Ages and geochemistry of the Erbeng granite in southern Tianshan orogenic belt, Xinjiang: New constraints on the tectonic evolution of the southern Tianshan Ocean

Erbeng plutons are located along the South Tianshan Late Paleozoic intrusive rock belts. LA-ICP-MS dating yielded a zir-con U-Pb age of 296.1±1.8Ma(MSWD=0.05), suggesting that this body was emplaced in the Early Permian. The granites from the Erbeng plutons are characterized by silica(66.96%~67.3%) and rich alkali(Na₂O+K₂O=7.53%~7.97%), obvious variation of K₂O/Na₂O(1.15~1.27) with the A/CNK being 0.99~1.03, suggesting that they are of weakly peraluminous and high-K calc-alkaline series. They are enriched in LREE((La/Yb)_N=27.03~30.62) and depleted in HREE((LREE/HREE)=18.2~20.1). They have negative Eu anomaly(δEu=0.64~0.68), with slightly right-dipping V-type chondrite-normalized rare earth element patterns. Geochemical-ly, they show transition features from I to A type granites. This age, together with their geochemical signatures of I-A type granite and the zircon saturation temperatures of 819~837℃, indicates that this body was emplaced at a transition stage from syncollision to post-collision. From the zircon U-Pb ages combined with regional geological background, the authors infer that the southern Tian-shan Ocean might have been closed at least before the beginning of the Early Permian.