东昆仑西段箭峡山岩体锆石U-Pb年代学、地球化学特征

Zircon U-Pb dating and petrogeochemistry of the Jianxiashan pluton in the western segment of east Kunlun

东昆仑西段阿克苏河一带箭峡山岩体主要由二长花岗岩与花岗闪长岩组成。为确定其形成时代、地质背景,对岩体中细粒黑云母二长花岗岩开展了同位素年代学与岩石地球化学研究,获得锆石LA-ICP-MS U-Pb年龄为(354.8±2.6)Ma(MSWD=0.80),表明其形成于早石炭世。岩石富硅(74.64%~77.38%)、富碱(6.75%~8.13%),属过铝质花岗岩;岩石具有Rb、U、Th相对富集,K、Ti、Nb、Ta相对亏损,轻、重稀土分馏较明显的特征,LREE/HREE值介于2.99~6.74之间,表现出较强的铕负异常(δEu=0.63~0.95);Al_(2)O_(3)值为12.15%~12.98%,铝饱和指数A/CNK值为1.18~1.20,具S型花岗岩特征。岩石成因与源区分析研究表明,岩浆来源于下地壳砂质岩石的部分熔融,结合东昆仑区域地质背景分析,箭峡山岩体形成于大陆边缘弧环境,为古特提斯洋壳俯冲作用背景下的大陆边缘弧岩浆活动产物。

The Jianxiashan pluton in the Aksu river area in the western section of the east Kunlun is mainly composed of monzonite and granodiorite.In order to determine its formation age and geological background,the isotopic dating of the fine-grained biotite monzonite in the pluton.The LA-ICP-MS U-Pb age of the zircon is(354.8±2.6)Ma(MSWD=0.80),indicating that it was formed in the early Carboniferous.The rocks are rich in silicon(74.64%~77.38%),rich in alkali(6.75%~8.13%),and belong to peraluminous granite.The rocks are relatively enriched in Rb,U,while Th,K,Ti,Nb,and Ta are relatively depleted,and fractionation between the light and heavy rare earth is obvious.The LREE/HREE value is between 2.99 and 6.74,showing a strong europium negative anomalies of Eu(δEu=0.63~0.95),Al_(2)O_(3) value is between 12.15%and 12.98%,and aluminum saturation index A/CNK values range from 1.18 to 1.20,with the characteristics of S-type granite.The study of petrogenesis and source area indicates that magma originated from partial melting of sandy rocks in the lower crust.Combined with the analysis of the geological background of the east Kunlun region,the Jianxiashan pluton was formed in the continental marginal arc environment,and was the product of continental marginal arc magmatism under the background of the Paleo-Tethys oceanic crust subduction.