桂西上二叠统合山组锂超常富集黏土岩的物源分析与地质意义

Provenance analysis and geological significance of Li-rich claystone in Upper Permian Heshan Formation,western Guangxi

以桂西平果地区上二叠统合山组铁铝岩、富锂黏土岩为研究对象,运用(MC-)LA-ICP-MS对样品进行碎屑锆石U-Pb定年和原位Hf同位素组成分析,结合铁铝岩碎屑锆石年龄特征,揭示富锂黏土岩的碎屑物质来源。铁铝岩样品,碎屑锆石主要年龄峰值为~430 Ma,次要峰值为~258 Ma;富锂黏土岩样品(主要化学成分为SiO_(2)30.5%、 Al_(2)O_(3) 34.2%、 Fe_(2)O_(3)^(T)15.2%、 Li 981×10^(-6)),碎屑锆石呈单一年龄峰值(~258 Ma),对应的ε_(Hf)(t)为-9.7~+11.4,与岛弧岩浆锆石ε_(Hf)(t)组成类似,表明其物源主要为古特提斯二叠纪岩浆弧相关的酸性岩。桂西地区铝土矿在时空上物源存在差异,反映了岩相古地理格局对成矿起重要控制作用。

The detrital zircon U-Pb dating and in situ Hf isotopic compositions were analysed using(MC-)LAICP-MS on the ferrallite and Li-rich claystone of the Upper Permian Heshan Formation in Pingguo,western Guangxi.Together with available detrital zircon U-Pb ages of ferrallite,this study reveals the provenance of the Li-rich claystone.Analytical results show that the U-Pb ages of detrital zircons from ferrallite are mainly concentrated at~430 Ma,along with a subordinate peak at~258 Ma.In contrast,the Li-rich claystone(with chemical compositions of SiO_(2)30.5%,Al_(2)O_(3)34.2%,Fe_(2)O_(3)^(T)15.2%,Li 981×10^(-6))shows the age peak at~258 Ma,with corresponding zircon ε_(Hf)(t)of-9.7 to+11.4,which are similar to those of island arc magma-derived zircons.This indicates that the Li-rich claystone was mainly sourced from the Permian felsic igneous rocks related to Paleo-Tethys arc magmatism.Tempo-spatial variations of provenances of bauxite-bearing rocks of the Heshan Formation suggest that paleogeographic variations play an important role in the formation of bauxite in western Guangxi.