四川米易垭口地区前震旦纪五马箐组变沉积岩元素地球化学特征及其构造意义  

GEOCHEMICAL ELEMENT CHARACTERISTICS AND TECTONIC SIGNIFICANCE OF PRE-SINIAN WUMAQING FORMATION METASEDIMENTARY ROCKS IN YAKOU AREA,MIYI COUNTY,SICHUAN PROVINCE

作　　者：范伟 陈友良[1,2] 殷桂芹 朱桃秀 詹国鑫 郭俏萍 FAN Wei;CHEN Youliang;YIN Guiqin;ZHU Taoxiu;ZHAN Guoxin;GUO Qiaoping(College of Earth Science,Chengdu University of Technology,Chengdu,Sichuan 610059,China;Sichuan Key Laboratory of Geosciences and Nuclear Technology,Chengdu University of Technology,Chengdu,Sichuan 610059,China;Southeast Sichuan Geological Group,Chongqing Bureau of Geology and Minerals Erploration,Chongqing400038,China;Sichuan Geological Society,Chengdu,Sichuan 610081,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]成都理工大学地学与核技术四川省重点实验室,四川成都610059 [3]重庆市地质矿产勘查开发局川东南地质大队,重庆400038 [4]四川省地质学会,四川成都610081

出　　处：《矿物岩石》2023年第4期20-32,共13页Mineralogy and Petrology

基　　金：国家自然科学基金(项目批准号:42072096);中国核工业地质局重点科研项目“康滇地轴前寒武纪地质构造演化及其对铀成矿的制约”(编号:2023-16);成都理工大学珠峰科技计划(项目编号:2023ZF11413)。

摘　　要：近年来的研究表明,分布于四川米易垭口地区前震旦纪五马箐组变沉积岩的沉积时代属中元古代晚期,但对其沉积物的物质来源和沉积时的构造环境仍缺少深入的探讨。本次研究对米易垭口地区五马箐组变沉积岩的元素地球化学特征进行了系统分析,结果表明:米易垭口地区五马箐组变沉积岩在主量元素上显示富硅(w(SiO_(2))均值为73.28%)、富铝(w(Al_(2)O_(3))均值为13.23%)、贫钙(w(CaO)均值为0.50%)、贫镁(w(MgO)均值为0.85%)的特点,其原岩应为一套以杂砂岩、黏土岩等为主的泥砂质沉积岩。变沉积岩的化学蚀变指数(CIA)均值为71.6,成分变异指数(ICV)均值为0.93,指示变沉积岩物源区为温暖湿润的气候条件,经历了中等程度的风化作用,属近源沉积的产物。变沉积岩的Al_(2)O_(3)/TiO_(2)比值(均值为27.8)、Al_(2)O_(3)/(Al_(2)O_(3)+Fe_(2)O_(3))比值(均值为0.80)以及轻稀土富集、重稀土亏损(ΣLREE/ΣHREE均值为8.17)和具有明显的负Eu异常(δEu均值为0.52)等,反映垭口地区五马箐组变沉积岩的物源以中酸性岩石为主,并有一定程度的循环再沉积,沉积时的构造环境属被动大陆边缘,为探讨扬子板块西缘中元古代晚期的构造背景提供了新的依据。Recent studies show that the sedimentary age of Wumaqing Formation metasedimentary rocks in Yakou area of Miyi County,Sichuan Province belongs to the late Mesoproterozoic era.However,there is lack of the material source and tectonic environment of the Wumaqing Formation metasedimentary rocks.Therefore,the systematic analysis of geochemical elements of formation metasedimentary rocks in this area were systematically analyzed,and the results showed that the Wumaqing Formation metasedimentary rocks are rich in silicon(average w(SiO_(2))=73.28%)and aluminum(average w(Al_(2)O_(3))=13.23%),poor in calcium(average w(CaO)=0.50%)and magnesium(average w(MgO)=0.85%).The original rock is a set of argillaceous sedimentary rock mainly composed of greywacke and claystone.The mean value of the chemical alteration index(CIA=71.6)and the mean value of the compositional variation index(ICV=0.93)indicates that the depositional environment of source area of the metasedimentary rocks was warm and humid.The rocks experienced moderate weathering and belonged to proximal sedimentary products.Al_(2)O_(3)/TiO_(2) ratio(mean=27.8),Al_(2)O_(3)/(Al_(2)O_(3)+Fe_(2)O_(3))ratio(mean=0.80),ratio of enriched light rare earth enrichment and deplete heavy rare earth(mean ΣLREE/ΣHREE=8.17)and obvious negative Eu anomaly(mean δEu=0.52)of the Wumaqing Formation metasedimentary rocks indicate that the rock source is mainly derived from medium acid rock and cyclic redeposition to a certain extent and the tectonic environment during sedimentation of Wumaqing Formation was a passive continental margin.The research in this paper provides a new basis for exploring the late middle Proterozoic tectonic background of the western margin of Yangtze Plate.

关 键 词：垭口地区 五马箐组 变沉积岩 元素地球化学特征 构造环境 

分 类 号：P595[天文地球—地球化学]