川西地区中侏罗统沙溪庙组砂岩地球化学特征及构造意义

Tectonic Setting and Geochemical Characteristics of Sandstone from Middle Jurassic of Shaximiao Formation in Western Sichuan Area

沉积盆地中砂岩的地球化学成分主要受物源区控制,因此通过对砂岩化学成分的分析可以揭示盆地沉积物的源区构造背景及物源属性。为了深入探讨川西坳陷中侏罗统沙溪庙组的物源及其源区属性,对研究区的稀土元素、微量元素地球化学特征进行系统的分析。应用稀土元素La/Yb-∑REE、微量元素La/Th-Hf和La/Sc-Co/Th源岩属性判断图解以及微量元素构造背景判别图解,对研究区物源及其源区属性进行了深入的讨论。结果表明:根据研究区上、下沙溪庙组地球化学特征,认为上、下沙溪庙组具有相同的物源;通过对稀土元素及微量元素特征值及比值的分析,认为该地区属于构造背景主要为大陆岛弧向活动大陆边缘转换的构造背景;沉积物物源的原始物质应主要来自上地壳,部分来自混合长英质/基性源;结合研究区周缘山系的属性分析,认为研究区在中侏罗世沙溪庙期同时受到了米仓山-大巴山及龙门山的物源的影响。

The geochemical characteristics of clastic rocks are mainly controlled by its provenance. clastic rocks chemical composition analysis is the paramount clause to ascertain the basin evolution,and a significant basis for reconstruction the tectonic setting and palaeoenvironment of basin. To elucidate deeply the provenance and its properties of middle jurassic Shaximiao formation,western Sichuan area,the chipping component and its geochemical characteristics of rare earth elements and trace elements were analysed systematically,applied Dickinson triplot,and the diagrams reflecting provenance properties of La / Yb-∑ REE,La / Th-Hf,La / Sc-Co / Th. The geochemical characteristics of the lower and uppur Shaximiao formation showed that they have the same provenance. And based on Dickinson triplot and geochemical characteristics,the study area was suggested belonged to the tectonic background of transition stage from oceanic arc to continental margin. The Prime Material of provenance of the deposites maybe mainly come from the upper crust,and part from mixed source of felsic rock / basic rock. Combined the attribute analysis of peripheral mountains of the study area,we propose that the provence of Micang-Daba mountains and Longmen mountains influenced the study area simultaneously in Shaximiao period middle Jurrassic.