Pleistocene rapid decrease in extensional exhumation of the Diancang Shan implies tectonic changes in SE Tibet
Abstract
Changes in geodynamic processes significantly affect the evolution of mountain belts and are commonly manifested as abrupt changes in rates of exhumation. Such changes, however, have been rarely quantified during the Quaternary. For the few sites reported in the region (e.g., western and eastern Himalayan syntaxes), the exhumation rate generally increased, instead of decreased, during the Quaternary. Here, we report a Pleistocene rapid decrease in extensional exhumation of the Diancang Shan (DCS) in SE Tibet, located at the NW end of the dextral Red River fault (RRF). Normal faults develop on both sides of the DCS and its extensional exhumation has been argued to reflect the RRF's tectonic activity. We used exhumation estimates obtained from apatite fission track (AFT) and catchment-wide erosion rates based on 10Be concentrations to examine changes of exhumation on the millennial to million-year timescales. An elevation transect spanning 1.7 km-relief in central DCS shows AFT ages of 0.3-0.9 Ma, suggesting an apparent exhumation rate of 2.8 km/Ma (mm/yr). This rate is higher than, but of the same order as, previous estimate of exhumation over ~5 Myrs based on Ar-Ar thermochronometry. In comparison, five catchments across the DCS show watershed-averaged differential erosion rates of 0.07-0.21 mm/yr. These millennial-scale-averaged erosion rates are >10 times smaller than the million-year-averaged exhumation rates, suggesting a dramatic reduction in the DCS's exhumation rate. A climatic origin for this change is unlikely because Quaternary glaciation in this region should increase, instead of reduce, the erosion. We suggest that the change in exhumation rate is tectonic origin, and consistent with previous inference of a large decrease of the RRF's slip rates from ~5 mm/yr over 5-10 Myrs to ~1 mm/yr over ~50 kyrs. These together suggest a late Quaternary change for the geodynamics in SE Tibet that decelerated the RRF's activity and regional extension.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T51D0291S
- Keywords:
-
- 8011 Kinematics of crustal and mantle deformation;
- STRUCTURAL GEOLOGY;
- 8110 Continental tectonics: general;
- TECTONOPHYSICS;
- 8169 Sedimentary basin processes;
- TECTONOPHYSICS;
- 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS