HOLOCENE VOLCANISM IN CENTRAL MONGOLIA AND NORTHEAST CHINA: ASYNCHRONOUS DECOMPRESSIONAL AND FLUID MELTING OF THE MANTLE

Abstract

Volcanic eruptions in central Mongolia during the latest Pleistocene and Holocene time preceded an initial Holocene volcanic event of 8740 ± 400 years ago in Northeast China and terminated simultaneously with that event as inferred from 14C datings. Alkali basaltoid magmatic material from a partially melted (1.5–3%) mantle source was erupted in the Taryat Basin of central Mongolia, at first along a nearly east-west line of volcanoes, and afterwards material of higher melting (up to 5%) was discharged along the north-northeast line of Khorgo edifices. A material of similar composition was erupted in the Jingpohu area, Northeast China during the period from 5430–4400 BP. Initial liquids of ∼2% beneath the Frog Pool volcanic center and ∼5% beneath Crater Forest were expressed varying liquids beneath the latter area, yielding final melts of ∼5%. The action of the decompressional and the fluid mechanism was followed by in eruptions of, respectively, isotope-homogeneous magmas in central Mongolia and isotope-heterogeneous magmas depleted in high field strength elements (Nb, Ta, Ti) in Northeast China.