青海尕林格南地区火山岩地球化学特征及锆石U-Pb年龄

在东昆仑山脉西段祁漫塔格山中东部的尕林格南地区发育一套火山岩,调查显示火山活动爆发相→溢流相相间的韵律周期较明显,见由玄武质含火山角砾凝灰岩→玄武岩、玄武质凝灰岩→安山岩、安山质角砾凝灰岩→安山岩,以及安山质含火山角砾凝灰岩和安山岩质凝灰岩→玄武岩组成的4个韵律。根据研究区安山质火山角砾凝灰岩的LA-ICP-MS锆石U-Pb年龄222.2±2.1Ma,将该火山岩地层由前人划分的顶志留统—下泥盆统契盖苏组火山岩段重新厘定为上三叠统鄂拉山组。岩石地球化学研究结果表明,该套火山岩属于亚碱性钙碱性系列岩石,具有富钾、同源岩浆演化的特点,并具弧火山岩和碰撞火山岩的地球化学特征,为陆内造山作用下的产物,较好地记录了东昆仑祁漫塔格造山带在晚三叠世岩浆演化的地质信息。

Geochemistry and zircon U-Pb ages of the volcanic rocks in southern Galinge, Qinghai Province

Volcanic rocks are well developed in southern Galinge which lies in mid-eastern Qimantag Mountain of the western part of the East Kunlun Mountains. The investigation shows that the volcanic activity from explosive phase to overflow phase is more pronounced and there are four rhythms at most. According to the zircon U-Pb age (222.2±2.1Ma) obtained by the LA-ICPMS for the tuff in the study area, the volcanic rocks should be assigned to Late Triassic (T₃e) rather than to volcanic rocks of top Silu-rian-Early Devonian Qigaisu Formation (S₄D₁q¹) assigned by previous researchers. Geochemical studies of the rocks show that the volcanic rocks are of sub-alkaline-calc-alkaline series rich in potassium and characterized by cognate magma evolution, and have the geochemical features of arc rocks and collisional volcanic rocks. They are the products of intracontinental orogenesis, and hence the geological information of magmatic evolution of the East Kunlun Qimantag orogenic belt in the Late Triassic period is well doc-umented.