布青山蛇绿混杂岩带查汗额热格玄武岩地球化学特征与构造意义

Geochemical characteristics and tectonic implication of Chahanerege basaltin the Buqingshan Ophiolite Melange Belt

布青山蛇绿混杂岩带西端查汗额热格地区出露一套大洋板块玄武岩,主要由枕状玄武岩和球颗玄武岩组成,局部有块状玄武安山岩,且伴生有磁铁蛇纹岩和辉长岩,共同构成蛇绿岩带。为了解其岩石成因和形成的构造背景,对其进行了详细的岩石地球化学研究。研究表明:该套岩石属亚碱性系列,相对富集Rb、Ba、Sr等大离子亲石元素,相对亏损Nb、Zr、Th等高场强元素;稀土元素总量较低,且轻重稀土比值较小,球粒陨石标准化配分曲线呈微弱左倾;构造判别图则表明该玄武岩形成于洋中脊环境。综合前人研究成果,认为查汗额热格玄武岩形成于早石炭世—早二叠世,进一步表明东昆仑南缘地区存在晚古生代布青山-阿尼玛卿古特提斯洋分支洋盆。

There is a set of oceanic plate basalt at the west part of Buqingshan Ophiolite Melange Belt in the Chahanerege area,which mainly consists of pillow-shaped basalt,pellet basalt and a small amount of massive basaltic andesite in local.There are associated by magnetite ophiolite and gabbro in the Chahanerege area,which constitute the ophiolite belt together.In order to learn about the petrogenesis and tectonic setting,the study of petrography and petrogeochemistry is carried out.The result shows that the basalt belongs to the subalkali series,and is relatively enriched in large ion lithophile elements such as Rb,Ba,Sr,and relatively deficient in high field strength elements such as Nb,Zr,Th.The∑REE content is low,and the LREE and HREE fractionation is not obvious.The tectonic discriminant diagram shows that it is formed in the mid-ocean ridge environment.According to the previous research result,the mid-ocean ridge basalt is formed in the period of Early Carboniferous to Early Permian.It is further indicated that there is the branch ocean basin of Late Paleozoic Buqingshan-Animaqing Paleo-Tethys developed in the south margin of East Kunlun.