云南思茅盆地勐野井组碎屑岩矿物学、地球化学特征及古盐湖沉积环境演化  被引量:6

Mineralogical and Geochemical Characteristics of Detrital Rocks in the Mengyejing Formation and Evolution of the Sedimentary Environment of Paleolake in Simao Basin,Yunnan Province

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作  者:苗卫良[1,2] 马海州[1] 张西营[1] 石海岩 李永寿[1,2] 容志明 

机构地区:[1]中国科学院青海盐湖研究所盐湖地质与环境重点实验室,西宁810008 [2]中国科学院研究生院,北京100049 [3]青海省西海煤电有限责任公司,青海海北藏族自治州西海镇810200

出  处:《地质学报》2015年第11期2096-2107,共12页Acta Geologica Sinica

基  金:国家"973"计划项目第四课题"兰坪-思茅新生代残留盆地成钾条件;机理和后期演化"(编号:2011CB403004);国家自然科学基金青年基金项目(编号:41303029)资助的成果

摘  要:通过对云南思茅盆地勐野井钾盐矿区钻孔岩心的碎屑沉积物进行粘土矿物分析和元素地球化学分析探讨了研究区晚白垩世碎屑岩的物源属性及古盐湖沉积环境演化特征。粘土矿物组合特征及La/Th-Hf、La/Sc-Th/Co、La-Th-Sc图解,Cr/Th、Al2O3/TiO2比值等表明该孔碎屑岩的物源主要为长英质花岗闪长岩。主量元素活动性分析表明化学风化过程中随着粘土矿物的形成首先发生Ca和Na的淋失,K、Mg则在这一过程中呈富集态势,而Fe、Mn主要受物源限制而总体上表现为亏损。结合粘土矿物形成条件,认为研究区古盐湖经历了暖湿—暖干(成盐成钾期)—暖湿(淡化)的古气候转化过程。而粘土矿物组合受高盐极端环境与埋藏成岩作用影响显著,表现为成盐成钾期显著的伊利石化和绿泥石化作用。因此伊利石+绿泥石粘土矿物组合,结合富Mg绿泥石的相对含量,以及相应沉积阶段碎屑岩的MgO异常高值,可有效指示古盐湖成盐成钾的演化阶段。!Clay mineralogy and geochemistry of detrital sediment samples collected in a core of the Mengyejing Potash salt mining of Simao basin,Yunnan were used to evaluate the provenance and sedimentary environment evolution of paleolake.The clay mineral assemblages,La/Th-Hf,La/Sc-Th/Co,La-Th-Sc diagrams and values of Cr/Th,Al2O3/TiO2 indicate that the provenance of the detrital sediment is mainly granodiorites.And the major element results indicate that the formation of clay minerals is accompanied by leaching of Ca and Na first and enrichment of K and Mg.Fe and Mn,is deplete because of the limitations provenance.Combined with the formation conditions of clay minerals,we suggest that the paleolake experienced a variable paleoclimate evolution process which characterized by warm and wet to warm and dry(the stage of salt-forming and sylvite-forming)to warm and wet(the desalination stage).The hypersaline environment and burial diagenesis affected the clay mineral assemblages significantly,documented by the widespread occurrence of illitization and chloritization in core samples.Thus,the clay mineral assemblages of illite+chlorite,combined with the abundance of Mg-rich chlorite and the abnormally high value of MgO of detrital sediments at the corresponding stage are indictive of the evolution of salt-forming and sylvite-forming stage.

关 键 词:晚白垩世 碎屑岩 粘土矿物 地球化学 物源 成盐成钾 云南思茅盆地 

分 类 号:P619.211[天文地球—矿床学] P512.2[天文地球—地质学]

 

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