Time constraint on the closing of the Paleo-Asian Ocean in northern Beishan of Inner Mongolia: Evidence from Heihongshan admellite

The Late Carboniferous admellite in the Heihongshan area is located in the northern part of the Hongshishan-Baiheshan-Pengboshan ophiolite belt. The geochemical characteristics show that the admellite belongs to metaluminous to weakly peralic potassium aluminous calc alkaline series I type granite of high differentiation; its LREE enrichment and LREE and HREE fractionation are obvious, with weak Eu negative anomaly and right-inclined rare earth curve. Trace elements are relatively enriched in Ba, K, Zr and Hf but depleted in Nb, Ti, P and Sr, indicating the characteristics of intrusive rocks related to subduction and formed in the volcanic arc environment before collision. The U-Pb dating of LA-ICP-MS zircon yielded weighted average ²⁰⁶Pb/²³⁸U age of 315.2±2.5Ma. Comprehensive studies show that the Heihongshan area belonged to the volcanic arcs on the active continental margin in the Late Carboniferous epoch, and the Hongshishan-Baiheshan-Pengboshan ophiolite belt suggests that the oceanic basin in Heihongshan area was closed in the Late Carboniferous epoch.