Timing of Xunhua and Guide basin development and growth of the northeastern Tibetan Plateau, China

Abstract The X unhua, G uide and T ongren intermontane basin system in the NE T ibetan P lateau, situated near the X ining basin to the N and the L inxia basin to the E, is bounded by thrust fault‐controlled ranges. These include to the N, the R iyue S han, L aji S han and J ishi S han ranges, and to the S the northern West Q inling S han ( NWQ ). An integrated study of the structural geology, sedimentology and provenance of the C enozoic X unhua and G uide basins provides a detailed record of the growth of the NE T ibetan P lateau since the early E ocene. The X ining G roup ( ca . 52–21 Ma) is interpreted as consisting of unified foreland basin deposits which were controlled by the bounding thrust belt of the NWQ . The X unhua, G uide and X ining subbasins were interconnected prior to later uplift and damming by the L aji S han and J ishi S han ranges. Their sediment source, the NWQ , is constrained by strong unidirectional paleocurrent trends towards the N, a northward fining lithology, distinct and recognizable clast types and detrital zircon ages. Collectively, formation of this mountain–basin system indicates that the T ibetan P lateau expanded into the NWQ at a time roughly coinciding with E ocene to earliest M iocene continental collision between I ndia and E urasia. The G uide G roup ( ca . 21–1.8 Ma) is inferred to have been deposited in the separate X unhua, G uide and T ongren broken foreland basins. Each basin was filled by locally sourced alluvial fans, braided streams and deltaic‐lacustrine systems. Structural, paleogeographic, paleocurrent and provenance data indicate that thrust faulting in the NWQ stepped northward to the L aji S han from ca . 21 to 16 Ma. This northward shift was accompanied by E–W shortening related to nearly N–S‐striking thrust faulting in J ishi S han after 11–13 Ma. A lower P leistocene conglomerate (1.8–1.7 Ma) was deposited by a through‐flowing river system in the overfilled and connected G uide and X unhua basins following the termination of thrust activity. All of the basin–mountain zones developed along the T ibetan P lateau's NE margin since I ndian– T ibetan continental collision may have been driven by collision‐induced basal drag of old slab remnants in the manner of N‐dipping and flat‐slab subduction, and their subsequent sinking into the deep mantle.