重庆城口地区早前寒武系黑色岩系研究:(3)巴山组硅质岩中PGE异常的地球化学研究

PRE-EARLY CAMBRIAN BLACK ROCK SERIES IN CHENGKOU DISTRICT,CHONGQING:(3) PGE GEOCHEMISTRY OF LOWER-CAMBIRAN CHERTS IN BASHAN GROUP.

以猪草河剖面和羊儿坝剖面为例,进行硅质岩的PGE与微量元素等地球化学分析,结果表明:槽区硅质岩中的PGE异常受控于硅质岩中火山物质(蚀变成粘土矿物)的多少,PGE与Sc、Rb、Cs、Ti、Cr、Zr等具有良好的相关性;猪草河剖面远离陆源区,沉积厚度大,更靠近火山活动区域,接受火山粗碎屑物质的量多;羊儿坝剖面远离火山活动中心,主要接受了火山灰等细碎屑物质,更接近陆源区,受一定量的陆源碎屑物质影响。根据Cr/Co、Nb/Ta、Pd/Ir-Ni/Cu及Ni/Pd-Cu/Ir对岩浆性质的约束,当时岩浆性质为基性玄武岩。根据La-Y-Nb图解和Th-Hf-Ta图解的进一步约束,表明当时的火山岩浆性质为钙碱性的火山弧玄武岩。

According to the geochemical analysis of the PGE and trace dements in the siliceous rocks from the Zhucaohe and Yang＇ erba sections, it is concluded that ： （1） the PGE anomaly relies on the quantity of magmagene ingredients （clay minerals, etc. ） in geosynclinal siliceous rocks, and the PGE are closely related with some elements such as Sc, Rb, Cs, Ti, Cr, Zr, etc; （2） the Zhucaohe section with thicker sediments and much bigger volcanic debris is far from the landderived region and close to the volcanically active area; while the Yang＇ erba section with much smaller volcanic ashes is far from the center of volcano activity area and close to the land-derived region and affected by certain land-derived debris; （3） the constraints of Cr/Co, Nb/Ta, Pd/Ir-Ni/Cu and Ni/Pd-Cu/Ir on magma quality indicate that the temporal magma is characteristic of basic basalts; and （4） the further constraints of La-Y-Nb and Th-Hf-Ta indicate that the temporal magma is characteristic of calc-alkaline island-arc volcanic basalts.