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

Abstract

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 detrital-zircon 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 ~1800 Ma and ~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.