南羌塘坳陷早侏罗系曲色组下部泥岩地球化学特征及意义

以南羌塘坳陷早侏罗系曲色组下部的泥岩为研究对象,对其进行地球化学的研究。微量元素分析结果表明,曲色组泥岩沉积有较多的陆源物质,且Cr/Zr、Th/Sc、Th/U、Rb/Sr的值反映了泥岩物源区具有浅源、长英质、风化较严重的特点。稀土元素特征表明泥岩重稀土较轻稀土元素富集,具有轻微的Ce与Eu的负异常。通过Ceanom、V/(Ni+V)与CIA的值判断泥岩沉积时处于缺氧的沉积环境,且当时处于温暖潮湿的气候。通过La-Th-Sc和Th-Co-Zr/10物源区构造判别图,再结合La/Th的值与Hf的含量,判断曲色组泥岩的物源区构造背景以大陆岛弧为主,且兼具大陆边缘构造的特征。

Geochemical Characteristics and Significance of Mudstone in Bottom of Quse Formation in Early Jurassic,South Qiangtang Depression

The trace elements of mudstone in bottom of Quse Formation of Early Jurassic, South Qiangtang depression, are analyzed for discussing the sedimentary environment, source provenance and tectonic background of sedimentary rocks. The result shows that the typical continental origin elements (such as zirconium, scandium) are much richer than average crustal argillite, which means the mudstone deposited much terrigenous. Furthermore,the elements ratios of Cr/Zr, Th/Sc, Th/U, Rn/Sr, Cr/Th of Quse Formation indicate that the sediment sources are seriously weathered superficial felsicmaterials. The Characteristics of rare earth elements indicate that mudstone display LREE-enriched type in study area, were characterized by slight negative Ce anomalies and negative Eu anomalies.According to the means of Ceanom ,CIA and the ratio of V/(V+Ni), the marine depositional condition was in anoxic environment with the ancient climate of warm and humid. The tectonic environment distinguish diagram of La-Th-Sc, Th-Co-Zr/10, and relation diagram of La/Th and Hf, all these indicate that source material of Quse Formation in South Qiangtang depression are mainly from continental arc environment, but some material of passive continental margin environment also participate in it.