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鄂尔多斯盆地志丹地区安定组泥灰岩地球化学特征及古环境意义
投稿时间:2020-02-23  修订日期:2020-04-16  点此下载全文
引用本文:
DOI:10.19762/j.cnki.dizhixuebao.2020068
摘要点击次数: 58
全文下载次数: 63
作者单位E-mail
汤超 中国地质调查局天津地质调查中心 中国地质调查局铀矿地质重点实验室 tjtangchao@163.com 
肖鹏 中国地质调查局天津地质调查中心 中国地质调查局铀矿地质重点实验室  
魏佳林 中国地质调查局天津地质调查中心 中国地质调查局铀矿地质重点实验室  
徐增连 中国地质调查局天津地质调查中心 中国地质调查局铀矿地质重点实验室  
刘华健 中国地质调查局天津地质调查中心 中国地质调查局铀矿地质重点实验室  
赵丽君 中国地质调查局天津地质调查中心  
中文摘要:通过对鄂尔多斯盆地志丹地区安定组顶部泥灰岩系统的岩石学和地球化学分析,研究了安定组沉积末期湖盆的古盐度、氧化还原环境、古气候及物源区背景。结果表明:安定组泥灰岩主要由方解石和白云石组成,其中方解石含量26.5%~68.5%,平均42.5%,白云石含量10.1%~40.5%,平均25.3%;岩石具有较高的Sr丰度、Sr/Ba比值,指示沉积时水体盐度较高;碳氧同位素变化范围不大,δ13CPDB为-3.5‰~2.2‰,平均0.55‰,δ18OPDB为-6‰~-1.2‰,平均-3.87‰,接近咸水湖碳酸盐沉积物,Z值范围为119.53~130.01,平均为126.51,显示安定组泥灰岩段形成于湖水咸化期;化学蚀变指数CIA及Sr/Cu 、SiO2/Al2O3综合指示泥灰岩的物源区所受化学风化并不强烈,沉积于半干旱炎热的气候;氧化还原环境指标V/Cr、V/(V+Ni)比值及敏感金属元素U、Mo高度富集等特征指示泥灰岩沉积时的古水体条件整体处于还原环境;La/Yb-∑REE和La/Sc-Co/Th源岩属性判别图解显示泥灰岩主要沉积物源以长英质岩石为主,并混合有中-基性岩浆岩,与鄂尔多斯盆地北部阴山地区的古元古代变质岩系具有一定的亲源性。安定组末期半干旱炎热的气候条件,有利于蚀源区铀元素的活化迁移和含氧含铀流体形成和湖盆中铀的原始富集沉淀,为鄂尔多斯盆地大规模砂岩型铀成矿作用提供了重要条件。
中文关键词:安定组  泥灰岩  地球化学  古环境  鄂尔多斯盆地
 
Geochemical characteristics and paleoenvironmental significance of marls from Anding Formation in Zhidan area, Ordos Basin
Author NameAffiliationE-mail
tangchao Tianjin center, China Geological Survey Key Laboratory of Uranium Geology, China Geological Survey tjtangchao@163.com 
Xiao Peng Tianjin center, China Geological Survey Key Laboratory of Uranium Geology, China Geological Survey  
Wei Jialin Tianjin center, China Geological Survey Key Laboratory of Uranium Geology, China Geological Survey  
Xue Zenglian Tianjin center, China Geological Survey Key Laboratory of Uranium Geology, China Geological Survey  
Liu Huajian Tianjin center, China Geological Survey Key Laboratory of Uranium Geology, China Geological Survey  
Zhao Lijun Tianjin center, China Geological Survey  
Abstract:Based on the systematic petrological and geochemical analysis of the marls at the top of Anding Formation in Zhidan area of Ordos Basin, the paleo-salinity, redox environment, paleoclimate and provenance background at the end of the deposition period of Anding Formation were studied. The results show that the marsl of the Anding Formation is mainly composed of calcite and dolomite, of which calcite content is 26.5% ~ 68.5%, with an average of 42.5%, and dolomite content is 10.1% ~ 40.5%, with an average of 25.3%. The rock has a high Sr abundance and Sr / Ba ratio, indicating that the water salinity is high during sedimentation. The range of carbon and oxygen isotopes is not large, δ13CPDB is -3.5 ‰ ~ 2.2 ‰, with an average of 0.55 ‰, δ18OPDB is -6 ‰ ~ -1.2 ‰, with an average of -3.87 ‰, which is close to the saltwater carbonate deposits, and the Z value range is 119.53 ~ 130.01, with an average of 126.51, indicating that the marl section of the Anding Formation was formed during the lake salinization period.The chemical alteration index CIA and Sr / Cu, SiO2 / Al2O3 comprehensively indicate that the chemical weathering of the source area of marl is not strong, and it is deposited in a semi-arid and hot climate. The redox environmental indicators V / Cr, V / (V + Ni) ratio, and the high enrichment of sensitive metal elements U and Mo indicate that the paleowater conditions during the deposition of marl are generally in the reducing environment. La/Yb-∑REE and La/ Sc-Co/Th source rock attribute discrimination diagrams show that the main source of marl sedimentary rocks is dominated by felsic rocks, mixed with medium-basic magmatic rocks, which has a certain affinity with Paleoproterozoic metamorphic rock series in Yinshan area of northern Ordos. The semi-arid and hot climatic conditions at the end of the Anding Formation are conducive to the activation and migration of uranium elements, the formation of oxygen-containing uranium-containing fluids in the source area and the original enrichment and precipitation of uranium in the lake basin, which provides important conditions for large-scale sandstone-type uranium mineralization in the Ordos Basin.
keywords:Anding  Formation, marls, geochemistry, paleoenvironment, Ordos Basin
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