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Featured researches published by M. Gregoire.


Lithos | 1996

Kerguelen basic and ultrabasic xenoliths: Evidence for long-lived Kerguelen hotspot activity

Nadine Mattielli; Dominique Weis; M. Gregoire; Jean Paul Mennessier; Jean-Yves Cottin; A Giret

Abstract The xenoliths from the Southeast Province of the Kerguelen Archipelago derived from the lower crust or the upper mantle, can contribute to define the characteristics of the mantle sources below Kerguelen and improve the constraints on the formation of the Kerguelen Islands and plateau. Our petrographic, geochemical and isotopic (Sr, Nd and Pb) study focuses on peridotites (Type Iα: harzburgite/clinopyroxene-poor Iherzolite and Type Iβ: dunite), 2-pyroxenes-spinel bearing ultrabasic and basic xenoliths [Type IIa: clinopyroxene-rich Iherzolite, wehrlite, (± olivine ± plagioclase) websterite, (± garnet ± sapphirine) metagabbro and anorthosite] and ilmenite metagabbros (Type IIc). The large ranges of isotopic ratios for the xenoliths reflect different degrees of interaction between a depleted MORB-type component, quite abundant in the Type II xenoliths, and the Kerguelen plume, distinctly predominant in the Type I xenoliths. Type I peridotites are residues of a previous partial melting event of the Kerguelen plume; residues that subsequently interacted with a percolating alkaline melt. 2-pyroxenes-spinel bearing ultrabasic and basic xenoliths (Type IIa) and ilmenite metagabbroic xenoliths (Type IIc) are deep cumulates crystallized from tholeiitic magmas. The isotopic results for the xenoliths strengthen the hypothesis of an oceanic origin for the Kerguelen Islands and refute the existence of pieces of old continental crust beneath the Islands and the northern part of the Kerguelen Plateau. They also confirm the importance of plume-spreading ridge interactions throughout the history of the Kerguelen plume. The isotopic and geochemical characteristics of the Type IIa and IIc xenoliths are consistent with the hypothesis of an Iceland-type setting for the northern part of the Kerguelen Plateau. The results for the Type I xenoliths on the other hand suggest a similarity between the Hawaii-type midplate volcanic structure and that of Kerguelen Islands. The isotopic data suggest that the Kerguelen xenoliths were formed recently (≤ 45 Ma), and thus support the hypothesis of the formation of the Plateau by the arrival of the plume at the base of the lithosphere (~ 115 Ma ago). The Plateau would have grown through several pulses of plume activity (~ 115, ~ 80, ~ 40 Ma), while the geotectonic environment changed with time (from a ridge-centered position to the present intraplate position). The occurrence of deep Type IIa and IIc xenoliths can explain the crustal thickening and provides evidence for the growth of oceanic plateaus by vertical accretion.


European Journal of Mineralogy | 2000

Incompatible trace element and isotopic (D/H) characteristics of amphibole- and phlogopite-bearing ultramafic to mafic xenoliths from Kerguelen Islands (TAAF, South Indian Ocean)

Bertrand Moine; Jean-Yves Cottin; Simon M.F. Sheppard; M. Gregoire; Suzanne Y. O'Reilly; A Giret

Alkali basalts from the Kerguelen Islands have entrained numerous phlogopite- and amphibole-bearing ultramafic to mafic xenoliths. These are subdivided into mantle harzburgites, dunites and associated composite xenoliths that represent mantle wall-rock (Type-I) and high pressure (10–15 kbar) segregates (Type II). A lamprophyric dyke containing phlogopite megacrysts has been also studied. Chemical compositions of amphiboles and phlogopites from both xenolith types are similar to those recognized in many ultramafic and mafic volatile-bearing xenoliths from kimberlites and alkali basalts and in peridotites and pyroxenites from orogenic lherzolite massifs. Interstitial amphibole and phlogopite in harzburgites and dunites probably formed during diffuse percolation of highly alkaline basic silicate melt within the upper mantle (porous flow). Evidence from composite xenoliths suggest that similar mantle melts migrated through a network of dykes generated by hydraulic fracturing in the Kerguelen upper mantle. The lamprophyre is the surface expression of this highly alkaline magmatic activity. The δD values of −92 to −61‰ SMOW for mica and amphibole of Type I and Type II xenoliths and of the phlogopite megacrysts are within the accepted mantle range. Calculated δD-H 2 O values in equilibrium with amphiboles and micas have a bimodal distribution (- 65 ± 5‰ and −83 ± 5‰) indicating that the percolating fluids were isotopically heterogeneous. The ubiquity of the highly alkaline magmatic activity is probably related to the late intraplate activity of the Kerguelen mantle plume.


European Journal of Mineralogy | 2009

Origin of rare earth element variations in clinopyroxene from plutonic and associated volcanic rocks from the Fouldé basin, Northern Kédougou inlier, Sénégal, West Africa

Edmond Dioh; Didier Béziat; M. Gregoire; Pierre Debat

Abstract: The Paleoproterozoic basin of Foulde´, in the northern part of the Ke´dougou inlier (eastern Se´ne´gal), comprises bothvolcanic and plutonic suites belonging to the same K-rich calc-alkaline series. Plutonic and volcanic rocks are coeval and they showstrong compositional similarities in major and trace elements including rare earths (REE). Clinopyroxene is ubiquitous in the maficrocks and has the same major-element (except CaO) and trace-element (except LREE, Th and U) contents in both suites. Theclinopyroxenefoundinbasaltsandbasalticandesiteshasconvexupwardchondrite-normalizedREEpatterns,withaLREEdepletion[(Ce/Yb) N ¼0.64–0.67)].Clinopyroxenefromgabbroshaschondrite-normalizedREEpatternscharacterizedbyaLREEenrichmentwith(Ce/Yb) N ¼1.86–1.66.Thesedifferencesarerelatedtotheemplacementmodeofthetwomagmaticsuites,i.e.tothecoolingrateof the magma. In volcanic rocks, very rapid cooling allows clinopyroxene to retain its primary magmatic composition. In plutonicrocks the lowercooling rate allows late-crystallization andsubsolidus processes, which modify the early trace-element composition.Themagmaticprocessesaffectingthemonzogabbrosareoftwotypes:(i)reactionbetweenthemainigneousphases(clinopyroxeneand plagioclase) and an interstitial melt crystallizing quartz and K-feldspar, and (ii) exsolutions of amphibole, ilmenite andorthopyroxene in the clinopyroxene. The core of monzogabbros clinopyroxene that shows no exsolution has a higher CaO contentthanthatofclinopyroxeneinthevolcanicrocks.WeproposethatexsolutionofCa-and-LREEdepletedorthopyroxeneintheinnerrimofthe clinopyroxeneinmonzogabbrosinduces anincrease oftheCa content ofitscore andmay explain itscompositionaldifference(Ca and LREE) with the clinopyroxene in volcanic rocks.Key-words: clinopyroxene, in situ trace elements, monzogabbros, basalts, exsolution texture, Paleoproterozoic, Se´ne´gal.


Nature | 1994

Oceanic mafic Granulite xenoliths from the Kerguelen Archipelago

M. Gregoire; Nadine Mattielli; C Nicollet; Jean-Yves Cottin; H Leyrit; Dominique Weis; N. Shimizu; A Giret


European Journal of Mineralogy | 1997

Xenoliths evidence for a refractory oceanic mantle percolated by basaltic melts beneath the Kerguelen Archipelago

M. Gregoire; Jean-Pierre Lorand; Jean-Yves Cottin; A Giret; Nadine Mattielli; Dominique Weis


Lithos | 2015

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

Gilles Chazot; Jacques Kornprobst; Luigi Dallai; Riccardo Vannucci; M. Gregoire; Hervé Bertrand; Pierre Boivin


Comptes Rendus Geoscience | 2002

Les xénolites ultramafiques du volcanisme alcalin quaternaire d'Oranie (Tell, Algérie occidentale), témoins d'une lithosphère cisaillée et enrichie

Mohamed Zerka; Jean-Yves Cottin; M. Gregoire; Jean-Pierre Lorand; M'Hamed Megartsi; Mohamed Midoun


Journal of Conference abstracts | 1996

Petrology of Kerguelen mantle xenoliths: Evidence of a strongly refractory oceanic mantle percolated by basaltic melts

M. Gregoire; Jean-Pierre Lorand; Jean-Yves Cottin; A Giret; Nadine Mattielli; Dominique Weis


Terra Antartica | 1995

The Kerguelen Archipelago: an hypothetic continental mafic protolith

M. Gregoire; Jean-Yves Cottin; Nadine Mattielli; C Nicollet; Dominique Weis; A Giret


VII Int. Symp. Antarctic Earth Sciences | 1995

The Kerguelen Archipelago: a Hypothetic Continental Mafic Protolith

M. Gregoire; Jean-Yves Cottin; A Giret; Nadine Mattielli; C Nicollet; Dominique Weis

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A Giret

Jean Monnet University

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Nadine Mattielli

Université libre de Bruxelles

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Dominique Weis

University of British Columbia

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Jean-Pierre Lorand

Centre national de la recherche scientifique

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