西藏措勤盆地北缘麦堆构造混杂岩带及变质超基性岩

The Maidui tectonic mélange zone and metamorphic ultrabasic rocks on the northern margin of the Coqen Basin,Xizang

关键词:  措勤  麦堆  构造混杂岩带  西藏

Key words:  Coqen  Maidui  tectonic mélange zone  Xizang

摘要:

麦堆构造混杂岩带位于班公湖-怒江结合带南侧、措勤盆地的北缘,由性质不同的各种构造岩片组成,岩片呈近东西向展布,之间多为构造接触,多期变形明显。其中的变质超基性岩岩片宽数米—数十米不等,经历了强烈的蛇纹石化、硅化及碳酸盐化。变质超基性岩虽然化学成分变化很大,但仍具较高的MgO、Cr、Co、Ni含量和mf比值,属阿尔卑斯型超镁铁质岩,是残余地幔的组成部分。该带变质超基性岩及其伴生硅质岩应属蛇绿岩构造残片,是麦堆构造混杂岩的一部分,其形成与班公湖-怒江特提斯洋向南的俯冲有关,是早中侏罗世弧后或弧间小洋盆环境的产物。

Abstract:

The Maidui tectonic mélange zone located on the southern side of the Bangong-Nujiang suture zone and northern margin of the Coqen Basin, Xizang is a newly discovered melange zone within the Shiquanhe-Namco tectonic-ophiolitic mélange zone and consists of the slices of flysch,island-arc basic and intermediately basic volcanic rocks, exotic limestone,siliceous rocks,metamorphic ultrabasic rocks and diabase,which are oriented nearly EW and exhibit multiphase deformation.The metamorphic ultrabasic rocks have undergone the metasomatism and alteration from serpentinization through silicification to carbonatization,and plastic and brittle deformation,and are characterized by highly variable petrochemical compositions,higher MgO,Cr,Co and Ni contents and higher m/f ratios,and typical of the Alpine ultramafic rocks as part of residual mantle The Maidui tectonic mélange zone constitutes an important element of the Shiquanhe-Mangguoco-Namco-Lhari tectonic-ophiolitic mélange zone,and was formed in the Early and Middle Jurassic small back-arc and / or inter-arc oceanic basins associated with the southward subduction of the Bangong-Nujiang oceanic crust.