Constraining lithospheric removal and asthenospheric input to melts in Central Asia: A geochemical study of Triassic to Cretaceous magmatic rocks in the Gobi Altai (Mongolia)

By contrast, geochemical and isotope data from the youngest magmatic rocks in the area - 107-99 Ma old volcanic plugs from Tsost Magmatic Field - have OIB-like trace element patterns and are interpreted to have formed by low degrees of partial melting of a garnet-bearing lherzolite mantle source. These rocks did not undergo significant crustal contamination, and were derived from asthenospheric mantle. The evidence of a gradual shallowing of melting in the Gobi lava provinces, culminating in an asthenospheric source signature in the youngest magmatic rocks is similar to examples from neighboring China, emphasising the wide-scale effect of a regional Mesozoic magmatic event during similar time periods. We suggest that Mongolia underwent lithospheric thinning/delamination during the Mesozoic (between ~ 125 and ~ 107 Ma) with patchy areas thinning sufficiently to enable the generation of relatively small-scale asthenospheric-derived magmatism to predominate in the late Cretaceous.