Oceanic lithospheric mantle beneath the continental crust of the Chinese Altai

Abstract

Although subduction-accretion is proposed as a major regime in making new continental crust, how the lithospheric mantle forms remains unclear. Formed after the closure of the Palaeo-Asian Ocean, the Ashele basalt shows normal mid-ocean ridge basalt (N-MORB)-like characteristics with light REE-depleted patterns and extremely low contents of high field strength elements. The low Zr/Y and Nb/Y ratios of the basalt are significantly different from those of asthenosphere-derived melts, and the excess Eu and Sr suggest that the basalt was probably derived from accreted oceanic lithospheric mantle. The presence of the NMORB- like terrestrial basalt implies that subduction-accretion is an effective mechanism in building the refractory lithospheric mantle of Phanerozoic continents. © The Geological Society of London.