贵州官坝地区二叠系-三叠系地质界面黏土岩的火山岩特征、LA-ICP-MS锆石U-Pb年龄及其地质意义  

Volcanic Characteristics,LA-ICP-MS Zircon U-Pb Ages of Claystone at the Permian-Triassic Boundary,Guanba Area in Guizhou Province,South China and the Geological Implications

作　　者：何碧 张向文 赵飞 金灿海[2] 任光明[2] 王宁祖 张文斌 张志玺 孙平原 HE Bi;ZHANG Xiangwen;ZHAO Fei;JIN Canhai;REN Guangming;WANG Ningzu;ZHANG Wenbin;ZHANG Zhixi;SUN Pingyuan(The Second Institute of Geology and Minerals Exploration Team,Gansu Provincial Bureau of Geology and Minerals Exploration and Development,Lanzhou,Gansu730020,China;Chengdu Center,China Geological Survey,Chengdu,Sichuan610081,China)

机构地区：[1]甘肃省地质矿产勘查开发局第二地质矿产勘查院,甘肃兰州730020 [2]中国地质调查局成都地质调查中心,四川成都610081

出　　处：《现代地质》2020年第5期1028-1042,共15页Geoscience

基　　金：中国地质调查局地质调查项目“乌蒙山区地质矿产综合调查”项目(DD20160019);中国地质调查局成都地质调查中心项目“贵州乌蒙山区1∶5万店子场(G48E006018)、大关(G48E007017)、六厂(G48E007018)3幅区域地质调查”(DD20160019-04)。

摘　　要：贵州省黔西县官坝地区位于华南板块西南部,其二叠系—三叠系界线剖面出露较好,界线处出露3层黏土岩。采集贵州黔西官坝地区二叠系—三叠系地质界面黏土岩1件U-Pb年龄样品、7件地球化学样品,对其锆石进行U-Pb定年以及主量、微量和稀土元素进行测试分析。锆石LA-ICP-MS U-Pb分析结果表明,U和Th含量分别为60.26×10^-6~297.9×10^-6和46.14×10^-6~244.26×10^-6,Th/U比值介于0.76~1.55之间,为典型的岩浆锆石;获得206Pb/238U加权平均年龄为(252.6±1.4)Ma,谐和年龄为(252.7±0.6)Ma。地球化学分析结果显示,黏土岩属于高硅、铝、钾、镁,低铁、钛的钙碱质中酸性火山物质,具有稀土元素总量相对较高、相对富集轻稀土元素和轻、重稀土元素分馏程度高的特征,负Eu异常明显,δEu=0.19~0.45。上述岩石地球化学特征表明,贵州黔西官坝地区(华南板块西南)二叠系—三叠系界线位置总体上可与浙江长兴(华南板块东南)海相二叠系—三叠系界线(金钉子)相比较。Three Permian-Triassic claystone are outcropped at Guanba(Qianxi County)in Guizhou Province,geologically in the southwestern South China block.One sample for zircon U-Pb dating and 7 samples for geochemical analysis were collected from the base of the claystone.LA-ICP-MS zircon U-Pb analysis shows that the zircons have 60.26×10^-6-297.90×10^-6 U and 46.14×10^-6-244.26×10^-6 Th,with Th/U value of 0.76-1.55,resembling typical igneous zirconsZircon U-Pb dating yielded a 206Pb/238U weighted mean age of(252.6±1.4)Ma,and the concordant age of(252.7±0.6)Ma.Geochemical analysis shows that the tuff contains calc-alkaline volcanic materials with high Si-Al-K-Mg contents and low Fe-Ti contents.Additionally,the claystone has relatively high total REE contents,with elevated LREE enrichments and REE fractionation.Negative Eu anomaly is obvious(δEu=0.19-0.45).Geochemical characteristics indicate that the Permian-Triassic boundary at Guanba is comparable to the marine-facies Permian-Triassic boundary at Changhsing(GSSP,southeastern South China block).

关 键 词：二叠系—三叠系界线 黏土岩 LA-ICP-MS锆石U-PB年龄 官坝地区 

分 类 号：P534.51[天文地球—古生物学与地层学] P588.22[天文地球—地质学]