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 surface of the Islands, and equilibrated within the conditions of the granulite facies.A discussion integrating these features to geochronology and geophysical data confirm and explain the inferred crustal thickening highlighted by the evolution of the seismic velocities at depth. The north end of the Kerguelen Plateau was built at the junction between the India / Antarctica ridge and the Australia / Antarctica ridge between 56 and 43 Ma. Near the Moho abundant tholeiitic-transitional magmas, produced by the synergy the the young East Indian Ridge and the Kerguelen plume, have formed cumulates and segregates that were "underplated" and that largely contributed to the crustal thickening. This is then amplified by the volcanic overload related to the duration of the plume activity, the cumulates slowly cool and sink to depths corresponding to the granulite facies. The younger alkaline magmas sampled those deep rocks and uplifted them to the surface.This crustal thickening, and some special characterisitcs of the magmatic complexes from the archipelago, allows to consider an abnormally low density of the lithosphere and, consequently, to propose that it could not be easely subducted. In that case, Kerguelen would be a continental protolith.

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   |wiki=    Wicri/Asie
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   |clé=     Hal:tel-01293475
   |texte=   Petrology of ultrabasic and basic xenoliths from the Kerguelen Islands. The mineralogical and thermobarometric constraints and their geodynamical implications.
}}