藏南洛扎地区过铝质花岗岩的地球化学特征及构造背景

Geochemical features and tectonic setting of peraluminous granite in the Lhozag area,southern Tibet

洛扎及其以南地区分布有规模不等、产状不同的过铝质二云母(白云母)二长花岗岩和电气石二长花岗岩,这些岩体侵位的时代为中新世,构成了高喜马拉雅花岗岩带的东延部分。岩体以高铝、低镁铁组分,高锶、氧同位素比值为特征,地球化学研究显示它们是泥质岩的深熔作用和岩浆的结晶分异作用所形成的产物。过铝质花岗岩是在后碰撞造山作用阶段的大规模伸展拆离作用背景下沿拆离构造带侵位的,形成于藏南拆离系韧性活动阶段的晚期,是一种典型的后碰撞过铝质花岗岩。

Peraluminous two-mica(muscovite)monzogranite and tourmaline monzogranite of varying size and occurrence are distributed in Lhozag and areas to its south.These rock bodies were em placed in the Miocene and constitute the eastward extension of the Higher Himalaya granite belt.They are characterized by the high-Al and low-Fe and-Mg composition and high Sr and O isotope ratios.Geochemical study shows that they are the product of anatexis of argillaceous rocks and fractional crystallization of magmas.Peraluminous granite was emplaced along a detachment zone in the setting of larger-scale extensional de-tachment in the stage of post-collisional orogeny.The peraluminous granite formed in the late stage of ductile activity of the southern Tibetan detachment system.It is a typical post-collisional peraluminous gran-ite.