The petrochemistry characteristics and petrogenesis of peraluminous granite in Tibet

There are 61 major peraluminous granitic bodies in Tibet (TPGs) along the south of the Bangong Co-Gêrzê-Amdo-Nujiang suture, whose lithology includes tourmaline granite, muscovite granite and two-mica granite. The TPGs have SiO₂ = 65.7%−79.52%, K₂O + Na₂O = 2.20%−12.51%, K₂O/Na₂O = 0.49−1.04 and A/CNK = 1.04−1.38. Al₂O₃ gradually decreases and the other oxides disperse with the increase in SiO₂. The rock series is mainly calc-alk series with high potassium. It has typical characteristics of strongly peraluminous granite. Based on the aluminum saturation index and QAP plots, the peraluminous granite plot is mostly within the continental collision granite (CCG) field, indicating that the peraluminous granites in Tibet formed in a continental collisional setting. Ab-Or-Q-H₂O phase diagram indicates the pressure of 0.5 × 10⁸−2 × 10⁸ Pa in TPGs, from which it can be deduced that the forming temperature was under 700°C. The TPGs mainly occurred at the collision stage between two continental crust plates, and the original magma is rooted in the remelting from the upper crust. It is the S-type granite in petrogenesis. The South Gandise belt and the Lhagoi Kangri belt have similar characteristics, suggesting that the two belts have the same magma source and the same tectonic setting. Translated from Acta Geologica Sinica, 2006, 80(9): 1329–1341 [译自: 地质学报]