华夏陆块早寒武世沉积地层年代学与地球化学组成:对源区和构造背景的指示  

Geochronology and geochemical composition of the Early Cambrian sedimentary strata in the Cathaysia block: Implications for its provenance and tectonic setting

作　　者：陈伟雄 徐琼[1,2] 童喜润 顾涛[2] 散飞雪[3] 邱啸飞[1,2] CHEN Weixiong;XU Qiong;TONG Xirun;GU Tao;SAN Feixue;QIU Xiaofei(Institute of Geological Survey,China University of Geosciences,Wuhan,Hubei 430074,China;Wuhan Center of China Geological Survey,Wuhan,Hubei 430205,China;School of Earth Sciences,China University of Geosciences,Wuhan,Hubei 430074,China)

机构地区：[1]中国地质大学(武汉)地质调查研究院,湖北武汉430074 [2]中国地质调查局武汉地质调查中心,湖北武汉430205 [3]中国地质大学(武汉)地球科学学院,湖北武汉430074

出　　处：《地质学报》2023年第7期2157-2175,共19页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号42272229);自然资源部生态地球化学重点实验室开放基金项目(编号ZSDHJJ202005);国家重点研发计划项目(编号2020YFC1512400)联合资助的成果。

摘　　要：华夏陆块早古生代沉积记录对于了解华南陆块在Gondwana超大陆演化过程中所起的作用具有重要意义。本文对广东省中山市神湾地区下寒武统八村群开展了锆石年代学和元素地球化学研究。结果表明,八村群变泥质粉砂岩的碎屑锆石年龄可分为4034~3122 Ma、2765~2250 Ma、1765~1443 Ma、1126~901 Ma、884~773 Ma以及595~547 Ma六组,其中最年轻的一组碎屑锆石加权平均年龄将该地层的最大沉积时间限定在551±4 Ma。锆石的Hf同位素特征则指示八村群沉积物源可能以古老地壳物质再循环为主,伴少量初生地壳物质。八村群变粉砂岩和变泥岩样品的化学风化指数(CIA)和成分成熟度(ICV)分别为79.8~86.4和0.39~0.87,均表明源区经历了相对强烈的化学风化作用。元素地球化学结果显示,八村群样品强烈富集不相容元素,而亏损Ni、Cr和Co等,指示八村群源区可能以活动大陆边缘构造背景下的长英质岩石为主。综合对比八村群与世界其他陆块同时期沉积地层的碎屑锆石年龄组成,本文认为八村群代表了新元古代晚期至早古生代早期Gondwana超大陆聚合过程中造山作用的沉积响应,支持华夏陆块位于Gondwana超大陆北缘,靠近北印度板块和羌塘地体,是该超大陆的重要组成部分。The Early Paleozoic sedimentary records of the Cathaysia block are of great significance for understanding the role of the South China block in the evolution of the Gondwana supercontinent.In this study,zircon geochronological and elemental geochemical investigations are carried out for the Lower Cambrian Bacun Group in the Shenwan area,Zhongshan City of the Guangdong Province.The results show that detrital zircon ages of metaargillaceous siltstone in the Bacun Group can be divided into six groups:4034~3122 Ma,2765~2250 Ma,1765~1443 Ma,1126~901 Ma,884~773 Ma,and 595~547 Ma,with the weighted average age of the youngest group of detrital zircon constrains the maximum sedimentary age of the Bacun Group to 551±4 Ma.The Hf isotopic features of zircon constraining that the provenance of the Bacun Group might be dominated by recycling of ancient crustal materials,associated with small amount of juvenile crustal rocks.The chemical index of alteration(CIA)and the index of compositional variability(ICV)of metasiltstone and metamudstone from the Bacun Group are 79.8~86.4 and 0.39~0.87,respectively,suggesting that the provenance has experienced extensive chemical weathering.The Bacun Group samples show strong enrichment in incompatible elements but depletion in Ni,Cr,and Co,indicating that the provenance of the Bacun Group may be dominated by felsic rocks under active continental margin tectonic setting.Comparing the age composition of detrital zircon in the Bacun Group with the other contemporaneous continental blocks in the world,it is suggested that the Bacun Group may represent the sedimentary response of the orogeny during the assembly of the Gondwana supercontinent from Late Neoproterozoic to Early Paleozoic,supporting the view that the Cathaysia block is located in the northern margin of Gondwana supercontinent,close to the Northern Indian block and the Qiangtang terrane.

关 键 词：华夏陆块 八村群 Gondwana超大陆 构造背景 源区 

分 类 号：P534.41[天文地球—古生物学与地层学] P597.3[天文地球—地质学] P535