摘要
慕士塔格岩体是西昆仑造山带出露面积最大的侵入体,主要由黑云母二长花岗岩、似斑状黑云母二长花岗岩和花岗闪长岩组成,其中发育大量的暗色微细粒包体和基性岩浆条带。根据锆石的阴极发光图像以及Th、U、REE元素等特征,所测试的锆石均为典型的岩浆结晶锆石,利用LA-ICP-MS锆石U-Pb定年,测得岩体东西部分的加权平均206Pb/238U年龄分别为229.6±0.8Ma(MSWD=0.44)、232.8±1.5Ma(MSWD=0.21),两者在误差范围内一致,综合获得该岩体年龄为231.4±0.7Ma(MSWD=1.5),属于中三叠世晚期。根据岩石学、锆石内部结构及其REE元素特征,结合前人地球化学资料,该岩体应为壳幔岩浆混合成因。结合区域地质资料,慕士塔格岩体应是从挤压的主碰撞期向伸展后碰撞期转换的产物,表明古特提斯主碰撞作用发生在中三叠世晚期之前,之后开始进入古特提斯后碰撞阶段。
The Muztagata pluton is the largest granitic intrusion in Western Kunlun orogenic belt, which is composed of biotite monzonitie granite, porphyritic-like biotite monzonitic granite and granodiorite with a mass of widely developed dark microgranular enclaves and basaltic magmatie stripes. Noticed that the zircons of the rocks are typically magmatie zircon according to their cathodoluminescence （CL） image and characteristics of Th, U and REE. And the weighted mean age of ^206Pb/^238U to the western and eastern plutons are 229.6± 0.8Ma （MSWD = 0.44） and 232.8 ±1.5Ma （MSWD =0.21 ） respectively measured by LA-ICP-MS zircon U-Pb dating, which are consistent in error range. Accordingly, the Muztagata pluton is formed in 231.4 ± 0.7Ma （MSWD = 1.5）, representing an emplacement time of the Muztagata pluton in late Middle Triassic. Furthermore, the rocks are interpreted to have derived from magma mixing between crust and mantle by the proofs of petrology characteristics, internal structure and REE patterns of zircons, geochemistry data of predecessors. From the above and based on the regional geological data, Muztagata pluton was formed in the transitional period from primary collision to post- collision, indicating that the primary collision of Paleotethys in Western Kunlun occurred before late Middle Triassic, and entered post-collisional period from then on.
出处
《地质论评》
CAS
CSCD
北大核心
2012年第4期763-774,共12页
Geological Review
基金
中国地质调查局国土资源大调查研究项目(编号1212011085034)
陕西省自然科学基金资助项目(编号2012JM5004)的成果
