Abstract:

Through a comprehensive study on the major elements, trace elements and rare earth elements of fluvial sand of Triassic Xikang Group in Ruoergai area in Sichuan Province, this paper found that the fluvial sand of this area has the same contents of SiO2, P2O5 and MnO as that in PAAS. It is enriched in Na₂O, CaO and poored in Al₂O₃, Fe₂O₃, MgO, K₂O and TiO₂.The content of trace element W is far greater than the supracrustal abundance. The contents of Nb and Ta are far lower than the supracrustal abundance, but it is about same as lower crustal abundance. The contents of Sc are lower than the supracrustal abundance. Petrogenic element Sr is a little higher than crustal abundance. The capacity of rare earth elements is relatively higher. The average value is 133.97×10^-6, which is close to 112×10^-6-the capacity of rare earth elements in the crust. Light rare earth elements are richer than heavy rare earth elements. It has medium negative europium anomaly. The distribution curves of rare earth elements show a consistent rightward declined light rare earth elements enrichment pattern. It is thought that its geochemical characteristics are similar with that of continental arc and passive continental margin sediment. To sum up other geological data, it is concluded that Kangdian old land is a possible provenance region of fluvial sand of Triassic Xikang Group in Ruoergai area.

Key words: Ruoergai area, Triassic, geochemistry, provenance, paleoweathering, Sichuan