藏北羌塘南部冈玛错地区展金组玄武岩的成因及其构造意义

羌塘南部地区大面积出露玄武岩、基性岩墙等基性岩类,区域上它们沿龙木错—双湖—澜沧江板块缝合带南侧展布。已有较多的研究报道认为基性岩墙的时代为晚石炭世—早二叠世。玄武岩呈夹层状产出于展金组中,随着羌塘地区地质研究程度的不断提高,玄武岩的确切时代、构造属性等已成为探讨研究区构造演化亟待解决的问题。在野外观察的基础上,选择羌塘南部典型的玄武岩进行地球化学研究。玄武岩属于碱性系列岩石,富集Ti和Fe;轻稀土元素富集,轻、重稀土分异明显;在构造环境判别图解上,主要投在板内环境区域;总体表现出与地幔柱成因同类岩石相似的特点。对玄武岩的研究,为羌塘南部晚古生代地幔柱的存在提供了有力的证据。

Petrogenesis of the basalt of Zhanjin Formation in the Gangmar Co area, southern Qiangtang, and its tectonic implications

There are widespread basic dykes and basalt distributed on the southern side of the Lungmu Co-Shuanghu-Lancang River suture zone trending nearly EW in southern Qiangtang. Basalts occur as interlayers in the Zhanjin Formation. Whole-rock compositions show that the southern Qiangtang basalts are alkaline and rich in Fe + Ti, and exhibit relative enrichment of light rare earth elements (LREE). Based on geochemical diagrams, the authors infer that the southern Qiangtang basalts erupted in an intraplate environment. It is concluded that the basalts in southern Qiangtang were related to the Permian mantle plume activity. The results achieved by the authors provide convincing evidence for the existence of the late Paleozoic mantle plume in southern Qiangtang.