Pyroxenite-derived Cenozoic basaltic magmatism in central Inner Mongolia, eastern China: Potential contributions from the subduction of the Paleo-Pacific and Paleo-Asian oceanic slabs in the Mantle Transition Zone

Abstract

Widespread Cenozoic basalts, erupted at ca. 24–0.16 Ma in central Inner Mongolia, eastern China, are significant for understanding the potential links between deep subduction of oceanic slabs and the genesis of continental intra-plate magmatism. Here we examine the whole-rock geochemical and isotopic data, as well as olivine compositions, for Cenozoic alkali and tholeiitic basalts from the Abaga, Huitengliang, and Chifeng areas in central Inner Mongolia. The results suggest that fractional crystallization of olivine + clinopyroxene (in the alkali basalts) and olivine (in the tholeiites), played a key role in their magmatic evolution, without significant crustal contamination or post-magmatic alteration. Geochemical and petrogenetic analyses show that pyroxene and garnet were dominant phases in the residual mineral assemblage for both alkali basalts and tholeiites, implying a pyroxenite source for these basalts. We propose that a pyroxenite-dominated source may be the product of reaction between recycled oceanic slab-derived melts and surrounding mantle peridotites. The spatial and geochemical variations of the Cenozoic basalts in central Inner Mongolia, together with recent geophysical and geological observations in eastern China, imply that the origin and evolution of large-scale Cenozoic continental intra-plate magmatism can be related to subduction of the Paleo-Pacific and Paleo-Asian oceanic slabs. Incorporation of recycled oceanic materials from these two subducted slabs thus influenced the mantle source lithologies and deep-Earth geodynamic processes beneath eastern China.