江西武功山地区老虎塘组碎屑锆石U-Pb年龄和Hf同位素:沉积时代厘定及其源区特征  

U-Pb and Hf Isotopic Data of Detrital Zircons from the Laohutang Formation in the Wugongshan Area, Central Jiangxi Province: Constraint on Sedimentary Age and Material Source

作　　者：王涛[1] 王宗起[2] 王东升[2] 吴富江[3] 王铭乾 马振慧[2] WANG Tao;WANG Zong-qi;WANG Dong-sheng;WU Fu-jiang;WANG Ming-qian;MA Zhen-hui(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037;Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037;Geological Survey of Jiangxi Province,Nanchang,Jiangxi 330201)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质科学院矿产资源研究所,北京100037 [3]江西省地质调查研究院,江西南昌330201

出　　处：《地球学报》2018年第2期167-178,共12页Acta Geoscientica Sinica

基　　金：国家自然科学基金项目(编号:41272220);国家重点研发计划(编号:2016YCF0600202);中国地质调查局地质调查项目(编号:DD20160201)联合资助~~

摘　　要：江西宜春武功山地区出露的震旦纪老虎塘组由薄层状的砂岩、粉砂岩和泥岩组成,岩石普遍经历了强烈的变形和变质作用。由于缺乏古生物化石和年龄值,其沉积时代和源区存在着争议。本文运用LA-ICP-MS技术,对老虎塘组两件变砂岩中的碎屑锆石进行了U-Pb和Hf同位素测定,共获得187个U-Pb年龄值,主要位于423~537 Ma和660~1 280 Ma两段。两个样品中最年轻的碎屑锆石年龄为(432.7±1.8)Ma,结合区域地质资料限定老虎塘组形成时代为志留纪。锆石U-Pb年龄和Hf同位素表明,年龄为423~537 Ma的碎屑锆石主要来源于华夏板块北缘加里东期的花岗岩,而年龄为660~1 280 Ma碎屑锆石显示物源主要来自钦—杭结合带,而其它少量的古元古代和太古代物质可能主要来源于华夏板块基底或者再循环的物质。因此,碎屑锆石年龄显示老虎塘组物源主要来源于华夏板块北緣加里东期岩浆岩和钦—杭结合带。大量的早古生代碎屑锆石数据反映了华夏板块北緣加里东期的造山事件,这次造山事件为早古生代晚期沉积盆地提供了大量的物质来源。The Sinian Laohutang Formation,outcropped in the Wugongshan area on the northern margin of the Cathaysia plate,is composed of thin bedded sandstone,siltstone and chert.The sedimentary rocks have undergone strong deformation and metamorphism.There is some controversy on the age of the sedimentary rock due to the lack of paleontological evidence.This study shows that the ages of detrital zircons from the sandstones are predominantly Early Paleozoic,and the youngest detrital zircon grains clearly show that the maximum depositional age of the Laohutang Formation is ca.(432.7±1.8)Ma.The ages of the detrital zircons can be dominantly divided into two groups:423~537 Ma and 660~1 280 Ma.The zircons in the 423~537 Ma age population show approximately the sameεHf(t)values from–20 to+5,suggesting that the source rocks were the igneous rocks formed on the northern margin of the Cathisian block in the Caledonian period.Zircon with ages from 660 Ma to 1 280 Ma shows the Hf values ranging from–20 to+5.The age data are comparable with the ages of zircons in the Neoproterozic granites and volcanic rocks in the Qinhang belt.The small Paleoproterozoic and Archean zircon population implies the probably derivation of the materials from the basement of the Cathaysia plate.A comprehensive analysis shows that there was a collision-orogenic event on the northern margin of the Cathaysia plate in the Caledonian period,and the orogenic belt contributed abundant materials to the sedimentary basin.

关 键 词：碎屑锆石 LA-ICP-MS U-PB年龄 沉积时代 老虎塘组 武功山 

分 类 号：P578.941[天文地球—矿物学] P597.1[天文地球—地质学]