东昆仑埃坑德勒斯特二长花岗岩锆石U-Pb定年及地质意义

Zircon U-Pb Ages and Its Geological Significance of the Monzonitic Granite in the Aikengdelesite, Eastern Kunlun

埃坑德勒斯特是近年来在东昆仑地区发现的首例典型的斑岩型钼(铜)矿,其矿床与区域地质研究程度很低。矿床产于东昆南复合拼接带,容矿围岩为闪长岩、二长花岗岩、花岗斑岩、中细粒花岗岩及洪水川组火山-沉积岩。笔者重点对主要容矿围岩二长花岗岩进行了LA-ICP-MS锆石U-Pb测年。花岗岩中锆石呈自形-半自形,发育典型的岩浆锆石振荡生长环带,Th/U值较高(0.83～1.47,平均为1.15),为典型的岩浆锆石。测得二长花岗岩U-Pb加权平均年龄为(268.7±1.6)Ma,MSWD=0.24;谐和年龄值为(268.5±0.83)Ma,MSWD=0.051,属晚华力西期,较前人认为的晚印支期早。综合分析认为,268Ma±区内已经进入大洋俯冲阶段。

Aikengdelesite is the first found porphyry molybdenum （copper） deposit in Eastern Kunlun for the past years and the degree of geological work and research for the deposit is quite low. The deposit lies to the Eastern Kunlun southern composite accretion belt. The hosted rocks are diorite , monzonitic granite, granite porphyry , medium-fine grain granite and volcanic rocks and sedimentary rocks of Hongshuichuan Group . In this paper, we present zircon U-Pb age data of monzonitic granite using laser ablation ICP-MS technique. The zircons of granite are mainly euhedral and hypidiomorphie texture, have clear ring and high Th/U ratio （0. 83;1.47, average 1.15） which belong to the typical magmatic zircons. The results show that the intrusion mainly comes from late Hercynian but not late Indosinian period with the 206Pb/238 U average weighted age of （268.7±1.6） Ma （MSWD=0.24） and concordant age of （268.5±0. 83） Ma （MSWD= 0. 051） . Comprehensive analysis reveals that the research area has entered into oceanic crust subduction stage in 268 Ma±.