东昆仑印支晚期幔源岩浆活动

Late Indosinian mantle-derived magmatism in the East Kunlun

东昆仑造山带印支晚期广泛发育一期幔源岩浆活动,其代表性岩石类型为角闪辉长岩、煌斑岩和辉绿岩。石灰沟外滩岩体是这类岩体中最大的一个,40Ar/39Ar同位素定年结果为220Ma左右,具有明显的结晶分异特征。根据地质学、岩石学与地球化学特征,岩浆起源于深度大于90km的上地幔源区,富含挥发分(H2O)的条件使橄榄石在部分熔融过程中更趋稳定,辉石和尖晶石组分更多地进入岩浆,从而制约了岩浆中高Cr低Ni的特点。幔源岩浆的广泛出现是该区软流圈-岩石圈系统对特提斯洋闭合的响应,是在加厚陆壳的底部幔源玄武质岩浆底侵作用的结果。

A phase of mantle-derived magmatism occurred extensively in the East Kunlun orogenic belt in the late Indosinian period.The typical rock types are hornblende gabbro,lamprophyre,and diabase.The Waitan rock body at Shihuigou is the largest one of the igneous rock bodies in the belt.It has a 40 Ar / 39 Ar age of ～220Ma and shows the distinct features of crystallization differentiation.According to the geologi-cal,petrological,and geochemical characteristics,the magma originated from the upper mantle source area at a depth of >90km.At the presence of abundant volatiles(H 2 O),olivine tended to be more stable dur-ing partial fusion and more pyroxene and spinel components entered the magma ,thus constraining the high-Cr and low-Ni characteristics.The extensive occurrence of the mantle-derived magma is believed to be a response of the asthenosphere-lithosphere system of the area to the closure of the Tethyan Ocean as well as the result of underplating of mantle-derived basaltic magma at the base of the thickened crust.