The lithosphere beneath the Sangilen Plateau, Siberia: evidence from peridotite, pyroxenite and gabbro xenoliths from alkaline basalts

摘要: Ultramafic and mafic xenoliths in Ordovician Agardag alkaline basalt dikes from the Sangilen Plateau, southeastern Siberia, provide samples upper mantle crust beneath central Asia. Three major groups were distinguished among xenoliths: Group I are spinel lherzolites, II spinel-garnet clinopyroxenites, III comprises gabbroic with two subgroups: IIIa garnet bearing gabbroids IIIb is represented by garnet-free gabbroids. The lherzolite represent uppermost lithospheric Plateau have geochemical characteristics similar to those of primitive mantle. Spinel-garnet clinopyroxenite igneous origin fragments intrusive bodies crystallized at depths close mantle-crust boundary, as well lower crust. evidently crystallization products melts trace element composition parental magma Bashkymugur gabbronorite-monzodiorite intrusion. Gabbroic demonstrate presence intermediate magmatic chambers within during Early Palaeozoic. relatively high equilibration temperatures largely attributable a plume occurring Ordovician.