Tectonic setting and provenance of the Xikang Group in the Guining area, West Sichuan Province: Constraints from geochemistry of clastic sedimentary rocks

The Xikang Group, distributed in the Guining area between the Changqiang Dome and Jianglang Dome in West Sichuan Province, is one set of low metamorphosed turbidite flysch.Based on the study of their petrological and geochemical characteristics of the clastic rocks, the provenance and affiliation were analyzed. The results show that the major elements of the sandstone, SiO₂ and P₂O₅, are similar to the upper crust, with relatively high CaO and MgO, while the contents of Al₂O₃, Fe₂O₃, K₂O and TiO₂ are relatively low.The Chondrite-normalized trace element spider diagram of clastic sedimentary rocks is "M"-shaped and inclined to the right, rich in Th, U, La, Nd, Zr, Sm and poor in K, Nb, Sr, P, Hf.The rare earth elements of the samples display obvious fractionation in light and heavy REE, strong enrichment in light REEs with medium negative Eu anomaly.The chemical alteration index (CIA) and composition variation index value (ICV) are both low, reflecting the weak weathering degree of the source area and the characteristics of rapid accumulation of sediments near source, which represents the first deposition of the active structural belt.The fingerprint discrimination diagram and trace element value show that the source of the Xikang Group in this area was felsic in upper crust.According to geochemical tectonic setting discrimination diagrams, the structural background of the clastic rocks is active continental margin and continental island arc.Based on the paleocurrent evidence of field investigation and the reconstruction of paleogeography, it is inferred that the provenance of the Xikang Group might have come from the Kangdian ancient land in the southeast direction, and have an affinity to the Yangtze Block.