and Cpx grains associated with the absence of Ol provide evidence of subsolidus equilibration under those conditions. The presence of a small Spr rim between Spl and Grt (Fig. 2e-f) suggests that the transition from Seiland to Ariegite subfacies conditions was mainly governed by a decrease in T inducing the reaction Opx+Spl+Pl->Grt+Spr; this is consistent with the Al-rich composition of TAK-4 Opx that is required for such a reaction [START_REF] France | CMAS 3D a new program to rapidly visualise and project major elements compositions in the CMAS system[END_REF]. Alternatively, if TAK-4 was crystallized at deep crustal levels (see section 8.2.2), the cooling stage associated with this reaction may have been associated with a pressure increase. We will hereafter consider

Garnet Pyroxenites in Old Orogenic Regions

only the less complex model that necessitates only a cooling stage. The presence of numerous Spr inclusions in Spl (Fig. 2e-f) and of one Spr relic surrounded by small crystals of Opx, Spl and Pl within a Cpx grain (Fig. 2a) document a further reaction, namely Grt+Spr->Opx+Spl+Pl, before the sample equilibrated in the Ariegite subfacies. This reaction marks the transition from the Spr-bearing Ariegite subfacies to the Spr-absent Ariegite subfacies, probably in response to a decrease in P. Despite those P-T-t estimates, Spr-bearing TAK-4 appears to have a rather complex paragenesis evolution. Further constraints from thermodynamic models will be needed to decipher a more precise evolution, however such work is beyond the scope of the present study. P-T-t paths for Morocco pyroxenites are therefore mostly characterized by a cooling event subsequent to crystallization that it is possibly followed by a concomitant P and T decrease before re-equilibration at lower T.

Pyroxenites from Cameroon contain large amounts of Cpx that exsolves Grt and sometimes Opx. Grt was not a liquidus phase when these cumulates crystallized, as shown by their relatively flat whole rock REE patterns (Fig. 6), constraining their formation in the Seiland subfacies (Fig. 12b). As previously discussed for the FMC and Morocco samples, exsolution of Opx is related to a decrease in T after crystallization. The occurrence of Grt is also related to a strong cooling event when it exsolved from Cpx or crystallized around Spl while the samples were moved to the Ariegite facies. This evolution can be accounted for by an isobaric T decrease or a concomitant T and P decrease. P-T-t paths for Cameroon pyroxenites therefore record a rather simple P-T-t trajectory marked mainly by a decrease in T (Fig. 12b).

Evolution in pressure is poorly constrained, and a slight decompression may have occurred.

Pyroxenites from Jordan show only limited mineralogical reactions that can be used to decipher their P-T-t evolution (Fig. 12c). Pyroxenes from JO-12h are the most magnesian among the studied samples, Spl contains the highest amount of Cr 2 O 3 , and ~10% Ol is present; altogether those observations point to a parental melt that was slightly more primitive Garnet Pyroxenites in Old Orogenic Regions than for other samples. In this pyroxenite, the absence of Pl and the presence of Ol+Cpx+Opx+Spl indicates that the reaction separating the Seiland subfacies and the Pllherzolite facies (Cpx+Opx+Spl->Ol+Pl) has not occurred. JO-12h therefore equilibrated in the Seiland subfacies. Grt was not a liquidus phase in any of the Jordan samples (Fig. 6; section 8.2), also implying crystallization in the Seiland subfacies. When present, Grt appears as exsolutions in pyroxene or around Spl (JO-7b and JO-7h), and so is clearly a subsolidus mineral. Grt exsolutions in pyroxenes are also indicative of a marked cooling event from the Seiland to the Ariegite field. Also consistent with an important cooling event are the numerous rutile exsolution lamellae in Opx of JO-10e (Fig. 2l). Indeed during crystallization at high pressure, in the absence of Ol and Spl, Ti is accommodated by Opx, and can be exsolved to form rutile exsolution needles during cooling [START_REF] Verhoogen | Distribution of titanium between silicates and oxides in igneous rocks[END_REF][START_REF] Moore | Rutile exsolution in Orthopyroxene[END_REF].

P-T-t paths of Jordan samples are therefore mainly governed by a strong temperature decrease but are not well constrained in pressure (Fig. 12c). As is the case for Cameroon samples, a slight decrease in pressure may have occurred during thermal equilibration toward cooler conditions (Fig. 12c).

Inter-and intra-sites variability

Invoking a common cumulative process for the formation of the studied pyroxenites may sound odd given the inter-and intra-region petrographical and geochemical variability of the samples. Nevertheless, partial crystallization of mantle derived melts during interactions with peridotites at various depths has the potential to crystallize such apparently heterogeneous cumulates [START_REF] Downes | Origin and significance of spinel and garnet pyroxenites in the shallow lithospheric mantle: Ultramafic massifs in orogenic belts in Western Europe and NW Africa[END_REF]. In particular, whole rock compositions (major and trace elements) are only representative of the initial cumulative assemblage (± metasomatism) that has been sampled by a given xenolith (Fig. 13). An extreme case would be that a small size xenolith might sample only one mineral of this initial cumulative assemblage (e.g., Cpx, Opx, Grt, Spl; cases 1, 2, 3 in Fig. 13). A more likely case would be that a xenolith samples a poly-mineral piece of the initial cumulative assemblage (cases 4, 5 in Fig. 13). In that case, the whole rock composition represents a mixing of the mineral compositions that relies on the modal proportion within the initial cumulative assemblage (Fig. 13b-c). One striking feature is that the modal composition of a given xenolith does not represent the modal proportion of the initial cumulative assemblage as cumulates have suffered several metamorphic reactions during their subsolidus evolution (Fig. 12, 13). The present day modal composition of a given sample is therefore not directly representative of the whole rock composition (e.g., TAK-4 contains 56 % Grt when the trace element content shows that Grt was not part of the initial cumulative assemblage). The widespread metasomatic events that have affected most of the samples are expected to modify mainly the trace element budgets (e.g., LREE enrichments; samples 1, 2, 4, 5 in Fig. 13c).

Given the various crystallization pressures (Seiland versus Ariegites subfacies; Table 1), the numerous initial modal proportions that a given xenolith may sample (Fig. 13), and the range of metasomatic enrichments that can affect the samples (Fig. 13c, and section 8.3), it is likely that the samples display a strong inter-and intra-region variability, though they share a common genesis.

Geodynamic implications

Late-orogenic genesis of pyroxenites

Petrological and geochemical evidences reported above, highlight that all the studied pyroxenite xenoliths are products of melt crystallization at mantle conditions (1)[START_REF] Ballentine | Hafnium isotopic studies of the Cameroon line and new HIMU paradoxes[END_REF].

Similar cumulative rocks to those studied here have been recognized at Moho depth in overthickened arc crust [START_REF] Burg | The Asia-Kohistan-India collision: Review and discussion[END_REF] where they crystallized prior to the thinning and exhumation of the thickened crust. Cumulates have later undergone subsolidus evolution Garnet Pyroxenites in Old Orogenic Regions under progressively changing P and T conditions; reconstructed P-T-t paths therefore also highlight the P-T-t evolution of the regional host mantle, and can be used to discuss the geodynamic settings that resulted in pyroxenite crystallization. Two P-T-t path types are observed among the samples: the first is characterized by a strong cooling event that may have been accompanied by a pressure decrease (Cameroon and Jordan samples; Fig. 12), and the second is characterized by two important cooling stages separated by a period during which P and T decrease jointly (FMC and Morocco samples; Fig. 12). The four studied areas have been implicated in orogenic episodes in the last 800 Ma (either Panafrican or Hercynian). In this perspective, the crystallization of mantle melts at depth, followed by a strong decrease in T, and then by a decompression stage, can only occur during the exhumation of an orogenic domain, and the associated thermal re-equilibration. Similar P-T paths for mantle rocks have been described in different areas [START_REF] Müntener | The Malenco peridotites (Alps). Petrology and geochemistry of subcontinental mantle and Jurassic exhumation during rifting[END_REF][START_REF] Fabriès | Petrogenetic evolution of orogenic lherzolite massifs in the central and western Pyrenees[END_REF][START_REF] Kaeser | Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite[END_REF], and major magmatic episodes (e.g., magmatic underplating) are well known to occur in the late evolution of orogenic domains (e.g., [START_REF] Henk | Magmatic underplating, extension, and crustal reequilibration: Insights from a cross-section through the Ivrea zone and Strona-Ceneri Zone, Northern Italy[END_REF][START_REF] Fabriès | Petrogenetic evolution of orogenic lherzolite massifs in the central and western Pyrenees[END_REF][START_REF] Cottin | Isotopic (O, Sr, Nd) and trace element geochemistry of the Laouni layered intrusions (Pan-African belt, Hoggar, Algeria): evidence for postcollisional continental tholeiitic magmas variably contaminated by continental crust[END_REF][START_REF] Féménias | A Permian underplating event in the late-to post-orogenic tectonic setting. Evidence from the mafic-ultramafic layered xenoliths from Beaunit (French Massif Central)[END_REF][START_REF] Kaeser | Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite[END_REF][START_REF] Mccarthy | Ancient depletion and mantle heterogeneity: Revisiting the Permian-Jurassic paradox of Alpine peridotites[END_REF]. Along with underplating occurring at Moho depth, large circulations of melts in deeper mantle domains are expected and associated with refertilization reactions (e.g., [START_REF] Mccarthy | Ancient depletion and mantle heterogeneity: Revisiting the Permian-Jurassic paradox of Alpine peridotites[END_REF]. The melting event may start during the first stage of exhumation when mantle is upwelling roughly adiabatically (isostatic re-equilibration). Post-crystallization equilibration to the local geothermal T is recorded by the first part of the cooling stage. Following crystallization and cooling, Morocco and FMC (and possibly Cameroon and Jordan) samples underwent decompression tentatively related to the continuation of erosion and tectonic collapse of the orogenic edifices. All the studied cumulates record the late orogenic stage corresponding to the thermal re-equilibration along the continental geotherm (last cooling stage). FMC samples from the Devès volcanic field have recorded a late P decrease; this event Garnet Pyroxenites in Old Orogenic Regions could be linked to the Cenozoic bulging affecting the FMC (e.g., [START_REF] Sobolev | Upper mantle temperatures from teleseismic tomography of French Massif Central including effects of composition, mineral reactions, anharmonicity, anelasticity and partial melt[END_REF][START_REF] Seranne | The Gulf of Lion continental margin (NW Mediterranean) revisited by IBS: an overview[END_REF]. This is consistent with the absence of this last P drop in the southernmost sample (Le Pouget), as no bulging has been described in the southern part of the FMC (e.g., [START_REF] Sobolev | Upper mantle temperatures from teleseismic tomography of French Massif Central including effects of composition, mineral reactions, anharmonicity, anelasticity and partial melt[END_REF][START_REF] Seranne | The Gulf of Lion continental margin (NW Mediterranean) revisited by IBS: an overview[END_REF].

The late-orogenic origin of the studied cumulates can be challenged by chronological constraints; indeed Nd isotopic compositions can be used to put some constraints on the timing of these events (e.g., [START_REF] Bizimis | Hf-Nd-Sr isotope systematics of garnet pyroxenites from salt lake crater, Oahu, Hawaii: Evidence for a depleted component in Hawaiian volcanism[END_REF]. Although these estimates should be considered with serious caution (e.g., [START_REF] Wittig | Dating the mantle roots of young continental crust[END_REF][START_REF] Downes | Origin and significance of spinel and garnet pyroxenites in the shallow lithospheric mantle: Ultramafic massifs in orogenic belts in Western Europe and NW Africa[END_REF], building time estimates using Nd in Cpx seems appropriate as those minerals host ~80% of the whole rock Nd budget [START_REF] Garrido | Incompatible trace element partitioning and residence in anhydrous spinel peridotites and websterites from the Ronda orogenic peridotite[END_REF]. Assuming that in each region the pyroxenites formed from a similar melt with homogeneous isotopic composition, samples from Cameroon have crystallized between 700 and 1000 Ma ago. Such an estimation is valid for Jordan pyroxenites, for which the origin can be estimated between 550 and 650 Ma. Morocco samples are strongly overprinted by metasomatic circulations, and although time estimates are consistent with late Panafrican orogeny (~520 Ma), those samples will not be considered here.

For Cameroon and Jordan, these rough time estimates correspond, with large uncertainties, to the main Panafrican orogenic events affecting the crust and the upper mantle in these areas.

Again, these time constraints should be considered with serious caution as most of the samples have been affected by post-crystallization metasomatism, which may have modified Sm/Nd ratios and Nd isotopic compositions.

As a whole, the pyroxenites were formed in mantle conditions during late-orogenic magmatism associated with orogenic exhumation (Fig. 14a-c). The recorded orogenic cycle is probably the last main one in each region, and may be Panafrican for Jordan, Morocco and Cameroon, and Hercynian for FMC. During their subsequent evolution, cumulates have suffered several interactions with percolating fluids and melts.

Garnet Pyroxenites in Old Orogenic Regions

Mantle refertilization and forthcoming magma genesis

We have shown that the studied Grt pyroxenites are mantle cumulates that crystallized during the relaxation following orogenic events, and subsequently underwent modal and cryptic metasomatism. Pyroxenites are fertile lithologies as their solidus is crossed at lower T than the lherzolite solidus; up to 15% pyroxenite partial melting can be reached before the onset of lherzolite melting [START_REF] Hirschmann | A possible role for garnet pyroxenites in the origin of the 'garnet signature' in MORB[END_REF]. The addition of a pyroxenite component in a given mantle domain consequently corresponds to a refertilization stage (e.g., [START_REF] Bodinier | Origin of Pyroxenite-Peridotite Veined Mantle by Refertilization Reactions: Evidence from the Ronda Peridotite (Southern Spain)[END_REF], and the presence of pyroxenitic and metasomatic lithologies in the mantle has strong implications on basalt genesis (either MORB or OIB; [START_REF] Allègre | Implications of a two-component marble-cake mantle[END_REF][START_REF] Hirschmann | A possible role for garnet pyroxenites in the origin of the 'garnet signature' in MORB[END_REF][START_REF] Hirschmann | Alkalic magmas generated by partial melting of garnet pyroxenite[END_REF][START_REF] Kogiso | High-pressure partial melting of garnet pyroxenite: possible mafic lithologies in the source of ocean island basalts[END_REF][START_REF] Kogiso | High-pressure Partial Melting of Mafic Lithologies in the Mantle[END_REF][START_REF] Pilet | Metasomatized Lithosphere and the Origin of Alkaline Lavas[END_REF]. The present study thus highlights that a refertilization stage of lithospheric mantle can occur during the late orogenic re-equilibration period. It follows that subsequent magmatic activity can be enhanced in old orogenic regions (such as FMC, Morocco, Cameroon, Jordan), as it can be initiated earlier, and may be characterized by higher magma volumes than in a non-affected region (Fig. 14). Nevertheless, tracking the implication of such fertile lithologies in recent volcanism remains elusive as the melt-peridotite reactions that occurred during melt ascent prevent the geochemical tracking of this influence (e.g., Le [START_REF] Le Roux | Isotopic decoupling during porous melt flow: A case-study in the Lherz peridotite[END_REF][START_REF] Lambart | An experimental study of pyroxenite partial melts at 1 and 1.5 GPa: Implications for the major-element composition of Mid-Ocean Ridge Basalts[END_REF].

Conclusions

The petrographical, geochemical, and isotopic study of garnet bearing pyroxenite xenoliths from four localities (FMC, Morocco, Jordan and Cameroon) allows characterization of their genesis and subsequent evolution. The whole-rock major element compositions and compatible element abundances, the absence of Pl in the initial cumulative assemblage for all the samples (but one sample from Morocco), and mineral oxygen isotopic compositions highlight a cumulative mantle origin. Metamorphic reactions, exsolutions and trace element whole-rock concentrations demonstrate that crystallization pressures ranged between 1 and 2 GPa (30-60 km depth) depending on the samples. P-T-t paths based on well characterized petrographical relations and calculated equilibrium temperatures attest to important movements in the respective lithospheres, whereas the presence of some hydrous minerals such as amphiboles, and incompatible element concentrations attest to a metasomatic overprint in most of the samples; this metasomatic enrichment also affects the host mantle. In their geodynamical context, the samples are interpreted as representing the crystallization of percolating melts formed at mantle conditions during exhumation of orogenic domains.

Although variable due to the long-term integration of various father/daughter ratios, the Sr and Nd isotope signatures are consistent with crystallization during Panafrican times for Cameroon, Morocco and Jordan samples.

The results presented here highlight that exhumation of orogenic domains and the associated sub-adiabatic decompression trigger mantle partial melting; the melt percolating the mantle crystallizes, at least partially, to form the studied cumulative pyroxenites. At mantle conditions, pyroxenites are low melting point lithologies; their crystallization in mantle domains therefore implies its refertilization. As a consequence, the magmatism in old orogenic regions such as FMC, Morocco, Cameroon and Jordan, will be enhanced, and old orogenic domains would be precursor zones for magmatism that would be initiated earlier and would be volumetrically larger than in non-affected areas. Trapped melt seems to influence the Na 2 O content for some samples. [START_REF] Hart | Mantle plumes and entrainment: isotopic evidence[END_REF]. Data are compared to regional mantle compositions (i.e., mantle xenoliths) in a), and to regional lava compositions in b). Literature data: Mantle rocks (a) from Jordan [START_REF] Henjes-Kunst | Evolution and composition of the lithospheric mantle underneath the western Arabian peninsula: constraints from Sr-Nd isotope systematics of mantle xenoliths[END_REF][START_REF] Stein | Chronothermometry of peridotitic and pyroxenitic xenoliths: Implications for the thermal evolution of the Arabian lithosphere[END_REF][START_REF] Blusztajn | Trace-element and isotopic characteristics of spinel peridotite xenoliths from Saudi Arabia[END_REF][START_REF] Baker | Metasomatism of the shallow mantle beneath Yemen by the Afar Plume-Implications for mantle plumes, flood volcanism, and intraplate volcanism[END_REF], Morocco [START_REF] Raffone | Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe-and Mg-rich Wehrlites[END_REF], and

Captions:

Cameroon [START_REF] Lee | Melt enrichment of shallow depleted mantle: A detailed petrological, trace element and isotopic study of mantle derived xenoliths and megacrysts from the Cameroon Line[END_REF]; and lava compositions (b) from Morocco [START_REF] El Azzouzi | Evolution des sources du volcanisme marocain au cours du Néogène[END_REF], Cameroon [START_REF] Halliday | Mantle dynamics: a Nd, Sr, Pb and O isotopic study of the Cameroon line volcanic chain[END_REF][START_REF] Lee | Isotopic variations with distance and time in the volcanic islands of the Cameroon line: Evidence for a mantle plume origin[END_REF][START_REF] Ballentine | Hafnium isotopic studies of the Cameroon line and new HIMU paradoxes[END_REF][START_REF] Marzoli | The Cameroon Volcanic Line Revisited: Petrogenesis of Continental Basaltic Magmas from Lithospheric and Asthenospheric Mantle Sources[END_REF][START_REF] Rankenburg | The role of continental crust and lithospheric mantle in the genesis of Cameroon Volcanic Line lavas: constraints from isotopic variations in lavas and megacrysts from the Biu and Jos plateaux[END_REF][START_REF] Kamgang | Geochemistry and geochronology of mafic rocks from Bamenda Mountains (Cameroon): Source composition and crustal contamination along the Cameroon Volcanic Line[END_REF], Jordan [START_REF] Shaw | Petrogenesis of the largest intraplate volcanic field on the Arabian Plate (Jordan): A mixed lithosphere-asthenosphere source activated by lithospheric extension[END_REF][START_REF] Krienitz | Tectonic events, continental intraplate volcanism, and mantle plume activity in northern Arabia: Constraints from geochemistry and Ar-Ar dating of Syrian lavas[END_REF]. [START_REF] Ionov | Oxygen isotope composition of garnet and spinel peridotites in the continental mantle: Evidence from the Vitim xenolith suite, southern Siberia[END_REF]Mattey et al., 1994a;[START_REF] Chazot | Oxygen isotopic composition of hydrous and anhydrous mantle peridotites[END_REF][START_REF] Zhang | Recent fluid processes in the Kaapvaal Craton, South Africa: coupled oxygen isotope and trace element disequilibrium in polymict peridotites[END_REF]. S1. [START_REF] Godard | Geochemistry of a long in-situ section of intrusive slowspread oceanic lithosphere: Results from IODP Site U1309 (Atlantis Massif, 30°N Mid-Atlantic-Ridge)[END_REF]n=173). (1): Pl+OlCpx+Opx+Spl between A and B (e.g., [START_REF] Takazawa | Evolution of the Horoman peridotite (Hokkaido, Japan); implications from pyroxene compositions[END_REF]; [START_REF] Ballentine | Hafnium isotopic studies of the Cameroon line and new HIMU paradoxes[END_REF]:

Garnet Pyroxenites in Old Orogenic Regions

Opx+Spl+PlCpx+Grt between B and C (e.g., [START_REF] O'hara | Mineral facies in ultrabasic rocks[END_REF]; and (3):

Garnet Pyroxenites in Old Orogenic Regions Cpx+Opx+SplOl+Grt between C and D (e.g., Johnson et al., 1990). The black line (4) is the "sapphirine reaction", namely Opx+Pl+SplSpr+Grt; it occurs only at high temperature and at slightly higher pressure than reaction [START_REF] Ballentine | Hafnium isotopic studies of the Cameroon line and new HIMU paradoxes[END_REF]. S is solidus. The TAK-4 path needs further constraint, the early P drop is poorly documented and a pure cooling stage is possible for this sample (dotted line). 1). In our theoretical evolution all the samples, but xenolith 3, have suffered metasomatic interactions. REE elements evolution is only qualitative, and based on minerals' Kds, and on the consideration that metasomatism is associated to LREE enrichment. orogen is formed. At stage 2, the exhumation triggers a sub-isotherm decompression in the mantle, resulting in partial melting; the formed melt percolates the mantle section, and crystallizes the studied pyroxenites. After stage 2, studied pyroxenites are crystallized and their subsequent P-T-t evolution can be followed on Figure 12; their petrographical and geochemical evolution can be followed on Figure 13. Between stage 2 and 3, the exhumation is continuous until a thermal re-equilibration. After stage 3 the lithosphere is in a thermal classical regime, and contains heterogeneities (i.e., the studied pyroxenites), at that stage mantle domains can suffer metasomatism reactions (=stage 3'). Stage 4: the subsequent lithospheric evolution (thermal anomaly or rifting initiation), and with modified physical properties. In particular, the presence of pyroxenite cumulates lowers the global solidus.

Compared to lherzolitic mantle regions ('un-refertilized lherzolite mantle'), partial melts will therefore occur earlier (at lower temperature), and melt production will be higher for a given temperature in such refertilized areas ('refertilized mantle'). 1.

n is the number of analyses that is averaged. In the comment column, Opx 1 and Pl 1 indicate minerals observed as inclusions in Grt; reactional indicates minerals observed in the finegrained Opx-Pl-Spl assemblages in FMC samples (Figure 2d). Data for Le Pouget sample are Garnet Pyroxenites in Old Orogenic Regions from [START_REF] Fabriès | Petrology and thermal history of highly deformed mantle xenoliths from the Montferrier basanites, Languedoc, southern France: A comparison with Ultramafic Complexes from the north Pyrenean Zone[END_REF]. %Ph is the An content for Pl, the #Cr for Spl, and the #Mg for other phases (molar basis); %Ph2 is the jadeite content for Px, the pyrope content for Grt, and the K-feldspar content for Pl. ). The average reproducibility of oxygen isotope analyses of silicate minerals is 0.16‰. Standards were analyzed at the beginning and end of each analytical series; these were the in-house laboratory standard QMS quartz (theoretical δ 18 O value =14.05 ‰), and UWG-2 garnet (theoretical δ 18 O value=5.8 ‰).

The Sr-Nd radiogenic isotopic analyses have been achieved at LMV using a thermo ionization mass spectrometer (TIMS) Triton from Thermo-Finnigan. Each analysis has been accomplished on 100 mg of separate Cpx. Sr and Nd were extracted following a chromatographic extraction method after having effectuated a leaching: 30min in HCl 2.5N, 15min in HF 5%, 30min in HCl 2.5N and 30min in distilled water. Samples were then evaporated on tungsten filaments and analyzed using the double filament method with the TIMS Finnigan Triton. Standards used for this study are BIR-1 0.703136±4 and NBS987 0.710279±4 for Sr and BIR-1 0.513111±4 and AMES 0.511960±3 for Nd. This study [START_REF] Harte | Partitioning of trace elements between clinopyroxene and garnet: data from mantle eclogites[END_REF][START_REF] Huang | Exsolution lamellae in a clinopyroxene megacryst aggregate from Cenozoic basalt, Leizhou Peninsula, South China: petrography and chemical evolution[END_REF][START_REF] Viljoen | Contrasting Group I and Group II eclogite xenoliths petrogenesis: Petrological, trace element and isotopic evidence from eclogite, garnet-websterite and alkremite xenoliths in the Kaalvallei kimberlite, South Africa[END_REF][START_REF] Johnson | Experimental cpx/and garnet/melt partitioning of REE and other trace elements at high pressures: petrogenetic implications[END_REF] KD Cpx/Gt O Orthopyroxene Yemen lherzolites (Chazot et al.,97)

Figure 1 :

 1 Figure 1: Simplified maps and sampling localities (red stars) for FMC samples (a, modified

Figure 2 :

 2 Figure 2: Photomicrographs of the studied samples. a) Pl inclusion with radial fractures in the

Figure 3 :

 3 Figure 3: Mineral chemistry. a) Cpx and Opx compositions in molar proportions (Wo:

Figure 4 :

 4 Figure 4: Chondrite-normalized (Anders and Grevesse, 1989) REE (a, c, e), and trace

Figure 5 :

 5 Figure 5: Whole rock major element and Ni composition diagrams (Table4). In all diagrams,

Figure 6 :

 6 Figure 6: Chondrite-normalized (Anders and Grevesse, 1989) REE (a, c, e) and trace element

Figure

  Figure 7: 143 Nd/ 144 Nd versus 87 Sr/ 86 Sr for clinopyroxene separates from Morocco, Jordan, and

Figure 8 :

 8 Figure 8: Oxygen isotopic composition of the constituent minerals in the studied pyroxenites, δ 18 O is expressed in ‰. Oxygen isotopic composition of corresponding minerals in peridotites

Figure 9 :

 9 Figure 9: Redox conditions. Details about calculations are given in text, and values are

Figure 10 :

 10 Figure 10: Partitioning (K D ) of trace elements between Cpx and Grt, and between Cpx and

Figure 11 :

 11 Figure 11: Whole rock and Ni composition diagrams for studied pyroxenites, and various

Figure 12 :

 12 Figure 12: P-T-t paths for the studied pyroxenites. Phase diagram for the ultramafic system is

Figure 13 :

 13 Figure 13: Schematic evolution of the petrographic assemblage (a), and qualitative evolution

Figure 14 :

 14 Figure 14: General schematic evolutionary model for the studied pyroxenites. At stage 1, an

  al., Fig. 4

  Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

  7

(

  Rb Sr Y Zr Nb Ba La Ce Pr NdSmEu Gd Tb Dy Ho Er TmYb Lu Hf Ta Pb Th U

France

  Ta La Ce Sr Nd Zr Hf Sm Eu Gd Ti Dy Y Er Yb Lu Sc V

  Figure13

Table 4

 4

	). In all diagrams,

  7: 143 Nd/ 144 Nd versus 87 Sr/ 86 Sr for clinopyroxene separates from Morocco, Jordan, and Cameroon. Data for DMM ( 143 Nd/ 144 Nd=0.51313, 87 Sr/ 86 Sr=0.70263), and BSE ( 143 Nd/ 144 Nd=0.512638, 87 Sr/ 86 Sr=0.7045) are from Workman and Hart (2005), and for HIMU ( 143 Nd/ 144 Nd=0.51285, 87 Sr/ 86 Sr=0.70285) from

Table 1 :

 1 Sample list, region, locality, rock type, modal composition, primary magmatic paragenesis, primary magmatic facies, subsolidus paragenesis and features, facies transitions, metasomatic paragenesis or features, late features and alteration phases, microtextures, average grain size, and estimated temperatures for the studied pyroxenites. Modal proportions are given in %, t indicates amounts as traces. FMC stands for French Massif Central.

Table 2 :

 2 Major element composition of minerals (in wt %). Same abbreviations as in Table

Table 3 :

 3 Trace element concentration for minerals (ppm). Same abbreviations as in Table1. n is the number of analyses that is averaged. ' and " on sample names indicates that different types of minerals are present. Underlined minerals have been analyzed at the IGG (Pavia), others at LMV (Clermont-Ferrand).

Table 4 :

 4 Major (wt %) and trace (ppm) element whole rock compositions. LN-78a and LN-78b represent two different domains of sample LN-78, and LN-78-avg the averaged value. bdl means below detection limit.

Table 5 :

 5 Isotopic composition of mineral separates. Same abbreviations as in Table1. For oxygen isotope composition, some samples have been duplicated. std err is the standard error on the measurement.For each sample, 1 to 2mg of separated grains were placed under a 25 W Merchantek CO 2 laser. The produced reaction triggers the oxidation of the different mineral molecules, and liberates the O 2 following reactions as 2MgO+SiO 2 +xF 2 2MgF 2 +SiF 4 +2O 2 +(x-4)F 2 (with a large x in order to achieve a high total yield). The gas mixture was injected in a separation line in which different cold trap and heated salts (KCl at ~140°C) allow us to trap all the molecules but O 2 . The purified O 2 is thereafter injected in a mass spectrometer (Finnigan MAT Delta plus XP) to analyze the different isotopes. A laboratory inner reference gas is jointly analyzed to compare the analyzed sample with the V-SMOW international standard.

	The δ 18 O value is then calculated (with δ 18 O‰	=	ë ê ê ê é	O 16 16 / O O/ 18 18	(V ( O	SMOW) ) sample -	-	1 ú ú û ù	ú	1000

  La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

	.8 % MgO 0.5126 0.5138 0.5134 0.5130 δ 18 O Orthopyroxene Cpx Grt Amp rich-part Spl Rock/Chondrites Opx Ol B SE FMC Morocco Regional mantle This study Jordan a M orocco LN-78 LP-27 SD-53 Le Pouget TAK-3 TAK-4 C am eroon DMM HIMU 143 Mantle Cpx Mantle array N d/ 144 N d	7.8 % MgO 0.5126 Cameroon 100 b 0.5138 YK-01 YK-03 YK-05 YK-12 Cpx 0.5134 YK-13 YK-16 143 N d/ 0.5130 144 N d δ 18 O Spinel Grt Jordan Spl Rock/Chondrites M o ro c c o F M C J o rda n C a me ro o n Opx Magmatic Grt prim. MORB prim. alk. bas. B SE Regional lavas This study Jordan M orocco Jo-7b C am eroon Jo-7h Jo-10e Jo-12h HIMU Mantle Gt DMM
	1	Cpx 0.703 87 S r/ 5.5 86 S r 5.3 δ 18 O Clinopyroxene (‰ SMOW), n=18 0.5122 0.701 0.702 0.704 0.705 0.706 5.1 4.9 4.7 6.1 5.9 5.7	1 10	0.5122 0.701 δ 18 O Garnet (‰ SMOW), n=12 0.702 0.703 0.704 0.705 5.5 5.3 5.1 4.9 4.7 6.1 5.9 5.7 0.706 87 S r/ 86 S r
	.1	7.8 % MgO	France et al., Fig. 7 .1 a France et al., Fig. 8	Cpx	b
		Grt Rock/Chondrites	Spl	Opx			100	Ol Rock/Chondrites Spl	Grt	Opx
							10
	1						1
		Ol						Spl	Ol
	.1			Spl	c		.1	d
		Rock/Chondrites					100	Rock/Chondrites
		Opx						Opx
		Cpx	Grt	Pl			10	Grt	Cpx	Pl
	1						1
	.1				e		.1	f
								BaRbTh U NbTa LaCePr SrNd Zr HfSmEuGdTbDyHo Y ErTmYbLu

France et al., Fig. 6

Acknowledgments

We express our warm thanks to the various people involved at different technical stages of this work: C. Bosq, and D. Auclair-Aubierge for assistance during sample preparation, and Garnet Pyroxenites in Old Orogenic Regions TIMS measurements; J.L. Devidal for assistance during EPMA measurements; and J.L. Piro for assistance during LA-ICP-MS measurements. H. Downes, M. Wilson, and B. Ildefonse are thanked for useful comments on an early version of the manuscript. Two anonymous reviewers, Guilio Borghini, and the associate Editor are thanked for their constructive comments that have helped to largely improve the manuscript. C. Cordier is thanked for valuable discussions, and for her help for illustrations. We also thank J.C. Vilminot and D. Velde, who provided us garnet pyroxenite samples from the Devès Massif, together with related valuable geochemical data, J.P. Lorand for providing us Le Pouget sample from the MNHN-Paris collection, and R. Temdjim who shares the Cameroon samples property with P.

Boivin. This is CRPG contribution n°XXXX.

Garnet Pyroxenites in Old Orogenic Regions

Supplementary material:

Figure S1: a) Oxygen isotope fractionation between Grt and Cpx. For reference, the Δ 18 O=0 line is shown (continuous line). The dashed line corresponds to fractionation at 900°C calculated using the fractionation factors of [START_REF] Zheng | Calculation of oxygen isotope fractionation in anhydrous silicate minerals[END_REF]. b) Oxygen isotope fractionation between Opx and Cpx. For reference, is shown the Δ 18 O=0 line (continuous line), and the field for lherzolites from Yemen [START_REF] Chazot | Oxygen isotopic composition of hydrous and anhydrous mantle peridotites[END_REF]. Cpx and Grt oxygen isotopic compositions are positively correlated and plot below the line corresponding to  Cpx-Grt = -0.4‰, indicating that these minerals have been equilibrated to T above 900° C, in agreement with T calculated using their chemical composition (see section 8. 1.2.). Three samples from Cameroon (YK-01, YK-03, and YK-05) have positive  Cpx-Grt values and record slight O-isotope disequilibrium.

 Cpx-Opx values are negative for all but two samples; the values are heterogeneous but always above  Cpx-Opx =-0.8‰.

Table S1:

Redox calculations results.

Analytical techniques

This study is based on analyses of whole rocks, and minerals that have been separated under binocular microscope for their purity after crushing, sieving and washing. In-situ analyses have been made on polished thin sections (30, 100 or 150 µm thick).

Major element mineral compositions were determined using the Cameca SX100 electron Whole rock major and trace element concentrations have been determined by a lithium metaborate fusion method and using an ICP-AES and an ICP-MS, respectively at the Activation Laboratories (Ontario). For sample from "Le Pouget" (FMC), the available sample amount was very small and the whole rock trace element content has been estimated using the mineral trace element compositions, and the modal proportions.

The oxygen isotopic composition of mineral separates was analyzed at the CNR-IGG of Pisa (Italy), by conventional laser fluorination, reacting the samples under a F 2 gas atmosphere.