Geochronology and Geochemistry of the Xingxingxia Triassic A‐type Granites in Central Tianshan, NW China: Petrogenesis and Tectonic Implications

Abstract

The Triassic granitoids in Central Tianshan play a key role in determining their petrogenesis and tectonic evolution on the southern margin of the Central Asian Orogenic Belt. In this study, we have presented SHRIMP zircon U–Pb ages, Hf isotopic, and geochemical findings on the Xingxingxia biotite granite, amazonite granite, and granitic pegmatite in Central Tianshan, NW China. Zircon U–Pb dating yielded the formation ages of 242 Ma for the biotite granite and 240 Ma for the amazonite granite. These granitoid rocks have high K2O and low MgO and CaO contents. They are enriched in Nb, Ta, Hf, and Y, and depleted in Ba and Sr, showing flat HREE patterns and negative Eu anomalies. They have typical A‐type granite geochemical signatures with high Ga/Al (8–13) and FeOT/(FeOT+MgO) ratios, showing an A2 affinity for biotite granite and an A1 affinity for amazonite granite and granitic pegmatite. Zircon ɛHf(t) values of the granitoids are 0.45–2.66 with Hf model ages of 0.99–1.17 Ga. This suggest that these A‐type granites originated from partial melting of the lower crust. We proposed that Xingxingxia Triassic A‐type granites formed under lithospheric extension from post‐orogenic to anorogenic intraplate settings and NE‐trending regional strike‐slip fault‐controlled magma emplacement in upper crust.