新疆大黑山东部姜巴斯套组下段的凝灰岩锆石LA—ICP—MSU—Pb年龄及其地质意义  

Crystal Tuff Zircon LA-ICP-MS U-Pb Ages from the Lower Jiangbasitao Formation in the East Daheishan Area,Xinjiang and Their Geological Implications

作　　者：樊婷婷[1] 周小虎[1] 柳益群[1] 李玮[1] 郑朝阳[1] 胡亭[2] 梁浩[2] 

机构地区：[1]大陆动力学国家重点实验室西北大学地质学系,西安710069 [2]中国石油天然气总公司吐哈油田分公司勘探开发研究院,新疆哈密830002

出　　处：《沉积学报》2011年第2期312-320,共9页Acta Sedimentologica Sinica

基　　金：大陆动力学国家重点实验室自主研究课题(编号:BJ091358);中国石油化工股份有限公司重大项目(编号:YPH08103)联合资助

摘　　要：准噶尔东部大黑山地区出露的姜巴斯套组为一套厚层海相火山—沉积地层,其形成时代及地层层序存在争议。对姜巴斯套组下段2个具有地层意义的晶屑凝灰岩开展的锆石LA—ICP—MS测年,获得的加权平均年龄分别为339.4±1.9 Ma(MSWD=0.39)和336.3±2.6 Ma(MSWD=0.58),结合古生物新的研究成果,确定了该套地层时代为早石炭世。其中,最老的继承性单颗粒碎屑锆石谐和年龄为2999±51 Ma,推测该区应存在前寒武纪古老地块,因此准噶尔盆地东北缘古生代山系由两条蛇绿岩、蛇绿混杂岩带围限的区带,应是由蛇绿岩、蛇绿混杂岩地体、岛弧岩浆杂岩和微古陆块共同组成的古生代增生带。The Daheishan area is located in the south of the Santanghu Basin,north to the Balikun-Kaerlikeshan, and is adjacent to the Tu-ha Basin,which is located in the Paleozoic Orogenic Belt of eastern edge of Junggar basin. A suite of thick-bedded marine volcanic-sedimentary rocks——consist mainly of tuffaceous sandstones and siltstones, tuffs,muddy siltstones,silty mudstones,mudstones,and conglomerates are distributed in the Daheishan region in east Junggar,of which the ages and stratigraphy are highly controversial.More importantly,as the study area is sandwiched between the Zhaheba-Aermantai and the Kelamaili-Takezhale ophiolitic melange belts,it is of importance to investigate the stratigraphy.Two crystal tuff horizons（Nos.DHS04N and DHS07N）are sampled from the Jiangbasitao Formation of Lower Carboniferous and are dated using zircon LA-ICP-MS method.The analysis shows that the zircons are of typical magmatic origin with oscillatory zoning.Samples of DHS04N have a uranium content of 63～642 μg/g,thorium of 19～1037μg/g,and a Th/U value range between 0.29 and 1.89.Whereas those of DHS07N have a uranium content of 40～476μg/g,thorium of 25～466μg/g,and Th/U of 0.48～1.14.The dating results yield two weighted mean2 06Pb/ 238 U ages of（339.4±1.9）Ma（MSWD=0.39）and（336.3±2.6）Ma（MSWD= 0.58）,respectively.These two radiometric ages are well consistent and are interpreted to represent the crystallization age of the zircons from the tuff and also the age of the sedimentation of the tuff sequence,indicating that the tuff sequence should be ascribed to the Visean Stage（ca.345～328 Ma）of the Early Carboniferous.Newly found fossil evidence—e.g.,brachiopoda index fossils Stratifera magna,Gigantoproductus striato-sulcatus,and Gigantoproductus edelburgensis—also indicates the Early Carboniferous age of the sequence.Combining the new paleobiological data, we assign these successions to the Early Carboniferous in age.Two zircon samples show concordia ages of 352～ 2 999 Ma and CL images of the

关 键 词：晶屑凝灰岩 姜巴斯套组 锆石 LA - ICP - MS 测年 准噶尔盆地 

分 类 号：P597.3[天文地球—地球化学]