新疆西昆仑库地混杂带中基性火山岩构造环境分析

Tectonic settings of the basic igneous rocks in the Kudi ophiolite zone of West Kunlun Mountains, Xingjiang Province.

库地北一些克沟基性火山岩是西昆仑库地蛇绿岩的重要组成单元之一,而有关其形成的构造环境仍存在很多争议,由此影响了对该蛇绿岩性质、形成和演化方面的深入认识。笔者在野外对一些克沟基性火山岩地质剖面进行了详细的观察,在综合前人研究资料的基础上,利用地球化学(主量、微量及稀土元素)及Sm/Nd同位素分析等数据对其构造背景进行了多种手段相结合的判别和分析,确定其形成的构造环境为洋内弧,从而为进一步确定库地蛇绿岩的形成环境提供了新的佐证。

The basic igneous rocks, outcropped in Yexikegou, northwest of Kudi, is one of the most important components of the tectonically separated Kudi ophiolite in west Kunlun which is considered the northernmost border of the Gandwana plate as well as the oldest suture zone found in Tibet Plateau. So far, a lot of different opinions about its tectonic settings have been presented by different researchers, which gives rise to much confusion on the understanding upon its origin and evolutionary history. To clarify such confusion, a detailed field survey upon the geological section of the igneous rocks in Yexiekegou was conducted. In this paper, we use geochemical data from XRF, ICP-MS;and Sm/Nd isotope analysis as well as the published data in this area to make a synthetical determination upon its tectonic settings. Through different tectonic discriminant diagrams based upon major and trace element compositions of Yexiekegou basic igneous rocks together with their isotopic characteristics, accordant results can be obtained that they were formed in an oceanic island-arc tectonic environment. Therefore, it provides some new evidences for the constraint on the origin of Kudi ophiolite.