鄂尔多斯盆地西缘宁东地区侏罗系含铀地层元素地球化学特征

Elemental geochemical characteristics of Jurassic uranium-bearing strata in Ningdong area, western Ordos basin

沉积岩的地球化学特征记录了岩石沉积时的重要地质信息,是研究沉积古环境、源区构造背景及源岩属性的有效手段。采用X衍射荧光光谱(XRF)和等离子体质谱仪(ICP-MS)对鄂尔多斯盆地西缘宁东地区中侏罗统直罗组下段地层砂岩和泥岩样品的主、微量元素及稀土元素含量进行测试分析,旨在对其沉积古环境进行恢复,并对其源区构造背景、源岩属性等特征进行综合研究。研究表明:Sr含量、Sr/Cu值、V/(V+Ni)值、U/Th值、化学蚀变指数(CIA)等地球化学指标综合指示出研究区直罗组下段地层沉积古气候为半干旱–半湿润气候,古水体环境为富氧的淡水环境。根据稀土元素(REE)特征分析,推测研究区直罗组下段地层物源主要来自盆地西北部的阿拉善古陆,源岩岩性主要为片麻岩、石榴石浅粒岩、变不等粒石英砂岩和变中细粒石英砂岩。源区构造背景主要为大陆岛弧,与大洋岛弧也有一定关联。

The geochemical characteristics of sedimentary rocks record important geological information during the process of rock deposition,are an effective tool for the study of the paleoenvironment,the tectonic setting and the attributes of provenance.This paper aims to the comprehensive study of the paleoenvironment,the tectonic setting and provenance attribute of lower section of Zhiluo Formation by testing and analyzing the content of major elements,trace elements,and rare earth elements of the sandstone and mudstone samples collected from the lower section of Middle Jurassic Zhiluo Formation in the eastern margin of Ordos basin using the method of XRF and ICP-MS.The research indicates that Sr content,Sr/Cu ratio,V/(V+Ni)ratio,U/Th ratio,and CIA as well as other geochemical indexes suggest the semi-arid and semi-humid paleoclimate of lower section of Zhiluo Formation,and the oxygen enrichment-secondary oxygen enrichment freshwater environments as the paleo-water conditions;The rare earth feature proves that the provenances of lower section of Zhiluo Formation may be mainly the Alashan ancient land in the northwest of the basin.The provenance lithology is mainly made up of gneiss,garnet shallow rock,unequal grain quartz sandstone and medium-grained quartz sandstone.The tectonic setting of provenance area is mainly related to the continental island arc,and the oceanic island arc.