湖北宜昌地区第四纪沉积物中锆石的U-Pb年龄特征及其物源意义  

LA-ICP-MS U-Pb GEOCHRONOLOGY OF ZIRCONS IN THE QUATERNARY SEDIMENTS FROM THE YICHANG AREA OF HUBEI PROVINCE AND ITS PROVENANCE SIGNIFICANCE

作　　者：向芳[1] 杨栋[1] 田馨[1] 李志宏 罗来[1] 

机构地区：[1]成都理工大学沉积地质研究院,四川成都610059 [2]西安国林资源环境信息工程有限公司,陕西西安710075

出　　处：《矿物岩石》2011年第2期106-114,共9页Mineralogy and Petrology

基　　金：国家自然科学基金(41072083;40602011)

摘　　要：对于长江三峡的贯通近年来基本认为是第四纪以来的事件,但在具体贯通时间的认识上仍存在差异。紧邻三峡出口、具有第四纪以来完整地层和较好出露层位的江汉盆地西缘宜昌地区的第四纪沉积物沉积特征及测年资料显示,该地区的云池组为冲积扇—扇三角洲相沉积,善溪窑组下部为扇三角洲沉积,上部为湖相沉积。对云池组、善溪窑组、长江5级和4级阶地的015,024,YC02,00B剖面等4个典型剖面砾石层中砂质填隙物的锆石进行矿物学研究和LA-ICP-MS U-Pb年龄测定,发现015,024剖面中锆石主要来源于三峡以东的黄陵穹窿、武当地块,少量来自鄂陕边境的庙川地区和湘鄂交接的华容地区,均为三峡以东的物质来源。而长江第5,4级阶地沉积物中的锆石不仅存在上述三峡以东物源区的物质,同时出现三峡以西米仓山—大巴山地区、龙门山—攀枝花地区,以及川西巴塘—德格地区岩浆岩物源的物质,也具有来自峨眉山玄武岩的特征岩浆锆石的存在,从而证实了以015,024剖面为代表的沉积并非前人认为的长江阶地产物,同时也表明三峡的贯通应在024剖面沉积结束以后,YC02剖面沉积以前,即长江三峡贯通的时间应该在0.75 Ma以后。The cutting through of the Three Gorges of Yangtze River recently was considered as an event occurred in Quaternary Period,but there still has some diversity in the concrete time of cutting through.Therefore,the Jianghan Basin which is close to the outlet of the Three Gorges is selected as the research target and the entire Quaternary strata and preferable outcrop are thoroughly studied for this purpose.Detailed research of the sedimentary characters of Quaternary deposits,combing with the ESR dating data,following conclusions can be drawn.Yunchi Group belongs to sediments of alluvial fan and fan delta and the lower part of Shanxiyao Group is the product of sedimentation deposited in fan delta with the upper part being the lacustrine sediments.We select the profiles of 015,024,YC02,00B,which respectively represent Yunchi Group,Shanxiyao Group,the fifth level terrace and fourth level terrace of Yangtze River,and study their mineralogy characteristics and use LA-ICP-MS to date their U-Pb ages from detrital zircons of sandy matrix in gravel layer of this four sections.According to these researches,it is found that the zircons in the profiles of 015 and 024 mainly were derived from Huanglin Dome,Wudang Block,which lie in the east of the Three Gorges,and some derived form Miaochuan area which is in the border between the Hubei Province and Shanxi Province,and the rest derived from Huarong area which is in the border between the Hunan Province and the Hubei Province.These zircons are all the east of the Three Gorges.But the zircons in sediments of the fifth and sixth level terraces of Yangtze River contain not only the material deriving from the east area of the Three Gorges mentioned above,but also materials from exposed magmatic rocks in the west of the Three Gorges,such as the Micang Mountain,Daba Mountain area,Longmen Mountain,Panzhihua area and Batang-Dege area in the west of Sichuan,as well as from the Emeishan Basalt.Thereby,it is confirmed that the sediments represented by profiles of 015,024 are not the produc

关 键 词：宜昌地区 锆石LA-ICP-MSU-Pb测年 物源分析 长江三峡贯通时间 

分 类 号：P597.3[天文地球—地球化学]