东昆仑南缘布青山构造混杂岩带的地质特征及大地构造意义

在1∶50000地质填图的基础上,运用详细的野外剖面测制、岩石组合分析、LA-ICP-MS锆石U-Pb同位素定年等研究手段,将东昆仑南缘布青山构造混杂岩划分为基质和构造混杂岩块。构造混杂岩块包括变质基底岩块、洋壳型岩块和岛弧型岩块。其中,洋壳型混杂岩块又细分为早古生代蛇绿岩(516.4Ma±6.3Ma)、晚古生代蛇绿岩(332.8Ma±3.1Ma)和海山/洋岛玄武岩;岛弧型混杂岩块细分为加里东期中酸性侵入岩岩块(441.1Ma±6.3Ma)和火山熔岩岩块。建立了东昆仑南缘布青山构造混杂岩带2套典型的古洋盆扩张、俯冲消减的物质组合,分别代表东原特提斯洋和东古特提斯洋的形成与演化,从而为研究东特提斯洋演化的进程提供了新证据。

Geological characteristics of the Buqingshan tectonic melange belt in the southern margin of East Kunlun and its tectonic implications

On the basis of geological mapping on the scale of 1∶50000 in the Buqingshan area on the southern margin of the East Kunlun Mountains and by means of detailed field section measurement and rock assemblage analysis as well as LA-ICP-MS zircon U-Pb dating, the authors have divided the melange into two parts, i.e., matrix and tectonic melange rock blocks. The includes metamorphic basement rock block, oceanic crust type rock block and island-arc type rock block, in which the ocean-crust type rock block can be further divided into Early Paleozoic ophiolite(516.4±6.3Ma), Late Paleozoic ophiolite(332.8±3.1Ma)and seamount or island basalt, whereas the island-arc type rock block is composed of Caledonian island-arc type granodiorite(441.1±6.3Ma)and middle-acid volcanic rocks. It is thus concluded that there are two typical rock assemblages of paleo-ocean basin's spread and subduction in Buqingshan ophiolite complex belt, which represent the formation and evolution of eastern Proto-Tethys and eastern Paleo-Tethys respectively. The results provide new evidence for the study of evolution process of East Tethys.