Tectonic evolution of the Himalayan thrust belt in western Nepal: Implications for channel flow models

Robinson, Delores M.; DeCelles, Peter G.; Copeland, Peter

doi:10.1130/b25911

Cited by 75 publications

(228 citation statements)

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“…For the sake of discussion, we refer to the northern topographic step as PT2-N and the southern as PT2-S. The latter coincides roughly with the southern margin of the Miocene-aged Main Central thrust sheet, preserved locally as the Dadeldhura (or, to some authors, the Karnali) klippe (Robinson et al, 2006). The escarpment at PT2-N is of a similar magnitude as the southern, with mean elevations rising from ~3 km to ~5 km.…”

Section: Resultsmentioning

confidence: 96%

“…Footwall accretion has been invoked to explain the present structural geometry of the orogen (e.g., DeCelles et al, 1998;Robinson et al, 2006;Cannon and Murphy, 2014) and the distribution of cooling ages across the range (e.g., Herman et al, 2010). The Himalaya of western Nepal may be an example where footwall accretion is actively participating in mountain building and causing the locus of internal deformation to shift ~65 km toward the tip of the orogenic wedge.…”

Section: Discussionmentioning

confidence: 99%

“…1), commonly referred to as PT2, has garnered much attention as indicative of a key tectonic change (e.g., Hodges et al, 2001). This informal boundary has been variably attributed to rapid rock uplift over a steeper ramp along the Main Himalayan thrust linking gentler sections beneath the Lesser Himalaya to the south and the Tibetan Plateau to the north (e.g., Cattin and Avouac, 2000), although Berger et al, 2004Robinson et al, 2006Decelles et al, 2001 (1995-1996, 1996-1997, and 1998-1999 Along-strike changes in thrust geometry between central and western Nepal | SHORT RESEARCH some argue for out-of-sequence thrusting at the foot of the Greater Himalaya, (e.g., Wobus et al, 2003). Geodetic, geomorphic, and thermochronologic studies confirm that a zone of rapid uplift and exhumation lies immediately north of PT2, in contrast to the relatively low rates within the Lesser Himalaya (Jackson and Bilham, 1994;Lavé and Avouac, 2001;Copeland et al, 1991;Blythe et al, 2007).…”

Section: Geologic Settingmentioning

confidence: 99%

“…Bedrock geology in western Nepal was compiled from mapping by Fuchs (1977), Arita et al (1984), DeCelles et al (1998), DeCelles et al (2001, Murphy et al (2002), Murphy and Copeland (2005), and Robinson et al (2006). Locations of recently active faults were compiled from a combination of data from Yin (2009), Murphy et al (2014), and our own mapping.…”

Section: Geology and Seismicitymentioning

confidence: 99%

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Along-strike changes in Himalayan thrust geometry: Topographic and tectonic discontinuities in western Nepal

2015

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Geodetic and seismologic studies support a tectonic model for the central Himalaya wherein ~2 cm/yr of Indo-Asian convergence is accommodated along the primary décollement under the range, the Main Himalayan thrust. A steeper midcrustal ramp in the Main Himalayan thrust is commonly invoked as driving rapid rock uplift along a range-parallel band in the Greater Himalaya. This tectonic model, developed primarily from studies in central Nepal, is commonly assumed to project along strike with little lateral variation in Main Himalayan thrust geometry or associated rock uplift patterns. Here, we synthesize multiple lines of evidence for a major discontinuity in the Main Himalayan thrust in western Nepal. Analysis of topography and seismicity indicates that west of ~82.5°E, the single band of steep topography and seismicity along the Main Himalayan thrust ramp in central Nepal bifurcates around a high-elevation, low-relief landscape, resulting in a two-step topographic front along an ~150 km segment of the central Himalaya. Although multiple models could explain this bifurcation, the full suite of data appears to be most consistent with a northward bend to the Main Himalayan thrust ramp and activation of a young duplex horse to the south. This poorly documented segmentation of the Main Himalayan thrust has important implications for the seismogenic potential of the western Nepal seismic gap and for models of the ongoing evolution of the orogen.

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Section: Resultsmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

Section: Geologic Settingmentioning

confidence: 99%

Section: Geology and Seismicitymentioning

confidence: 99%

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Along-strike changes in Himalayan thrust geometry: Topographic and tectonic discontinuities in western Nepal

2015

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“…1 of Kohn et al 2001). DeCelles et al (2001) and Robinson et al (2003Robinson et al ( , 2006 mapped two thrust sheets structurally beneath the Main Central Thrust in western Nepal, the higher Dadeldhura and lower Ramgarh thrust sheets. They failed to locate a discrete thrust at the position of the Main Central Thrust and inferred its presence from extrapolation along strike in the Karnali Valley.…”

Section: Metamorphic Isograds and The Main Central Thrustmentioning

confidence: 99%

Defining the Himalayan Main Central Thrust in Nepal

Searle

Law

Godin

et al. 2008

JGS

298

247

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An inverted metamorphic field gradient associated with a crustal-scale south-vergent thrust fault, the Main Central Thrust, has been recognized along the Himalaya for over 100 years. A major problem in Himalayan structural geology is that recent workers have mapped the Main Central Thrust within the Greater Himalayan Sequence high-grade metamorphic sequence along several different structural levels. Some workers map the Main Central Thrust as coinciding with a lithological contact, others as coincident with the kyanite isograd, up to 1-3 km structurally up-section into the Tertiary metamorphic sequence, without supporting structural data. Some workers recognize a Main Central Thrust zone of high ductile strain up to 2-3 km thick, bounded by an upper thrust, MCT-2 (¼ Vaikrita thrust), and a lower thrust, MCT-1 (¼ Munsiari thrust). Some workers define an 'upper Lesser Himalaya' thrust sheet that shows similar P-T conditions to the Greater Himalayan Sequence. Others define the Main Central Thrust either on isotopic (Nd, Sr) differences, differences in detrital zircon ages, or as being coincident with a zone of young (,5 Ma) Th-Pb monazite ages. Very few papers incorporate any structural data in justifying the position of the Main Central Thrust. These studies, combined with recent quantitative strain analyses from the Everest and Annapurna Greater Himalayan Sequence, show that a wide region of high strain characterizes most of the Greater Himalayan Sequence with a concentration along the bounding margins of the South Tibetan Detachment along the top, and the Main Central Thrust along the base. We suggest that the Main Central Thrust has to be defined and mapped on strain criteria, not on stratigraphic, lithological, isotopic or geochronological criteria. The most logical place to map the Main Central Thrust is along the high-strain zone that commonly occurs along the base of the ductile shear zone and inverted metamorphic sequence. Above that horizon, all rocks show some degree of Tertiary Himalayan metamorphism, and most of the Greater Himalayan Sequence metamorphic or migmatitic rocks show some degree of pure shear and simple shear ductile strain that occurs throughout the mid-crustal Greater Himalayan Sequence channel. The Main Central Thrust evolved both in time (earlymiddle Miocene) and space from a deep-level ductile shear zone to a shallow brittle thrust fault.

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Conservation and redistribution of crust during the Indo-Asian collision

Yakovlev

Clark

2014

Tectonics

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We evaluate the mass balance of the Indo-Asian orogen by reconstructing the Indian and Asian margins prior to collision using recently published paleomagnetic and surface shortening constraints, and subtracting modern crustal volumes derived from gravity inversions and deep seismic soundings. Results show a~30% deficit between original and modern orogen volumes if the average global crustal thickness of 41 km is assumed prior to collision, even once eastward extrusion and crustal flow are considered. Such a large discrepancy requires crustal recycling of a magnitude that is greater than one half of the modern orogenic mass, as others have previously suggested. Proposals for extensive high elevations prior to or soon after the collision further exacerbate this mismatch and dramatically increase the volume of material necessary to be placed into the mantle. However, we show that this discrepancy can be eliminated with a 23-29 km thick crust within the orogen prior to collision along with a thick southern Tibet margin (the Lhasa and Qiangtang terranes). Because of the relatively low magnitude of surface shortening in Asia, an initially thin crust would require underplating of Indian crust in southern Tibet and displacement of a highly mobile lower crust to the north and east in order to explain modern crustal thicknesses. The contrast between a proposed thinner Asian interior and older and thicker lithosphere of the North China block may have defined the distal extent of deformation at the time of collision and since.

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Tectonic evolution of the Himalayan thrust belt in western Nepal: Implications for channel flow models

Cited by 75 publications

References 0 publications

Along-strike changes in Himalayan thrust geometry: Topographic and tectonic discontinuities in western Nepal

Along-strike changes in Himalayan thrust geometry: Topographic and tectonic discontinuities in western Nepal

Defining the Himalayan Main Central Thrust in Nepal

Conservation and redistribution of crust during the Indo-Asian collision

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