Compositional heterogeneity of the continental mantle: evidence from ultramafic xenoliths in Cenozoic basalts from northern Eurasia

Abstract

A representative collection of spinel lherzolite xenoliths in Cenozoic basalts from the Baikal Rift (Khamar-Daban Range, Vitim Plateau, and Udokan Plateau), Tien Shan, Bohemian Massif, Pannonian Basin, Catalonia, central and southeastern Spain, Canary Islands, and Lanzarote Island was studied to compare the chemical and isotopic-geochemical composition of the mantle beneath these territories. Comparison of the He signatures, considered together with data on the whole-rock compositions and REE patterns of the samples, reveals variable degrees of lherzolite mantle depletion due to both its original composition and variations in the degree of its partial melting. Another real process is mixing of two reservoirs caused by mantle convection, for example, mixing of a plume component plus subducted lithosphere material. Chemical geodynamics offers various variants of mixing based on studying the isotopic composition not only of the He--Ar and Nd--Sr systems but also of the Pb, Hf, and Os, although realistic implications for chemical geodynamics can be obtained only from the former two systems.