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https://doi.org/10.5194/se-2020-172
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2020-172
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  13 Oct 2020

13 Oct 2020

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This preprint is currently under review for the journal SE.

Contrasting exhumation histories and relief development within the Three Rivers Region (Southeast Tibet)

Xiong Ou1, Anne Replumaz1, and Peter van der Beek2 Xiong Ou et al.
  • 1Institut des Sciences de la Terre (IsTerre), Université Grenoble Alpes, Grenoble, 38058, France
  • 2Institute of Geosciences, Potsdam University, Potsdam, 14476, Germany

Abstract. The Three Rivers Region in Southeast Tibet represents a transition between the strongly deformed zone around Eastern Himalayan Syntaxis and the less deformed southeast Tibetan plateau margin in Yunnan and Sichuan. In this study, we compile and model published thermochronologic ages for two massifs facing each other across the Mekong River in the core of the Three Rivers Region, by using the thermo-kinematic code Pecube to constrain their exhumation and relief development history. Modelling results for the low-relief, mean-elevation BaimaXueshan massif, east of the Mekong River, suggest regional rock uplift at a rate of 0.25 km/Myr since ~ 10 Ma, following slow exhumation at a rate of 0.01 km/Myr since at least 22 Ma. River incision accounts for only 15 % of the total exhumation in the BaimaXueshan. Exhumation since ~ 10 Ma is significantly higher (2.5 km) than that estimated (~ 0.23 km) for the most emblematic low-relief or relict surfaces of Eastern Tibet, which are characterized by apatite (U-Th)/He ages older than the collision age (> 50 Ma). We conclude that the BaimaXueshan massif, which shows younger ages (< 50 Ma) that record significant rock uplift and exhumation during the Neogene, cannot be classified as a relict surface despite its low relief. Modelling results for the high-relief, high-elevation Kawagebo massif, to the west of the Mekong, imply a similar contribution of Mekong River incision (20 %) to exhumation, but much stronger local rock uplift at a rate of 0.45 km/Myr since at least 10 Ma, accelerating to 1.86 km/Myr since 1.6 Ma. We show that the age-elevation profiles for three thermochronometers are best modeled by rock uplift on a kinked westward-dipping thrust striking roughly parallel to the Mekong River, with a steep shallow segment flattening out at depth. Thus, the strong differences in elevation and relief that characterize these massifs are linked to variable exhumation histories due to a strongly differing tectonic imprint.

Xiong Ou et al.

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Short summary
The low-relief, mean-elevation BaimaXueshan massif experienced slow exhumation at a rate of 0.01 km/Myr since at least 22 Ma, then regional rock uplift at a rate of 0.25 km/Myr since ~ 10 Ma. The high-relief, high-elevation Kawagebo massif shows much stronger local rock uplift related to the motion along a west-dipping thrust fault, at a rate of 0.45 km/Myr since at least 10 Ma, accelerating to 1.86 km/Myr since 1.6 Ma. Mekong River incision plays a minor role in total exhumation in both massifs.
The low-relief, mean-elevation BaimaXueshan massif experienced slow exhumation at a rate of...
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