Post‐Miocene Erosion in Central Nepal Controlled by Midcrustal Ramp Position, Duplex Growth, and Dynamically Maintained Elastic Strain. Issue 12 (25th December 2020)

• Record Type: Journal Article
• Authors: Johnston, S. N.; Cannon, J. M.; Copeland, P.
• Is Part Of: Tectonics. Volume 39:Issue 12(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-12-25
• Subjects: erosion -- Himalayas -- central Nepal -- Main Himalayan Thrust -- elastic strain; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1029/2020TC006291
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: To better understand what drives erosion in central Nepal, we have mapped regions of preferential erosion by comparing modern detrital muscovite 40 Ar/ 39 Ar data to bedrock data from the Narayani river catchment and two subcatchments in central Nepal. We compare our pattern of erosion to erosion patterns from previous studies. Each shows a zone of preferential erosion from 5 km south to 20 km north of the Main Central Thrust (MCT). Peak erosion occurs in a 5‐km‐wide, orogen‐parallel band, north of the MCT, overlapping proposed ramps in the Main Himalayan Thrust (MHT). This location of peak erosion is consistent with the interpretation that erosion is tectonically driven. Although peak erosion is spatially coincident with the interpreted MHT ramps, the zone of enhanced erosion extends north of the ramps' downdip limits suggesting that an additional driver of rock uplift is at work. This can be explained by a duplex growing along the ramp back‐tilting and uplifting older duplex faults. This region also coincides with a dynamically supported bulge in the High Himalaya where a reservoir of elastic strain appears to be maintained over numerous seismic cycles further enhancing erosion. Key Points: Central Nepal has a 25 km zone of increased erosion above previous interpretations of the MHT ramp Erosion in central Nepal has remained focused in a central, orogen‐parallel band for 2–4 Myr Erosion is controlled by the position of a midcrustal ramp in the MHT, active duplexing, and a dynamically maintained elastic bulge