Structure and composition of the subcontinental lithospheric mantle beneath the Sangilen Plateau (Tuva, southern Siberia, Russia): evidence from lamprophyre-hosted spinel peridotite xenoliths

We present new data on spinel peridotite xenoliths hosted in Agardag alkaline lamprophyres from the Sangilen Plateau (Tuva, South Siberia, Russia), sampling at similar to 450 Ma the subcontinental lithospheric mantle of the Tuva-Mongolian micro-continent that belongs to the accretionary Central Asian orogenic belt at the southern edge of the Siberian craton. Xenoliths are spinel lherzolites principally showing poikilitic and subordinately coarse granular and coarse equigranular textures. Geothermobarometric calculations for pyroxene yield a narrow range of equilibration temperature (ca. 1000-1100 degrees C) that corresponds to lithospheric depths from 43 to 53 km (1.3-1.6 GPa) along a hot intracontinental geotherm. Variation of mean Mg# [100*Mg/(Mg + Fe)] of olivine (87.9-90.9) with mean Cr# [100*Cr/(Cr + Al)] of spinel (9.5-45.7) indicates that spinel lherzolites are mostly residues of up to 10% melting of a fertile peridotite source. In terms of normalized REE (Rare Earth Element) and incompatible trace element patterns of clinopyroxene, the Sangilen xenoliths can be classified into three types: Type I characterized by convex-upward REE patterns depleted in LREE (0.10