扬子地块西缘河口群的时代:来自火山岩锆石LA-ICP-MS U-Pb年龄的证据  

GEOCHRONOLOGY OF THE HEKOU GROUP ON THE WESTERN MARGIN OF THE YANGTZE BLOCK:EVIDENCE FROM ZIRCON LA-ICP-MS U-PB DATING OF VOLCANIC ROCKS

作　　者：王冬兵[1] 孙志明[1] 尹福光[1] 王立全[1] 王保弟[1] 张万平[1] 

机构地区：[1]成都地质矿产研究所,四川成都610081

出　　处：《地层学杂志》2012年第3期630-635,共6页Journal of Stratigraphy

基　　金：国家重点研究发展计划项目(2009CB421003);中国地质调查局地质矿产调查评价专项项目(1212011085119;1212011085147;1212011121259)联合资助

摘　　要：扬子地块西缘的河口群长期以来被认为是早元古代的火山—沉积地层,这种认识缺乏高精度同位素年龄的支持。为精确标定河口群的时代,采用激光剥蚀等离子体质谱(LA-ICP-MS)对川西南拉拉铜矿区河口群中的石英角斑岩进行锆石U-Pb定年。结果表明所有锆石均为岩浆锆石,单点分析结果均为谐和年龄,锆石207Pb/206Pb加权平均年龄为1722±25Ma(2σ,MSWD=0.5,n=11)。由此认为河口群浅变质火山—沉积岩系的精确沉积时代为1722±25Ma,为早元古代晚期的火山—沉积地层。The Hekou Group on the western margin of the Yangtze Block has long been considered to be Paleoproterozoic volcanic-sedimentary strata. However, high-quality isotopic age in support of this inference is lacking. To determine the age of the Hekou Group, we carried out in-situ zircon LA-ICP-MS U-Pb dating of volcanic rocks of the Hekou Group in the Lala Copper Deposit area, southwestern Sichuan. The results show that all the analyses are concordant, and yield a weighted mean ^207Pb/^206Pb age of 1722±25 Ma （2a, MSWD=0.5, n=11）. We conclude that the Hekou Group is late Paleoproterozoic volcanic-sedi- mentary strata with a precise depositional age of 1722±25 Ma.

关 键 词：年代地层学 锆石U—Pb年龄 LA—ICP—MS 河口群 早元古代 扬子地块 

分 类 号：P533[天文地球—古生物学与地层学] P534.3[天文地球—地质学]