Cenozoic basin evolution of the central Tibetan plateau as constrained by U-Pb detrital zircon geochronology, sandstone petrology, and fission-track thermochronology

We conduct sandstone-composition analysis, U-Pb detrital-zircon dating, and apatite fission-track thermochronology to determine how basin development was associated with the Cenozoic deformation across central Tibet. Our results are consistent with a two-stage basin development model: first a single fluvial-lacustrine system formed (i.e., Paleo-Qaidam basin) in between two thrust belts (i.e., the Fenghuoshan and Qilian Shan thrust belts) in the Paleogene, which was later partitioned into two sub-basins in the Neogene by the Kunlun transpressional system and its associated uplift. The southern sub-basin (i.e., Hoh Xil basin) strata have detritalzircon age populations at 210-300 Ma and 390-480 Ma for the Eocene strata and at 220-310 Ma and 400-500 Ma for the early Miocene strata; petrologic analysis indicates that the late Cretaceous-Eocene strata were recycled from the underlying Jurassic rocks. The northern sub-basin (i.e., Qaidam basin) strata yield detrital-zircon age clusters at 210-290 Ma and 370-480 Ma in the Eocene, 220-280 Ma and 350-500 Ma in the Oligocene, 250-290 Ma and 395-510 Ma in the Miocene, and 225-290 Ma and 375-480 Ma in the Pliocene. Proterozoic ages of the detrital zircon are most useful for determining provenance: the pre-Neogene Hoh Xil and Qaidam strata all contain the distinctive age peaks of similar to 1800 Ma and similar to 2500 Ma from the Songpan-Ganzi terrane south of the Kunlun fault, whereas detrital zircon of this age is absent in the Neogene Qaidam strata suggesting the emergence of a topographic barrier between the two basins. This inference is consistent with our fission-track thermochronological data from the Eastern Kunlun Range that suggest rapid cooling within the range did not start until after 30-20 Ma. Our new data support the Paleo-Qaidam hypothesis that requires the Hoh Xil and Qaidam basins were parts of a single Paleogene basin bounded by the Qilian Shan and Fenghuoshan thrust belts.