峡东南华纪—震旦纪碎屑岩Ce同位素组成及地质意义

Cerium isotopic compositions of Nanhuan to Sinian clastic rocks in Eastern Three Gorges,South China,and their geological significance

元素La和Ce同属低活动性的稀土元素,能够对碎屑岩物源进行示踪。但目前尚缺乏对碎屑岩LaCe同位素体系的研究。本文以峡东泗溪南华纪—震旦纪碎屑岩为研究对象,进行了Ce同位素组成分析。结果显示：这些碎屑岩的138 Ce/142 Ce比值为0.022 583 2~0.022 587 8,εCe（t）值变化于1.06~6.13,整体上呈逐渐升高的演化特征,并与εNd（t）值呈耦合关系。结合碎屑岩Nd同位素分析结果认为,峡东南华纪—震旦纪碎屑岩的主要来源,以古元古代—中元古代甚至更老的地壳岩石为主,并存在幔源初生地壳物质加入。

Lanthanum and cerium are low mobile rare earth elements, which can be used to trace the provenance of elastics, but there is tack of systematic research on the La-Ce isotopes of elastics. This paper reports the Ce isotopic compositions of Nanhuan-Sinian elastic rocks in Sixi, Eastern Three Gorges. These elastic rocks have 138Ce/142 Ce values of 0. 0225832 to 0. 0225878, and show an increasing trend of Ce （t） values from 1.06 to 6. 13, which coupled with the end （t） values. Combined with Nd isotopec compositions of the elastic rocks, it is suggested that the main provenance of Nanhuan-Sinian elastic rocks in Sixi, Eastern Three Gorges were from the Paleoproterozoic - Middle Proterozoic and even older crustal rocks and mixing with juvenile crustal rocks in different degrees.