Active out-of-sequence thrust faulting in the central Nepalese Himalaya

Abstract

Recent convergence between India and Eurasia is commonly assumed to be accommodated mainly along a single fault—the Main Himalayan Thrust (MHT)—which reaches the surface in the Siwalik Hills of southern Nepal1,2,3. Although this model is consistent with geodetic4,5, geomorphic6 and microseismic data7, an alternative model incorporating slip on more northerly surface faults has been proposed to be consistent with these data as well8,9,10. Here we present in situ cosmogenic 10Be data indicating a fourfold increase in millennial timescale erosion rates occurring over a distance of less than 2 km in central Nepal, delineating for the first time an active thrust fault nearly 100 km north of the surface expression of the MHT. These data challenge the view that rock uplift gradients in central Nepal reflect only passive transport over a ramp in the MHT. Instead, when combined with previously reported 40Ar–39Ar data9, our results indicate persistent exhumation above deep-seated, surface-breaking structures at the foot of the high Himalaya. These results suggest that strong dynamic interactions between climate, erosion and tectonics have maintained a locus of active deformation well to the north of the Himalayan deformation front.

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Figure 1: Geological setting.
Figure 2: Sampling locations and study area physiography.
Figure 3: Erosion rate and cooling-age data.

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Acknowledgements

We thank D. Burbank and P. Bierman for constructive reviews, which greatly improved the quality of the original manuscript, R. Finkel at LLNL for accommodating our samples at short notice, and B. Crosby, K. Ruhl, T. Schildgen, N. Wobus and Himalayan Experience for field assistance. The work was funded by NSF and NSF Continental Dynamics.

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Correspondence to Cameron Wobus.

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Wobus, C., Heimsath, A., Whipple, K. et al. Active out-of-sequence thrust faulting in the central Nepalese Himalaya. Nature 434, 1008–1011 (2005). https://doi.org/10.1038/nature03499

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