Cosmogenic 38Ar in feldspar: A new tool for exposure studies in stable landscapes

Abstract

The geometry and evolution of fluvial systems are thought to be related to surface uplift. In eastern Tibet, rivers exhibit peculiar drainage patterns but how these patterns were established and their connection with the plateau uplift are still under debate. Here, we use detrital zircon U-Pb dating, bedrock (U-Th)/He thermochronometry, topographic analysis and numerical modeling to explore the paleo-drainage pattern of the Dadu and Anning Rivers, eastern Tibet. Our detrital data indicate that the Pliocene sources of sediments to the Anning River are different from the modern ones and they include a source similar to that of the modern Dadu River, implying a paleo-connection between the Dadu and the Anning Rivers and a subsequent cutoff of this connection after the deposition of the Pliocene sediments. Bedrock thermochronometric data along the Dadu River reveal rapid cooling at ∼10 Ma and a possible enhanced cooling at ∼2 Ma, which we interpret as a response to the regional plateau uplift in eastern Tibet and to the Dadu-Anning capture, respectively. Combined with topographic analysis and numerical modeling, our results indicate an Early Pleistocene capture between the Dadu and Anning Rivers, resulting in the changes in the sediment sources of the Anning River, enhanced incision of the Dadu, and the transience of the Dadu River profile. The Dadu-Anning capture is related to the motion along the active sinistral strike-slip Daliangshan fault that locally disrupts the river network. This event does not date the plateau uplift; rather, it indicates how river reorganization can effectively enhance river incision and affect landscape development independently from regional-scale uplift.