东昆仑东段东昆中构造混杂岩带长石山蛇绿岩年代学、地球化学特征及其构造意义

Age, geochemical characteristics and tectonic significance of Changshishan ophiolite in central East Kunlun tectonic mélange belt along the east section of East Kunlun Mountains

东昆仑东段东昆中构造混杂岩带长石山地区新发现一套蛇绿岩,主要由蛇纹岩、辉长岩、辉绿岩、玄武岩、含泥碳硅质岩组成。通过对蛇绿岩中辉长岩进行LA-ICP-MS锆石U-Pb同位素研究,获得年龄为(537.2±3.5)Ma,表明蛇绿岩形成于早寒武世。岩石地球化学研究显示,蛇纹岩的原岩为橄榄岩类,稀土元素配分曲线具开阔U型特征;辉长岩发育明显的堆晶结构,具不同程度的Eu正异常,轻稀土较重稀土富集,但稀土总量较低;玄武岩轻稀土相对重稀土富集,富集大离子亲石元素,高场强元素不分异,Nb轻微亏损,具E-MORB与IAB的双重特征。长石山蛇绿岩形成于弧后盆地环境,指示布青山—阿尼玛卿原特提斯洋在早寒武世((537.2±3.5)Ma)前已经开始向北俯冲,并在东昆中地区拉张形成弧后盆地。

The ophiolite in central East Kunlun tectonic mélange belt along the east section of East Kunlun Mountains is mainly composed of serpentines, gabbro, diabase, basalt and peat siliceous rock. The LA- ICP- MS zircon U- Pb dating of the gabbro in ophiolite shows that the age is(537.2 ± 3.5) Ma, which indicates that the ophiolite was formed in the Early Cambrian. Detailed petrogeochemical studies show that the protolith of serpentines is peridotite and the rare earth element distribution curve has wide U-type characteristics. The gabbro displays obvious accumulate texture with varying degrees of Eu anomalies. The light rare earthis relatively high but the total rare earth is low. The light rare earth of basalt is relatively higher than heavy rare earth. And it shows systematic enrichment of LILE, no differences of HFSE and slight depletion of Nb and it also has double features of E-MORB and IAB. The ophiolite originated in back-arc basin which had been formed by the subduction of Proto-Tethys Ocean in BuqingshanAnyemaqen before the Early Cambrian and then eventually formed a basin in East Kunlun region after extension.