Petrology of ultrabasic and basic xenoliths from the Kerguelen Islands. The mineralogical and thermobarometric constraints and their geodynamical implications.

• Main Author: Grégoire, Michel
• Other Authors: Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), Université de Saint Etienne, Jean-Yves Cottin, André Giret
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 1994
• Subjects: Kerguelen Islands; Indian Ocean; Petrology; Magmatism; UB-B xenoliths; Harzburgites; Dunites; Oceanic granulites; Sapphirine; Cumulates; Mantle-magmas interaction; underplating; Iles Kerguelen; Océan Indien; Pétrologie; Magmatisme; Enclaves UB-B; Granulites océaniques; Saphirine; Cumulats; Interactions manteau-magmas; sous-placage; [SDU.STU.PE]Sciences of the Universe [physics]/Earth Sciences/Petrography; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry
• Online Access: https://theses.hal.science/tel-01293475; https://theses.hal.science/tel-01293475/document; https://theses.hal.science/tel-01293475/file/theseMGregoire1994.pdf

The Southeast province of the Kerguelen Islands display several localities of ultrabasic-basic xenoliths (UB-B) that were entrained by highly alkaline lavas. Except Eclogitic, all known types of xenoliths from continental and oceanic areas are represented. This variety has led to a hierarchical typology by textural criteria (first order) and mineralogical criteria (second order). Three types and seven subtypes are defined. Type I is characterized by textures of mantle tectonics: it has subtypes I (harzburgites) and I (dunite). Type II, metamorphic textures with relics of igneous textures, contains IIa subtypes (cpx + opx + sp), IIb (cpx + ilm + sp) and IIc (lmenite-bearing metagabbros). Type III has typical magmatic textures and book consist of subtypes hornblenditic and biotitic.Types I and II have been the subject of further study as type III. Type I xenoliths are witnesses of the upper mantle and have been equilibrated in the “spine peridotite” stability field. They reflect a competition between several mantle processes: partial melting, metasomatism and mantle-melts interaction. One of the two types of harzburgites contains clinopyroxene demonstrating very clearly mantle-melts interaction. The same mechanism plays a key role in the genesis of dunite and associated composite xenoliths. Type II xenoliths are originally magmatic cumulates and segregates. The type IIa form a complete suite, from ultramafic terms (peridotites) to basic terms (metagabbros) and could be connected to the tholeiitic-transitional magmatism of the archipelago. Several reactions (symplectites, coronites) are observed and some produce associations of saphirine +/- garnet. These rocks have been equilibrated in the conditions of the granulite facies at 0.5 to 1.6 GPa and 900 to 1000 ° C. The type IIb corresponds to deep segregates of alkaline magmas in emplaced within the upper mantle (0.7 to 1.35 GPa, 850-1000 ° C). The type IIC form a homogeneous suite, close to the compositions of the tholeiitic-transitional liquids occurring at the ...