Late Mesozoic Eastern Mongolia Volcanic Area: Structure, Magmatic Associations, and Sources of Melts

Abstract

The Eastern Mongolia Volcanic Area (EMVA) is the largest Late Mesozoic intracontinental volcanic area of East Asia. Its magmatic activity lasted from ~ 170 Ma to the beginning of Cenozoic, but the peak of activity occurred between 135 and 105 Ma. It was accompanied by rifting and formation of NE-trending grabens and troughs filled with thick volcanic sequence. The largest volcanic eruptions occurred in the first half of the Early Cretaceous. They were mainly represented by mafic lavas and were terminated by acid volcanism. The second half of the Early Cretaceous was marked by exclusively mafic volcanism, which was replaced by alkaline basaltic rocks since the end of the Early Cretaceous and in the Late Cretaceous. The mafic rocks of the EMVA are trachybasalt and basaltic trachyandesite, with subordinate alkaline basaltic rocks. The geochemical characteristics of these rocks indicate that they were derived from two magma types related to different mantle sources: (1) suprasubduction basalts (IAB) and (2) within-plate ocean-island basalts (OIB). The predominance of rocks with transitional characteristics testifies the interaction of magmas or their sources during their formation. The widest spread OIB-type rocks have (Th/Nb)PM ≤ 1. The IAB-type mafic rocks are of limited distribution and were formed mainly at the early stages of the EMVA evolution. The felsic igneous rocks of the EMVA were mainly derived by crustal anatexis, as well as by the interaction of anatectic melts with basaltic derivatives. A model is proposed, in which the EMVA was formed in a composite geodynamic setting, which was determined by the mantle plume impact on the active continental margin. The magmatic evolution is thought to be related to the interaction of plume-derived magmas with a subduction-modified mantle wedge.