Cenozoic multiple-phase tectonic evolution of the northern Tibetan Plateau: Constraints from sedimentary records from Qaidam basin, Hexi corridor, and Subei basin, northwest China

An integrated research of sedimentology, stratigraphy, and provenance analysis on eleven sedimentary sections from the Qaidam basin, Hexi Corridor, and Subei basin representing ∼36 km Cenozoic strata provides a detailed record of the northern Tibetan Plateau growth since the early Eocene. Sections are divided into three groups based on age, geological similarities, and geographical locations. Group One includes three early Eocene-late Miocene sections from the northern Qaidam basin; Group Two contains four sections along the Altyn Tagh fault (ATF) which preserve a complete stratigraphic record from the Oligocene to late Miocene; Group Three contains the four youngest sections investigated from the northeastern Qaidam basin and Hexi Corridor which preserve a record since the middle Miocene to Quaternary. Together, the sections reveal a multiple-phase tectonic history of the northern Tibetan Plateau. The punctuated history can be divided into four phases. (1) The Eocene Lulehe Formation from the northern Qaidam basin is interpreted as a synorogenic conglomerate deposited by high-gradient depositional systems. Strong unimodal paleocurrent towards the southwest, coarse lithology and distinct, recognizable clast types constrain the sediment source within the North Qaidam and South Qilian terranes, indicating activity on inferred thrust faults within the North Qaidam and South Qilian terranes in response to the initial India-Eurasia collision. The activity on these thrust faults continued through the late Eocene. (2) The early Oligocene conglomerate from Group Two formed in response to the sinistral transpression related to motion on the ATF, suggesting inception of substantial slip on the ATF in the early Oligocene in order to accommodate the continuing indentation of India into Eurasia. (3) Oligocene-early Miocene fine-grained fluvio-lacustrine sediments from Groups One and Two formed as the result of development of internal drainage systems in the Qaidam basin in response to the large-amplitude slip motion on the ATF. Paleocurrents collected from the Oligocene-early Miocene strata of Group One are northwest-directed, pointing towards the ATF, consistent with the pre-existing subsurface data showing the shift of depocenter from along North Qaidam and South Qilian terranes toward the ATF. (4) All eleven sections preserve a post-early Miocene upward-coarsening sequence, consistent with the extensive crustal shortening and topographic growth across the northern Tibetan Plateau