香山群沉积岩浆记录及其反映的大地构造环境

Record of deposition-magmatism of Xiangshan Group and the reflection of tectonic environment

目的探讨鄂尔多斯西南边缘香山群形成的大地构造环境,为鄂尔多斯盆地西南缘早古生代大地构造背景的恢复和确定提供佐证。方法通过香山群地层的岩石学、沉积学、砂岩和火山岩的岩石地球化学特征的系统研究,综合分析香山群形成的大地构造环境。结果香山群的时代划归为中晚寒武世较合适;香山群主体是一套由板岩、细、粉砂岩和砂岩组成的浊积岩系,其砂岩类型主要是长石石英砂岩、细粒石英砂岩和粉砂质石英砂岩,前寒武纪变沉积岩和花岗片麻岩为主要碎屑来源和物源区组成;砂岩的岩石地球化学特征指示香山群属发育在被动大陆边缘斜坡环境中的沉积物,火山岩岩石地球化学特征反映其应属大洋扩张构造环境下的大洋拉斑玄武岩系列。结论香山群形成于伸展构造背景下的被动大陆边缘中的大陆斜坡和深海平原环境。

Aim From the research of the record of deposition-magmtism in Xiangshan group, to discuss the tectonic environment of Xiangshan Group in the southwest edge of Ordos massif. To provide the evidence for the recovery and deciding of tectonic background of the southwest edge of Ordos Basin in Early Paleozoic. Methods Through the systematic research for the features of lithology, sedmentary petrography, the feature of earth chemistry of sandstone and feature of earth chemistry of volcanic rock of Xiangshan Group stratum, the tectonic environment formed by Xiangshan Group has been researched synthetically. Results It is more reasonable to classify the times of Xiangshan Group into the Middle-Late Cambrian. The main part of Xiangshan Group is turbidite series which is made up of slate, fine-grained sandstones, powder-grained sandstones and middle-grained sandstones. The main types of sandstones in Xiangshan Group are middle-grained feldspar-quartz sandstones, fine - grained quartz sandstones and pewder-grained quartz sandstones. The main fragment source and source areas component of Xiangshan Group sandstones are Precambrian metamorphic-sedmentary rock and granite-gneiss. The feature of earth chemistry of sandstones shows that Xiangshan Group belongs the deposit which developed in the slope environment of passive continental margin. The feature of earth chemistry of volcanic rock in Xiangshan Group reflects that it belongs to the series of oceanic tholeiite in oceanic spreading tectonic environment. Conclusion The record of depesition-magmatism of Xiangshan Group reflects that the environment of continental slope and deep ocean plain formed in the background of spreading tectonics.