期刊
JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE
卷 121, 期 2, 页码 294-319出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/2015JF003508
关键词
cosmogenic radionuclides; landscape evolution models; erosion rates; fluvial geomorphology; Bhutan Himalaya; tectonics
资金
- National Science Foundation Tectonics Program [EAR 0708714]
- joint Tectonics and Geomorphology and Landuse Dynamics Programs grant [EAR 1049888]
Prior studies have proposed tectonic and climatic mechanisms to explain surface uplift throughout the Bhutan Himalaya. While the resulting enigmatic, low-relief landscapes, elevated above deeply incised canyons, are a popular setting to test ideas of interacting tectonic and climatic forces, when and why these landscapes formed is still debated. We test the idea that these landscapes were created by a spatially variable and recent increase in rock uplift rate associated with the formation of structural duplexes at depth. We utilize a new suite of erosion rates derived from detrital cosmogenic nuclide techniques, geomorphic observations, and a landscape evolution model to demonstrate the viability of this hypothesis. Low-relief landscapes in Bhutan are eroding at a rate of similar to 70m/Ma, while basins from surrounding steep landscapes yield erosion rates of similar to 950m/Ma, demonstrating that this portion of the range is in a transient period of increasing relief. Applying insights from our erosion rates, we explore the influence of an active duplex on overlying topography using a landscape evolution model by imposing a high rock uplift rate in the middle of a mountain range. Our simulations show that low-relief landscapes with thick alluvial fills form upstream of convex knickpoints as rivers adjust to higher uplift rates downstream, a pattern consistent with geologic, geomorphic, and thermochronometric data from Bhutan. With our new erosion rates, reconstructed paleo-river profiles, and landscape evolution simulations, we show that the low-relief landscapes were formed in situ as they were uplifted similar to 800m in the past similar to 0.8-1Ma.
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