西准噶尔地区洋陆转换时代:来自锆石U-Pb定年与Lu-Hf同位素的约束  

Time of the ocean-continent transition in West Junggar: Constraints from zircon U-Pb dating and Lu-Hf isotopic composition

作　　者：徐盛林[1,2] 陈宣华 李廷栋[1,2] 丁伟翠[1,2] 史建杰 李冰[1] 马飞宙 XU Shenglin;CHEN Xuanhua;LI Tingdong;DINGWeicui;SHI Jianjie;LI Bing;MAFeizhou(Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China;China Geological Survey,Beijing 100037,China)

机构地区：[1]中国地质科学院,北京100037 [2]中国地质大学(北京)地球科学与资源学院,北京100083 [3]中国地质调查局,北京100037

出　　处：《中国地质》2019年第5期1061-1078,共18页Geology in China

基　　金：中国地质调查局地质调查项目（DD20160083、DD20190011、DD20160344-05）;中央级公益性科研院所基本科研业务费项目（CAGS-YWF201706）;国家重点研发计划项目（2018YFC0603700）联合资助~~

摘　　要：中亚造山带西部的西准噶尔地区是古生代洋陆构造转换最显著的地区之一,但是关于该地区洋陆转换的具体时间和地壳演化至今仍存在诸多争议。本文以西准噶尔地区的庙尔沟岩体及其西北侧新发现的柱状节理流纹岩为研究对象,通过锆石U-Pb定年的方法,判断庙尔沟岩体的年龄为302.8~308.8 Ma,柱状节理流纹岩的年龄为303.6~294.5 Ma。锆石Lu-Hf同位素测试结果显示,庙尔沟岩体和柱状节理流纹岩都具有相似的高176Hf/177Hf值和高正εHf(t)值,具有亏损地幔的源区属性,可能来源于下地壳底部残余洋壳或火山岛弧等新生地壳发生部分熔融。结合区域地质资料和前人研究成果,将西准噶尔地区由大洋俯冲向陆内环境转变的时间限定为晚石炭—早二叠世,其基底可能是以新元古代晚期—晚古生代形成的年轻洋壳和岛弧为主,不存在古老的结晶基底。The West Junggar area of the western Central Asian Orogenic Belt is one of the most typical regions related to transition from the ocean to the continent in the late Paleozoic.It is still controversial about the specific time of ocean-continent transition and the continental growth of the West Junggar area at present.This paper reports zircon U-Pb age and zircon Lu-Hf isotope analytical results from the Miaoergou batholith and the newly discovered columnar jointed rhyolites on the northwest side of the Miaoergou batholith,West Junggar area.The zircon U-Pb ages indicate that the Miaoergou granitoids were formed at 302.8~308.8 Ma and the columnar jointed rhyolites were formed at 303.6~294.5 Ma,which indicates that the specific time of ocean-mainland transformation of the West Junggar area is limited to the Late Carboniferous-Early Permian.The zircon Lu-Hf isotope analytical results show that the Miaoergou granitoids and rhyolites have some similar characteristics in 176Hf/177Hf ratios andεHf(t)values.High 176Hf/177Hf ratios andεHf(t)values,similar to features of depleted mantle in nature,suggest that they resulted from partial melting of juvenile crust.Integrating regional geological data and previous research,the authors have reached the conclusion that the basement of West Junggar area was composed of juvenile oceanic crust and island arc which grew from late Neoproterozoic to late Paleozoic,with no old crystalline basement.

关 键 词：西准噶尔 洋陆转换 庙尔沟岩体 柱状节理流纹岩 锆石U-PB定年 锆石Lu-Hf同位素 深地勘查工程 

分 类 号：P597[天文地球—地球化学] P542[天文地球—地质学]