Find of ferropicrite and high-Mg andesite from the Devonian accretionary complex in the Hangay Mountains, Mongolia

Abstract

Many greenstone-chert bodies occur in the Devonian accretionary complex in the Hangay Mountains, Central Mongolia. Previous studies concluded that they are mostly alkali basalt of seamount origin. Our research in the Uyanga Village, however, reveals that the greenstones are mostly tholeiitic, ferrobasalt is also abundant, and alkali basalt does not occur. We also find ferropicrite. These facts indicate their origin in an oceanic LIP. The high-Mg andesite occurs as sills and resembles sanukite in respect to high Cr# of spinel and distinct negative anomaly of Nb. These HMA sills may represent forearc magmatism related to subduction of a young oceanic plate or a spreading axis after the formation of the accretionary complex.