The lithosphere beneath the Sangilen Plateau, Siberia: evidence from peridotite, pyroxenite and gabbro xenoliths from alkaline basalts |
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Authors: | V V Egorova N I Volkova R A Shelepaev A E Izokh |
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Institution: | (1) Institute of Geology and Mineralogy, Russian Academy of Sciences, Novosibirsk, Russia |
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Abstract: | Summary Ultramafic and mafic xenoliths in Ordovician Agardag alkaline basalt dikes from the Sangilen Plateau, southeastern Siberia,
provide samples from the upper mantle and crust beneath central Asia. Three major groups were distinguished among the xenoliths:
Group I xenoliths are spinel lherzolites, Group II xenoliths are spinel-garnet clinopyroxenites, and Group III comprises gabbroic
xenoliths with two subgroups: Group IIIa comprises garnet bearing gabbroids and Group IIIb is represented by garnet-free gabbroids.
The spinel lherzolite xenoliths represent the uppermost lithospheric mantle beneath the Sangilen Plateau and have geochemical
characteristics similar to those of primitive mantle. Spinel-garnet clinopyroxenite and gabbroic xenoliths are of igneous
origin and represent fragments of intrusive bodies crystallized at depths close to the mantle-crust boundary, as well as in
the lower and the upper crust. The gabbroic xenoliths are evidently the crystallization products of melts similar in major
and trace element composition to parental magma of the Bashkymugur gabbronorite-monzodiorite intrusion. Gabbroic xenoliths
from the Ordovician Agardag alkaline basalt dikes demonstrate the presence of intermediate magmatic chambers within the crust
beneath the Sangilen Plateau during the Early Palaeozoic. The relatively high equilibration temperatures of the mantle and
lower crust xenoliths in the Agardag alkaline basalt dikes are largely attributable to a plume occurring beneath the Sangilen
Plateau during the Ordovician. |
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