Along-strike changes in the geometry of the Main Himalayan Thrust in the northwestern Himalaya: Insights from erosion rates, river profiles, and landscape morphology.
Abstract
Geodetic models suggest that much of the convergence across the Himalaya ( 20 mm yr-1) is taken up on the Main Himalayan Thrust, the main decollement beneath the Himalayan wedge. In Central Nepal and the majority of Northwest India, a number of geomorphic, geophysical and seismological datasets indicate that this decollement exhibits a ramp-flat geometry in cross section and continues uninterrupted for 100s of km along strike. In this study, we use basin-wide erosion rates from cosmogenic Be-10 concentrations and longitudinal profile analysis to outline a potential large scale change in the geometry of this decollement at longitude 77°E. The physiography in the areas to the east of 77° appear similar to that observed along much of the Himalaya. Here, hillslope relief, erosion rates, topography, and river channels (ksn <200) remain relatively low in the areas to the south above the decollement flat, but they increase northward due to higher rock uplift rates above the decollement ramp. To the west of 77°, however, basin-wide erosion rates, channel steepness (ksn <50), and hillslope angles decrease significantly along-strike above the presumed location of the decollement flat. These decreases occur coincident with a prominent, km-scale embayment in the Main Boundary Thrust. These data suggest that the Main Boundary Thrust could merge along strike with the ramp in the Main Himalayan Thrust at this location, and could mark a significant lateral change in active fault geometry. This along-strike change in fault geometry could have implications for how large (Mw>8) earthquake ruptures are partitioned within this region.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP11B1003M
- Keywords:
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- 1130 Geomorphological geochronology;
- GEOCHRONOLOGYDE: 8040 Remote sensing;
- STRUCTURAL GEOLOGYDE: 8107 Continental neotectonics;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS