Geochemistry and tectonic settings of Indosinian granites in the Mayêr Kangri area, central Qiangtang, Tibet, China.

Abstract: Indosinian strongly peraluminous calc-alkaline granites (SP) are exposed in the Mayêr Kangri area, central Qiangtang, Tibet. They belong to S-type granites (CPGs), also called cordierite-bearing, biotite-rich peraluminous granites, which are different from muscovite-bearing peraluminous granites (MPGs) exposed extensively in southern Tibet. The geochemical characteristics of the granites are as follows: A/CNK>1; the corundum standard molecular mass fractions are all higher than 1.21%; K, Rb and Th are enriched and Sr, Ba and Ti are depleted; the chondrite-normalized REE distribution patterns show the slightly right-inclined "V"-shaped feature, with a relatively strong negative anomaly (δEu＝0.26-0.53, averaging 0.36). The CaO/Na2O ratios of the granites are <0.3, suggesting that the granites were derived from pelitic sources. The Al2O3/TiO2 ratios are <100, suggesting that the granites formed at high temperatures (≥875℃). In addition, the age of the SP granites is the same as that of blueschist and eclogite. During the late Indosinian collision between Gondwanaland and Eurasia, the underplating or injection of hot mantle-derived magmas led to dehydration-melting of pelitic source rocks, and finally the strongly peraluminous high-K calc-alkaline granites were formed.