鄂尔多斯盆地塔然高勒地区直罗组砂岩源区构造背景与物源分析

Tectonic Setting and Provenance Analysis of Zhiluo Formation Sandstone of Tarangaole Area in the Ordos Basin

目前关于鄂尔多斯盆地塔然高勒地区直罗组沉积期物源和区域沉积-构造背景等问题尚缺研究,在一定程度上制约了直罗组物源变化的整体评价.对塔然高勒地区含铀层位直罗组下段砂岩进行了岩石地球化学、碎屑锆石U-Pb测年研究.结果显示,研究区直罗组下段源区岩石类型主要为长英质沉积岩和少量中性岩浆岩;源岩构造背景为活动大陆边缘-大陆边缘弧环境.综合微量、稀土元素特征和获得的锆石U-Pb定年数据,认为塔然高勒地区直罗组的物源主要来自大青山-乌拉山等地区的孔兹岩、TTG片麻岩、麻粒岩和镁铁质-超镁铁质层状侵入岩以及阴山地区形成于华力西期-印支期-燕山期的岩浆岩,直罗组下段砂体展布特征清楚地反映了研究区及相邻铀矿床由北向南的物源供给方向;研究区直罗组下段发现的三叠纪碎屑锆石表明三叠纪时期直罗组下段沉积时印支期侵入岩已被抬升至地表提供了物源,直罗组下段上亚段的年轻物源组分比例比下亚段的大.

Zhiluo Formation is located in Tarangaole area of the Ordos Basin and the research on the provenance and regional sedimentary structural setting remains weak,which restricts the overall evaluation of provenance change of Zhiluo Formationto some extent.Geochemical analysis and zircon U-Pb dating of sandstone in the lower Zhiluo Formation of uranium bearing horizon in Tarangaole area are applied in this paper.The results show that source rocks of the lower part of Zhiluo Formation are mainly felsic sedimentary rocks and few neutral magmatic rocks,and the tectonic setting of which is the active continental margincontinental margin arc environment.Based on the characteristics of trace and rare earth elements and zircon U-Pb dating results,it is considered that the sources of Zhiluo Formation in study area are mainly from Konzite,TTG gneiss,granulite and maficultramafic layered intrusive rocks in Daqingshan-Wulashan area,and Variscan-Indosinian-Yanshanian period magmatic rocks of Yinshan area.The distribution of sandstones in the lower part of Zhiluo Formation clearly reflects the direction of source supply from north to south,the discovery of Triassic detrital zircons indicates that the Indosinian intrusive rocks have been uplifted bare surface to provide material source during the sedimentation of the lower part of Zhiluo Formation in Triassic,and the proportion of younger provenance components in the upper member is higher than that in the lower member of the lower part of Zhiluo Formation.