Characteristics and provenance analysis of the Upper Tertiary Xujiahe Formation sandstone in the middle part of West Sichuan depression

Abstract：By means of thin section, SEM, quartz cathodoluminescence and X-RD analysis, the authors studied the mineral composition and texture of the Upper Tertiary Xujiahe Formation sandstone in the middle part of West Sichuan depression, analyzed the composition maturity and texture maturity and, according to the scheme of genesis-composition, classified the sandstone. Based on an analysis of characteristics of sandstone and clastic components as well as the regional tectonic setting, the authors also investigated the direction of the sources. The results show that there exist multi-provenances of upper Triassic Xujiahe Formation in the middle part of west Sichuan depression, as evidenced by the Dickinson discriminating diagrams of modal composition. Mineral assemblages and cathodoluminescence colors of quartz suggest that the mother rock of xu-2 and xu-3 period was acidic rock and that of xu-4 period is sedimentary rock in Dayi, the mother rock of Xujiahe period is mainly composed of sedimentary rock and metamorphic rock.. The results show that the provenance of xu-2 period might have come from northern Longmenshan uplift, the south island chain of Longmenshan and Kangdian old land. The provenance of xu-3 period might be not different from that of xu-2 period. The provenance of xu-4 period and the following periods might have come from Longmenshan old land. Generally speaking, the provenance of the area was controlled by the evolution of Longmenshan.