Discovery of Late Devonian monzogranite from the Eastern Tianshan, and its constrains on the tectonic evolution of the Aqishan-Yamansu belt

The Aqishan-Yamansu belt, located at south of the Eastern Tianshan belt, is a pivotal part of the Central Asian orogenic belt.The most important feature of the Aqishan-Yamansu belt is the occurrence of voluminous igneous rocks, which mainly formed during Carboniferous and Permain with no pre-Carboniferous age has been reported.We present zircon LA-MC-ICP-MS U-Pb chronology of monzogranite, discovered on the southern margin of the Aqishan-Yamansu belt.The zircons from the monzogranite are mostly euhedral to subhedral, with oscillatory zoning and Th/U ratios more than 0.4, suggesting magmatic origin.Therefore, the obtained weighted mean ²⁰⁶Pb/²³⁸U age of 374.7±4.0 Ma (MSWD=0.7, n=17) can be used to represent the magma crystallization age.This result suggests that a magmatic event occurred during Late Devonian and formation of the Aqishan-Yamansu belt possibly began in Late Devonian at latest.Combined with the Late Devonian magmatism formed in arc environment in Central Tianshan, we concluded that the monzogranite may have been produced by the southward subduction of ancient oceanic plate beneath the Central Tianshan during Late Devonian.