三峡地区二叠系牙形石的U-Th-Pb定年及古海水信息  

U-Th-Pb dating and paleoseawater information of the Permian conodont of Three Gorges area

作　　者：王瑾[1] 周炼[1] 胡兆初[1] 赵来时[1] 张海强[1] 陈孝红[2] 李志红[2] 

机构地区：[1]中国地质大学(武汉)地质过程与矿产资源国家重点实验室,湖北武汉430074 [2]中国地质调查局地层古生物研究中心,湖北宜昌443003

出　　处：《古地理学报》2010年第2期212-219,共8页Journal of Palaeogeography：Chinese Edition

基　　金：国家自然科学基金项目(编号:40673020;40839903;40972003);教育部创新团队项目(编号:IRT0441);教育部"111"创新引智计划(编号:B07039);地质过程与矿产资源国家重点实验室开放基金资助

摘　　要：利用激光剥蚀电感耦合等离子质谱(LA-ICP-MS)对三峡地区二叠系茅口组牙形石的U-Th-Pb同位素年龄进行测定。结果表明该地层中牙形石的208Pb/232Th放射年龄为269±44,Ma,207Pb/235U放射年龄为256±39,Ma,接近二叠系茅口组的生物地层年龄。206Pb/238U的年龄为196±6,Ma,虽然准确度较高,但与前人推测的地层年龄相比偏低。此外,作者对牙形石的稀土元素(REE)组成进行了分析,并且发现牙形石的REE组成和Ce异常与古海水氧化还原条件有一定的相关性,可以指示古海水的信息。Laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） was used to establish radiometric U-Th-Pb ages and produce the records of rare earth elements （REE） of conodont of the Permian Maokou Formation in the Three Gorges area. Fourteen spots on the sample indicate a radio- metric ^208spb/^232Th age of 269±44 Ma and a radiometric ^207pb/^235U age of 256±39 Ma, which are consistent with the biostratigraphic ages of the Permian Maokou Formation. The age of ^206pb/^235U is 196±6 Ma, which is relatively lower compared with the stratigraphic ages predicted by preresearchers. The paleochemical characteristics of paleoseawater from the Permian conodont were reconstructed through contrastive researches of REE and Ce anomalies. The resuts show that geochemical characteristics of the conodont may be regarded as a useful proxy to reconstruct the paleoenvironment.

关 键 词：三峡地区 二叠系 牙形石 LA—ICP—MS U-Th—Pb定年 古海水 

分 类 号：P597[天文地球—地球化学]