湘西花垣排碧寒武系混积岩的沉积地球化学特征及陆源碎屑的物源属性

Sedimentary Geochemical Characteristics of the Diamictite of Series 3 of Cambrian System in the Paibi Profile,Huayuan County,Hunan Province,China and the Provenance Attribute of Terrigenous Clastics of the Diamictite

花垣排碧剖面位于扬子板块东南边缘,发育特殊的寒武系第三统陆源碎屑-碳酸盐混积岩。文章以沉积地球化学分析为主要手段,并结合混积岩种类、成因及沉积环境分析,探讨了碎屑物源属性及其构造意义。分析结果显示,混积岩碳酸盐组分和陆源碎屑组分混合沉积,相对比值从1∶1-1∶9.8;含有较高的Si O2与Ca O,La、Th、Zr及Sc等元素及其之间的比值主要受控于陆源碎屑且相对稳定。元素特征指示第三统混积岩的碎屑物质主要来自于大陆岛弧源区,具体为长英质-铁镁质混合源区以及靠近安山质岛弧源区。结合区域构造背景,认为排碧剖面寒武系第三统混积岩的陆源碎屑来自新元古代扬子与华夏俯冲碰撞中形成的大陆岛弧。据此推测,寒武纪第三世,扬子碳酸盐岩台地的东南缘已受到＂华夏地块＂及华夏-扬子古老结合带的影响,其间并无＂华南残留洋盆＂相隔。

The Paibi profile in Huayuan County is tectonically located in the southeastern margin of the Yangtze plate. A special set of terrigenous clastic-carbonate diamictite is developed in Series 3 of Cambrian system in the Paibi Profile. In this paper,the sedimentary geochemical analysis is mainly used to analyze type,diagenesis and sedimentary environment of the clastic-carbonate diamictite,and to discuss the provenance attribute of clastics of the diamictite and its tectonic significance. The results show that carbonate and terrigenous clastic components of the diamictite are mixed,with their ratios varying from 1 ∶1 to 1 ∶9. 8. The diamictite has relative high Si O2 and Ca O contents. Its La,Th,Zr,and Sc contents and ratios between each other of these elements are relatively stable,as they are mainly controlled by terrigenous detritus of the diamictite. The elemental characteristics of the diamictite show that its detrital materials were mainly sourced from the continental arc,possibly from mixture of felsic-mafic rocks and from the andesitic arc. Based on the regional tectonic setting,it is considered that the terrigenous clastics of the diamictite of Series 3 of Cambrian system in the Paiibi Profile were derived from the continental arc formed by the subduction of the Cathaysian Block to the Yangtze Block in Neoproterozoicera. Therefore,it is presumed that southeastern margin of the Yangtze Block has been influenced by the Cathaysia Block and the ancient suture belt between the Yangtze and Cathaysia blocks in Epoch 3 of Cambrian Period,with no ＂Southern China remnant basin＂existed between the Yangtze and Cathaysia blocks at that time.