Journal articles: 'Himalayan Thrust'

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Mandal, Subhadip, Delores M. Robinson, Matthew J. Kohn, Subodha Khanal, and Oindrila Das. "Examining the tectono-stratigraphic architecture, structural geometry, and kinematic evolution of the Himalayan fold-thrust belt, Kumaun, northwest India." Lithosphere 11, no. 4 (2019): 414–35. http://dx.doi.org/10.1130/l1050.1.

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Abstract Existing structural models of the Himalayan fold-thrust belt in Kumaun, northwest India, are based on a tectono-stratigraphy that assigns different stratigraphy to the Ramgarh, Berinag, Askot, and Munsiari thrusts and treats the thrusts as separate structures. We reassess the tectono-stratigraphy of Kumaun, based on new and existing U-Pb zircon ages and whole-rock Nd isotopic values, and present a new structural model and deformation history through kinematic analysis using a balanced cross section. This study reveals that the rocks that currently crop out as the Ramgarh, Berinag, Askot, and Munsiari thrust sheets were part of the same, once laterally continuous stratigraphic unit, consisting of Lesser Himalayan Paleoproterozoic granitoids (ca. 1850 Ma) and metasedimentary rocks. These Paleoproterozoic rocks were shortened and duplexed into the Ramgarh-Munsiari thrust sheet and other Paleoproterozoic thrust sheets during Himalayan orogenesis. Our structural model contains a hinterland-dipping duplex that accommodates ∼541–575 km or 79%–80% of minimum shortening between the Main Frontal thrust and South Tibetan Detachment system. By adding in minimum shortening from the Tethyan Himalaya, we estimate a total minimum shortening of ∼674–751 km in the Himalayan fold-thrust belt. The Ramgarh-Munsiari thrust sheet and the Lesser Himalayan duplex are breached by erosion, separating the Paleoproterozoic Lesser Himalayan rocks of the Ramgarh-Munsiari thrust into the isolated, synclinal Almora, Askot, and Chiplakot klippen, where folding of the Ramgarh-Munsiari thrust sheet by the Lesser Himalayan duplex controls preservation of these klippen. The Ramgarh-Munsiari thrust carries the Paleoproterozoic Lesser Himalayan rocks ∼120 km southward from the footwall of the Main Central thrust and exposed them in the hanging wall of the Main Boundary thrust. Our kinematic model demonstrates that propagation of the thrust belt occurred from north to south with minor out-of-sequence thrusting and is consistent with a critical taper model for growth of the Himalayan thrust belt, following emplacement of midcrustal Greater Himalayan rocks. Our revised stratigraphy-based balanced cross section contains ∼120–200 km greater shortening than previously estimated through the Greater, Lesser, and Subhimalayan rocks.

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Thakur, V. C., R. Jayangondaperumal, and V. Joevivek. "Seismotectonics of central and NW Himalaya: plate boundary–wedge thrust earthquakes in thin- and thick-skinned tectonic framework." Geological Society, London, Special Publications 481, no. 1 (2018): 41–63. http://dx.doi.org/10.1144/sp481.8.

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AbstractThe tectonic framework of NW Himalaya is different from that of the central Himalaya with respect to the position of the Main Central Thrust and Higher Himalayan Crystalline and the Lesser and Sub Himalayan structures. The former is characterized by thick-skinned tectonics, whereas the thin-skinned model explains the tectonic evolution of the central Himalaya. The boundary between the two segments of Himalaya is recognized along the Ropar–Manali lineament fault zone. The normal convergence rate within the Himalaya decreases from c. 18 mm a−1 in the central to c. 15 mm a−1 in the NW segments. In the last 800 years of historical accounts of large earthquakes of magnitude Mw ≥ 7, there are seven earthquakes clustered in the central Himalaya, whereas three reported earthquakes are widely separated in the NW Himalaya. The earthquakes in central Himalaya are inferred as occurring over the plate boundary fault, the Main Himalayan Thrust. The wedge thrust earthquakes in NW Himalaya originate over the faults on the hanging wall of the Main Himalayan Thrust. Palaeoseismic evidence recorded on the Himalayan front suggests the occurrence of giant earthquakes in the central Himalaya. The lack of such an event reported in the NW Himalaya may be due to oblique convergence.

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Kafle, Nirmal, Lelin Raj Dhungel, Kamala Kanta Acharya, and Megh Raj Dhital. "A Balanced Geological Cross-Section along Kohalpur – Surkhet Area of Sub-Himalayan Range, Mid-Western Nepal." Journal of Science and Engineering 6 (May 3, 2019): 1–8. http://dx.doi.org/10.3126/jsce.v6i0.23960.

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The Sub-Himalayans Zone comprises a tectonic wedge of syn-orogenic sediments along the outer Himalayan Belt. Sediments are integrated into the accretionary prism from the foreland Indo-Gangetic plain, undergo a tectonic cycle within it, and eventually are eroded. The structural sketch map unveils westward-plunging arcuate structures on the leading location of the Outer Belt. A balanced cross-section has been constructed across the Sub-Himalayan Hills of the Kohalpur-Surkhet region of mid-western Nepal in order to determine the structural geometry of the region and to calculate tectonic shortening. The mid-western Nepal Sub-Himalaya has an emergent splay fan geometry with no major prevailing thrust contains the Main Boundary Thrust (MBT), the Bheri Thrust, the Babai Thrust and the Main frontal Thrust (MFT) which are all imbricate of the main decollment which ramp up-section through the 5 km thick tectonic sedimentary prism. North-south shortening across the mid-western Nepal, Kohalpur-Surkhet section has been approximately 29 km, or 55% shortening.

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Duvall, Michael J., John W. F. Waldron, Laurent Godin, and Yani Najman. "Active strike-slip faults and an outer frontal thrust in the Himalayan foreland basin." Proceedings of the National Academy of Sciences 117, no. 30 (2020): 17615–21. http://dx.doi.org/10.1073/pnas.2001979117.

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The Himalayan foreland basin formed by flexure of the Indian Plate below the advancing orogen. Motion on major thrusts within the orogen has resulted in damaging historical seismicity, whereas south of the Main Frontal Thrust (MFT), the foreland basin is typically portrayed as undeformed. Using two-dimensional seismic reflection data from eastern Nepal, we present evidence of recent deformation propagating >37 km south of the MFT. A system of tear faults at a high angle to the orogen is spatially localized above the Munger-Saharsa basement ridge. A blind thrust fault is interpreted in the subsurface, above the sub-Cenozoic unconformity, bounded by two tear faults. Deformation zones beneath the Bhadrapur topographic high record an incipient tectonic wedge or triangle zone. The faults record the subsurface propagation of the Main Himalayan Thrust (MHT) into the foreland basin as an outer frontal thrust, and provide a modern snapshot of the development of tectonic wedges and lateral discontinuities preserved in higher thrust sheets of the Himalaya, and in ancient orogens elsewhere. We estimate a cumulative slip of ∼100 m, accumulated in <0.5 Ma, over a minimum slipped area of ∼780 km2. These observations demonstrate that Himalayan ruptures may pass under the present-day trace of the MFT as blind faults inaccessible to trenching, and that paleoseismic studies may underestimate Holocene convergence.

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Paudel, Lalu Prasad. "Thin-Skinned Tectonics of the Tansen-Pokhara Section, Central Nepal Himalaya." Journal of Natural History Museum 26 (December 17, 2015): 15–28. http://dx.doi.org/10.3126/jnhm.v26i0.14129.

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Geological field survey and structural analysis were carried out in the Tansen-Pokhara section of central Nepal in an attempt to unravel the thin-skinned tectonic geometry of the Lesser Himalaya. The Lesser Himalaya in the area forms a foreland-propagating duplex structure, each tectonic unit being a horse bounded by imbricate faults. The Upper Main Central Thrust and the Main Boundary Thrust are the roof and floor thrusts, respectively. The Bari Gad-Kali Gandaki Fault is an out-of-sequence fault. The Pindi Khola Fault is an antithetic back-thrust developed on the hangingwall of the Bari Gad-Kali Gandaki Fault, and the Kusma Fault is a splay-off of the Phalebas Thrust. Deformation of the Lesser Himalaya occurred in distinct three phases namely pre-Himalayan, Eohimalayan and Neohimalayan. The duplex structure was formed in the Neohimlayan stage in the period between Middle Miocene and Early Pleistocene. J. Nat. Hist. Mus. Vol. 26, 2012: 15-28

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Rai, L. K., K. K. Acharya, and M. R. Dhital. "Lithostratigraphy and structure of the Dharan–Mulghat area, Lesser Himalayan sequence, eastern Nepal Himalaya." Journal of Nepal Geological Society 51 (December 31, 2016): 77–78. http://dx.doi.org/10.3126/jngs.v51i0.24095.

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The Dharan–Mulghat area of the eastern Nepal can be divided into three tectonic units: the Higher Himalayan Crystallines, the Lesser Himalayan Sequence and the Siwaliks from north to south separated by the Main Central Thrust (MCT) and Main Boundary Thrust (MBT), respectively. The Lesser Himalayan Sequence is divided into two groups separated by Chimra Thrust: the Bhedetar Group and the Dada Bajar Group. The Bhedetar Group includes the Raguwa Formation, the Phalametar Quartzite, the Churibas Formation, the Sangure Quartzite, and the Karkichhap Formation from the bottom to top, respectively; overthrusted by the Dada Bajar Group consisting: the Ukhudanda Formation, the Mulghat Formation, the Okhre Formation, and the Patigau Formation, from lower to upper sections, respectively along the Chimra Thrust and the Bhorleni Formation as an individual formation overthrusted by Bhedetar Group along the Chhotimorang Thrust. The Main Central Thrust, the Main Boundary Thrust, the Chimra Thrust and the Chhotimorang Thrust are the major faults in Dharan–Mulghat area. The Leutiphedi Anticline and the Malbase Syncline are the major folds in the study area plunging towards east. The trend/plunge of anticline and syncline are 131o/24o and 096o/09o respectively. The microstructural study in the quartz grains reveals a sharp difference in the history across the MCT; dynamic in the rocks of the Lesser Himalayan Sequences and static in the rocks of the Higher Himalayan Crystallines.

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Godin, Laurent, Renaud Soucy La Roche, Lindsay Waffle, and Lyal B. Harris. "Influence of inherited Indian basement faults on the evolution of the Himalayan Orogen." Geological Society, London, Special Publications 481, no. 1 (2018): 251–76. http://dx.doi.org/10.1144/sp481.4.

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AbstractIndian basement faults, which bound three orogen-perpendicular palaeotopographic ridges of Precambrian Indian basement south of the Himalaya, extend to the base of the Indian lithosphere and to the northern extent of the Indian lithosphere underneath Tibet. In the eastern Himalaya, the active orogen-perpendicular Yadong–Gulu graben is aligned with an earthquake-generating strike-slip fault in the high Himalaya. We argue that the graben results from crustal necking during reactivation of the underplated basement fault. In the central Himalaya, along-strike diachronous deformation and metamorphism within the Himalayan metamorphic core, as well as lateral ramps in the foreland thrust belt, spatially correspond to the Lucknow and Pokhara lineaments that bound the subsurface Faizabad Ridge in the Indian basement. Analogue centrifuge modelling confirms that offset along such deep-seated basement faults can affect the location, orientation and type of structures developed at various stages of orogenesis and suggests that it is mechanically feasible for strain to propagate through a melt-weakened mid-crust. We suggest that inherited Indian basement faults affect the ramp-flat geometry of the basal Main Himalayan Thrust, partition the Himalayan range into distinct zones, localize east–west extension resulting in the Tibetan graben and, ultimately, contribute to lateral variability in tectonic evolution along the orogen's strike.

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Ojha, Lujendra, Ken L. Ferrier, and Tank Ojha. "Millennial-scale denudation rates in the Himalaya of Far Western Nepal." Earth Surface Dynamics 7, no. 4 (2019): 969–87. http://dx.doi.org/10.5194/esurf-7-969-2019.

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Abstract. The Himalayas stretch ∼3000 km along the Indo-Eurasian plate boundary. Along-strike variations in the fault geometry of the Main Himalayan Thrust (MHT) have given rise to significant variations in the topographic steepness, exhumation rate, and orographic precipitation along the Himalayan front. Over the past 2 decades, the rates and patterns of Himalayan denudation have been documented through numerous cosmogenic nuclide measurements in central and eastern Nepal, Bhutan, and northern India. To date, however, few denudation rates have been measured in Far Western Nepal, a ∼300 km wide region near the center of the Himalayan arc, which presents a significant gap in our understanding of Himalayan denudation. Here we report new catchment-averaged millennial-scale denudation rates inferred from cosmogenic 10Be in fluvial quartz at seven sites in Far Western Nepal. The inferred denudation rates range from 385±31 t km−2 yr−1 (0.15±0.01 mm yr−1) to 8737±2908 t km−2 yr−1 (3.3±1.1 mm yr−1) and, in combination with our analyses of channel topography, are broadly consistent with previously published relationships between catchment-averaged denudation rates and normalized channel steepness across the Himalaya. These data show that the denudation rate patterns in Far Western Nepal are consistent with those observed in central and eastern Nepal. The denudation rate estimates from Far Western Nepal show a weak correlation with catchment-averaged specific stream power, consistent with a Himalaya-wide compilation of previously published stream power values. Together, these observations are consistent with a dependence of denudation rate on both tectonic and climatic forcings, and they represent a first step toward filling an important gap in denudation rate measurements in Far Western Nepal.

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Kanaujia, Jyotima, Supriyo Mitra, S. C. Gupta, and M. L. Sharma. "Crustal anisotropy from shear-wave splitting of local earthquakes in the Garhwal Lesser Himalaya." Geophysical Journal International 219, no. 3 (2019): 2013–33. http://dx.doi.org/10.1093/gji/ggz404.

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SUMMARY Crustal anisotropy of the Garhwal Lesser Himalaya has been studied using local earthquake data from the Tehri seismic network. Earthquakes with magnitude (mL) up to 3, which occurred between January 2008 to December 2010, have been used for the shear wave splitting (SWS) analysis. SWS measurements have been done for steeply incident ray paths (ic ≤ 45°) to estimate the anisotropy fast axis orientation (ϕ) and the delay time (∂t). A total of 241 waveforms have been analysed, which yielded 209 splitting measurements, and 32 null results. The analysis reveals spatial and depth variation of ϕ and ∂t, suggesting complex anisotropic structure beneath the Garhwal Lesser Himalaya. The mean ∂t is estimated to be 0.07 ± 0.065 s with a mean depth normalized ∂t of 0.005 s km–1. We present the ϕ and Vs per cent anisotropy results by segregating these as a function of depth, for earthquakes originating above and below the Main Himalayan Thrust (MHT); and spatially, for stations located in the Outer Lesser Himalaya (OLH) and the Inner Lesser Himalaya (ILH). Earthquakes above the MHT sample only the Himalayan wedge, while those below the MHT sample both the underthrust Indian crust and the Himalayan wedge. Within the Himalayan wedge, for both OLH and ILH, the mean ϕ is oriented NE–SW, in the direction of maximum horizontal compressive stress axis (SHmax). This anisotropy is possibly due to stress-aligned microcracks controlled by the local stress pattern within the Himalayan wedge. The mean of normalized ∂t for all events originating within the Himalaya is 0.006 s km–1, which yields a Vs per cent anisotropy of ∼2.28 per cent. Assuming a homogeneous distribution of stress-aligned microcracks we compute a crack density of ∼0.0228 for the Garhwal Lesser Himalaya. At stations close to the regional fault systems, the mean ϕ is subparallel to the strike of the faults, and the anisotropy, locally, appears to be structure-related. For earthquakes originating below the MHT, in OLH, the mean ϕ orientation matches those from the Himalayan wedge and the normalized ∂t decreases with depth. This suggests depth localization of the anisotropy, primarily present within the Himalayan wedge. In the ILH, we observe large variations in the mean ϕ orientation and larger values of ∂t close to the regional fault/thrust systems. This is possibly a composite effect of the structure-related shallow crustal anisotropy and the frozen anisotropy of the underthrusting Indian crust. However, these cannot be segregated in this study.

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Priestley, Keith, Tak Ho, and Supriyo Mitra. "The crustal structure of the Himalaya: A synthesis." Geological Society, London, Special Publications 483, no. 1 (2019): 483–516. http://dx.doi.org/10.1144/sp483-2018-127.

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AbstractThis chapter examines the along-arc variation in the crustal structure of the Himalayan Mountain Range. Using results from published seismological studies, plus large teleseismic body-wave and surface-wave datasets which we analyse, we illustrate the along-arc variation by comparing the crustal properties beneath four representative areas of the Himalayan Mountain Range: the Western Syntaxis, the Garhwal–Kumaon, the Eastern Nepal–Sikkim, and the Bhutan–Northeastern India regions. The Western Syntaxis and the Bhutan–Northeastern India regions have a complicated structure extending far out in front of the main Range, whereas the Central Himalaya appear to have a much simpler structure. The deformation is more distributed beneath the western and eastern ends of the Range, but in general, the crust gradually thickens from c. 40 km on the southern side of the Foreland Basin to c. 80 km beneath the Tethys Himalaya. While the gross crustal structure of much of the Himalaya is becoming better known, our understanding of the internal structure of the Himalaya is still sketchy. The detailed geometry of the Main Himalayan Thrust and the role of the secondary structures on the underthrusting Indian Plate are yet to be characterized satisfactorily.

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Jouanne, François, Jean Louis Mugnier, Som Nath Sapkota, Pascale Bascou, and Arnaud Pecher. "Estimation of coupling along the Main Himalayan Thrust in the central Himalaya." Journal of Asian Earth Sciences 133 (January 2017): 62–71. http://dx.doi.org/10.1016/j.jseaes.2016.05.028.

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Pognante, U., D. Castelli, P. Benna, et al. "The crystalline units of the High Himalayas in the Lahul–Zanskar region (northwest India): metamorphic–tectonic history and geochronology of the collided and imbricated Indian plate." Geological Magazine 127, no. 2 (1990): 101–16. http://dx.doi.org/10.1017/s0016756800013807.

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AbstractIn the High Himalayan belt of northwest India, crustal thickening linked to Palaeogene collision between India and Eurasia has led to the formation of two main crystalline tectonic units separated by the syn-metamorphic Miyar Thrust: the High Himalayan Crystallines sensu stricto (HHC) at the bottom, and the Kade Unit at the top. These units are structurally interposed between the underlying Lesser Himalaya and the very low-grade sediments of the Tibetan nappes. They consist of paragneisses, orthogneisses, minor metabasics and, chiefly in the HHC, leucogranites. The HHC registers: a polyphase metamorphism with two main stages designated as M1 and M2; a metamorphic zonation with high-temperature recrystallization and migmatization at middle structural levels and medium-temperature assemblages at upper and lower levels. In contrast, the Kade Unit underwent a low-temperature metamorphism. Rb–Sr and U–Th–Pb isotope data point to derivation of the orthogneisses from early Palaeozoic granitoids, while the leucogranites formed by anatexis of the HHC rocks and were probably emplaced during Miocene time.Most of the complicated metamorphic setting is related to polyphase tectonic stacking of the HHC with the ‘cooler’ Kade Unit and Lesser Himalaya during the Himalayan history. However, a few inconsistencies exist for a purely Himalayan age of some Ml assemblages of the HHC. As regards the crustal-derived leucogranites, the formation of a first generation mixed with quartzo-feldspathic leucosomes was possibly linked to melt-lubricated shear zones which favoured rapid crustal displacements; at upper levels they intruded during stage M2 and the latest movements along the syn-metamorphic Miyar Thrust, but before juxtaposition of the Tibetan nappes along the late- metamorphic Zanskar Fault.

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Brunel, Maurice, and Jean-Robert Kienast. "Étude pétro-structurale des chevauchements ductiles himalayens sur la transversale de l'Everest–Makalu (Népal oriental)." Canadian Journal of Earth Sciences 23, no. 8 (1986): 1117–37. http://dx.doi.org/10.1139/e86-111.

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Tectonic and microtectonic data in eastern Nepal indicate that the major observed thrusting (100 km) on the Main Central Thrust (MCT) postdates the Barrovian metamorphism of the High Himalaya gneisses. This result, at variance with the famous "reverse metamorphism model," better explains the abnormal metamorphic superpositions in the Himalayas and accounts for the lack of high-pressure assemblages under the thick, allochtonous High Himalaya Tibetan slab.Pressure and temperature estimates by microprobe analysis on plagioclase, biotite, garnet, kyanite, sillimanite, and cordierite assemblages are presented for samples collected along the MCT shear zone and across the gneiss slab in the Everest–Makalu area. Since there is very little difference in pressure at the front of the slab (Kathmandu Klippe) and its root, these estimates support the existence of important late metamorphic thrusting. The decrease of pressure towards the top of the gneiss pile, combined with a small temperature increase, explains the kyanite–sillimanite transition. The reverse metamorphism model, which implies refolded isograds, predicts heat loss by conduction throughout the sole of the thrust; pressure–temperature variations and kyanite–sillimanite transition phases more likely reflect a late heat supply in the upper part of the gneisses. Intrusion of leucogranitic bodies, confined to the interface with the Tethyan sediments, could account for this heat supply.A new tectonic evolution model of the Himalayan intracrustal thrusts is discussed. Without completely denying the existence of a reverse metamorphism synchronous with the phases of early shearing, it can be shown that the metamorphic zonation seen at present was governed by the structure of the later shearing.

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Bilham, Roger. "Himalayan earthquakes: a review of historical seismicity and early 21st century slip potential." Geological Society, London, Special Publications 483, no. 1 (2019): 423–82. http://dx.doi.org/10.1144/sp483.16.

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AbstractThis article summarizes recent advances in our knowledge of the past 1000 years of earthquakes in the Himalaya using geodetic, historical and seismological data, and identifies segments of the Himalaya that remain unruptured. The width of the Main Himalayan Thrust is quantified along the arc, together with estimates for the bounding coordinates of historical rupture zones, convergence rates, rupture propagation directions as constrained by felt intensities. The 2018 slip potential for fifteen segments of the Himalaya are evaluated and potential magnitudes assessed for future earthquakes should these segments fail in isolation or as contiguous ruptures. Ten of these fifteen segments are sufficiently mature currently to host a great earthquake (Mw ≥ 8). Fatal Himalayan earthquakes have in the past occurred mostly in the daylight hours. The death toll from a future nocturnal earthquake in the Himalaya could possibly exceed 100 000 due to increased populations and the vulnerability of present-day construction methods.

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Stevens, V. L., and J. P. Avouac. "Interseismic coupling on the main Himalayan thrust." Geophysical Research Letters 42, no. 14 (2015): 5828–37. http://dx.doi.org/10.1002/2015gl064845.

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Acharya, Ravi, Saurav Khanal, Surya Prasad Kandel, et al. "Balanced cross-section across the Siwaliks of the Trijuga Valley, eastern Nepal." Journal of Nepal Geological Society 60 (September 16, 2020): 51–58. http://dx.doi.org/10.3126/jngs.v60i0.31263.

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The strata of the Siwalik Group in the Trijuga valley is dissected by two thrusts, repeating the succession three times and forming a longitudinal Dun Valley. The total thickness of the Siwalik strata exceeds 5000 m in the area. A balanced cross-section has been constructed across the Siwalik Range in the Trijuga valley showing that the Main Himalayan Thrust (MHT) lies at the depth of about 5.2 km from the surface. The Main Frontal Thrust (MFT), Kamala Tawa Thrust (KTT), Marine Khola Thrust (MKT) and Main Boundary Thrust (MBT) ramp-up from the MHT. Along with these faults, fault-bend anticlines associated with these thrusts have shortened the Siwalik of the area. The shortening across the area has been calculated to be approximately 33.7 km.

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Tamang, Shashi, Sandeep Thapa, Kabi Raj Paudyal, Frédéric Girault, and Frédéric Perrier. "Geology and mineral resources of Khudi-Bahundanda area of west-central Nepal along Marshyangdi Valley." Journal of Nepal Geological Society 58 (June 25, 2019): 97–103. http://dx.doi.org/10.3126/jngs.v58i0.24592.

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Geological study was carried out along the Khudi-Bahundanda area of the Marshyangdi Valley in the west central Nepal. The area lies partly in the Main Central Thrust (MCT) zone and partly in the Higher Himalayan Crystalline Zone. The aim of the study was to prepare a detail geological map and cross section in the scale of 1:25,000 to work out on stratigraphy, metamorphism and mineral resource potential of the area. The rocks of the Higher Himalaya have been mapped under a single unit as Formation I. This unit consists of kyanite-garnet para-gneiss. The lithological units of the MCT zone are mapped into three units as the Benighat Slate, the Malekhu Formation and the Robang Formation from the bottom to the top, respectively. The Benighat Slate consists of dark grey to black schist with some carbonate beds as members. The Malekhu Formation consists of creamy white siliceous dolomite marble with parting of schist. The Robang Formation comprises of light grey psammitic schist with garnet and white micaceous quartzite in various proportion. Many secondary structures are observed in the study area, but primary structures are missing due to extreme metamorphism. The large-scale structures are the MCT, which separates the Lesser Himalayan rocks to the south from the Higher Himalaya to the north, and the Bahundanda Thrust (BT). Numerous outcrop-scale structures like meso-scale folds, quartz veins, boudinage and ptygmatic folds are abundant. Folds in the MCT zone are mostly E-W trending, and rocks have experienced multiple metamorphism and dynamic crystallization of minerals. The Lesser Himalayan rocks resemble the garnet zone while the Higher Himalayan rocks resemble to the kyanite grade of metamorphism. As in the other sections of the Himalaya, the present section also clearly shows the inverted metamorphism in the MCT zone. The MCT zone is considered as the potential site for precious and semi-precious stones, of which the most potential ones are the garnet and kyanite.

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Oliver, G. J. H., M. R. W. Johnson, and A. E. Fallick. "Age of metamorphism in the Lesser Himalaya and the Main Central Thrust zone, Garhwal India: results of illite crystallinity,40Ar–39Ar fusion and K–Ar studies." Geological Magazine 132, no. 2 (1995): 139–49. http://dx.doi.org/10.1017/s0016756800011717.

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AbstractIllite crystallinity data from the Lesser Himalaya of Garhwal show that the upper Paleocene-lower Eocene Subathu Formation, deposited immediately prior to or early in the Himalayan collision, has not suffered significant regional metamorphism. The regional metamorphism in the upper Precambrian–lower Palaeozoic Lesser Himalaya must therefore be precollisional. Illite crystallinity results from Lesser Himalayan fossiliferous Permian strata show grades of metamorphism intermediate between upper Paleocene–lower Eocene and Proterozoic–lower Palaeozoic strata indicating a pre-Permian regional metamorphism for the latter.K–Ar whole rock cooling ages provide supporting evidence for pre-collisional regional metamorphism in the Lesser Himalaya. Slates and phyllites below the Main Central Thrust (MCT) show pre-Cenozoic whole rock ages, as old as Ordovician (486 Ma). Whilst resetting of K–Ar whole rock ages has occurred locally in pervasively cleaved Palaeozoic strata (near thrusts?), fracture cleaved Permian and upper Paleocene–lower Eocene sediments give whole rock ages compatible with diagenesis. The illite crystallinity results confirm that these sediments have not been heated above mica blocking temperatures.Muscovite40Ar–39Ar and K–Ar mineral ages within the 5 km thick MCT zone are as young as 8 Ma indicating that temperatures of above ~ 350°C were maintained in the MCT zone for over 10 Ma after high temperature (~ 550°C) shearing on the MCT. This heating did not affect the MCT footwall Lesser Himalaya to any regional extent, where pre-Permian low grade regional metamorphism has not been overprinted.

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Hopkinson, Thomas, Nigel Harris, Nick M. W. Roberts, et al. "Evolution of the melt source during protracted crustal anatexis: An example from the Bhutan Himalaya." Geology 48, no. 1 (2019): 87–91. http://dx.doi.org/10.1130/g47078.1.

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Abstract The chemical compositions of magmatic zircon growth zones provide powerful insight into evolving magma compositions due to their ability to record both time and the local chemical environment. In situ U-Pb and Hf isotope analyses of zircon rims from Oligocene–Miocene leucogranites of the Bhutan Himalaya reveal, for the first time, an evolution in melt composition between 32 and 12 Ma. The data indicate a uniform melt source from 32 Ma to 17 Ma, and the progressive addition of an older source component to the melt from at least ca. 17 Ma. Age-corrected ɛHf ratios decrease from between −10 and −15 down to values as low as −23 by 12 Ma. Complementary whole-rock Nd isotope data corroborate the Hf data, with a progressive decrease in ɛNd(t) from ca. 18 to 12 Ma. Published zircon and whole-rock Nd data from different lithotectonic units in the Himalaya suggest a chemical distinction between the younger Greater Himalayan Series (GHS) and the older Lesser Himalayan Series (LHS). The time-dependent isotopic evolution shown in the leucogranites demonstrates a progressive increase in melt contribution from older lithologies, suggestive of increasing LHS involvement in Himalayan melting over time. The time-resolved data are consistent with LHS material being progressively accreted to the base of the GHS from ca. 17 Ma, facilitated by deformation along the Main Central thrust. From 17 Ma, decompression, which had triggered anatexis in the GHS since the Paleogene, enabled melting in older sources from the accreted LHS, now forming the lowermost hanging wall of the thrust.

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Godin, Laurent, Mark Ahenda, Djordje Grujic, Ross Stevenson, and John Cottle. "Protolith affiliation and tectonometamorphic evolution of the Gurla Mandhata core complex, NW Nepal Himalaya." Geosphere 17, no. 2 (2021): 626–46. http://dx.doi.org/10.1130/ges02326.1.

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Abstract Assigning correct protolith to high metamorphic-grade core zone rocks of large hot orogens is a particularly important challenge to overcome when attempting to constrain the early stages of orogenic evolution and paleogeography of lithotectonic units from these orogens. The Gurla Mandhata core complex in NW Nepal exposes the Himalayan metamorphic core (HMC), a sequence of high metamorphic-grade gneiss, migmatite, and granite, in the hinterland of the Himalayan orogen. Sm-Nd isotopic analyses indicate that the HMC comprises Greater Himalayan sequence (GHS) and Lesser Himalayan sequence (LHS) rocks. Conventional interpretation of such provenance data would require the Main Central thrust (MCT) to be also outcropping within the core complex. However, new in situ U-Th/Pb monazite petrochronology coupled with petrographic, structural, and microstructural observations reveal that the core complex is composed solely of rocks in the hanging wall of the MCT. Rocks from the core complex record Eocene and late Oligocene to early Miocene monazite (re-)crystallization periods (monazite age peaks of 40 Ma, 25–19 Ma, and 19–16 Ma) overprinting pre-Himalayan Ordovician Bhimphedian metamorphism and magmatism (ca. 470 Ma). The combination of Sm-Nd isotopic analysis and U-Th/Pb monazite petrochronology demonstrates that both GHS and LHS protolith rocks were captured in the hanging wall of the MCT and experienced Cenozoic Himalayan metamorphism during south-directed extrusion. Monazite ages do not record metamorphism coeval with late Miocene extensional core complex exhumation, suggesting that peak metamorphism and generation of anatectic melt in the core complex had ceased prior to the onset of orogen-parallel hinterland extension at ca. 15–13 Ma. The geometry of the Gurla Mandhata core complex requires significant hinterland crustal thickening prior to 16 Ma, which is attributed to ductile HMC thickening and footwall accretion of LHS protolith associated with a Main Himalayan thrust ramp below the core complex. We demonstrate that isotopic signatures such as Sm-Nd should be used to characterize rock units and structures across the Himalaya only in conjunction with supporting petrochronological and structural data.

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Puniya, M. K., R. C. Patel, and P. D. Pant. "Structural and thermochronological studies of the Almora klippe, Kumaun, NW India: implications for crustal thickening and exhumation of the NW Himalaya." Geological Society, London, Special Publications 481, no. 1 (2018): 81–110. http://dx.doi.org/10.1144/sp481-2017-74.

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AbstractCrystalline klippen over the Lesser Himalayan Metasedimentary Sequence (LHMS) zone in the NW Himalaya have specific syn- and post-emplacement histories. These tectonics also provide a means to understand the driving factors responsible for the exhumation of the rocks of crystalline klippen during the Himalayan Orogeny. New meso- and microscale structural analyses, and thermochronological studies across the LHMS zone, Ramgarh Thrust (RT) sheet and Almora klippe in the eastern Kumaun region, NW Himalaya, indicate that the RT sheet and Almora klippe were a part of the Higher Himalayan Crystalline (HHC) of the Indian Plate which underwent at least one episode of pre-Himalayan deformation and polyepisodic Himalayan deformation in ductile and brittle–ductile regimes. The deformation temperature pattern within the Almora klippe records a normal thermal profile from its base to top but an inverted thermal profile from the base of Almora klippe down towards the LHMS zone. New fission-track data collected across the RT sheet and Almora klippe along Chalthi–Champawat–Pithoragarh traverse in the east Kumaun region document the exhumation of both units since Eocene times. Zircon fission-track (ZFT) ages from the Almora klippe range between 28.7 ± 2.4 and 17.6 ± 1.1 Ma, and from the RT sheet between 29.8 ± 1.6 and 22.6 ± 1.9 Ma; and the apatite fission-track (AFT) ages from the Almora klippe range between 15.1 ± 1.7 and 3.4 ± 0.5 Ma, and from the RT sheet between 8.7 ± 1.2 and 4.6 ± 0.6 Ma. The age pattern and diverse patterns of the exhumation rates reflect a clear tectonic signal in the RT sheet and the Almora klippe which acknowledge that the Cenozoic tectonics influenced the exhumation pattern in the Himalaya.

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22

VANNAY, JEAN-CLAUDE, and BERNHARD GRASEMANN. "Himalayan inverted metamorphism and syn-convergence extension as a consequence of a general shear extrusion." Geological Magazine 138, no. 3 (2001): 253–76. http://dx.doi.org/10.1017/s0016756801005313.

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Two paradoxical geological features of the Himalaya are the syn-convergence extension and the inverted metamorphic isograds observed in the crystalline core zone of this orogen. This High Himalayan Crystalline Sequence corresponds to an up to 40 km thick sequence of amphibolite to granulite facies gneiss, bounded by the Main Central Thrust at the base, and by the extensional faults of the South Tibetan Detachment System at the top. Geochronological and structural data demonstrate that coeval movements along both the Main Central Thrust and South Tibetan Detachment System during Early to Middle Miocene times were related to a tectonically controlled exhumation of these high-grade metamorphic rocks. The High Himalayan Crystalline Sequence systematically shows an inverted metamorphic zonation, generally characterized by a gradual superposition of garnet, staurolite, kyanite, sillimanite + muscovite and sillimanite + K-feldspar isograds, from the base to the top of the unit. Recent kinematic flow analyses of these metamorphic rocks demonstrate the coexistence of both simple shear and pure shear during the ductile deformation. The simple shear component of such a general non-coaxial flow could explain a rotation of isograds, eventually resulting in an inversion. The pure shear component of the flow implies a thinning of the metamorphic sequence that must be balanced by a perpendicular stretching of the unit parallel to its boundaries. Inasmuch as seismic data show that both the Main Central Thrust and South Tibetan Detachment System converge at depth, a thinning of the wedge-shaped High Himalayan Crystalline Sequence should induce a ductile extrusion of these high-grade rocks toward the surface. Rapid extension at the top of the sequence could thus be the consequence of a general shear extrusion of this unit relative to its hanging wall. Moreover, this extensional movement should decrease with depth to become zero where the boundaries of the unit meet, accounting for the paradoxical convergence of the South Tibetan Detachment System toward the Main Central Thrust. Furthermore, a general flow combining simple shear and pure shear can reconcile inverted isograds with the lack of inverted pressure field gradient across the High Himalayan Crystalline Sequence, despite an intense non-coaxial deformation. In good agreement with the seismic, kinematic and P–T–t constraints on the Himalayan tectono-thermal evolution, general shear extrusion provides a consistent model accounting for both inverted isograds and rapid extension in a compressional orogenic setting.

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23

Bai, Ling, Simon L. Klemperer, James Mori, et al. "Lateral variation of the Main Himalayan Thrust controls the rupture length of the 2015 Gorkha earthquake in Nepal." Science Advances 5, no. 6 (2019): eaav0723. http://dx.doi.org/10.1126/sciadv.aav0723.

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The Himalaya orogenic belt produces frequent large earthquakes that affect population centers along a length of over 2500 km. The 2015 Gorkha, Nepal earthquake (Mw 7.8) ruptured the Main Himalayan Thrust (MHT) and allows direct measurements of the behavior of the continental collision zone. We study the MHT using seismic waveforms recorded by local stations that completely cover the aftershock zone. The MHT exhibits clear lateral variation along geologic strike, with the Lesser Himalayan ramp having moderate dip on the MHT beneath the mainshock area and a flatter and deeper MHT beneath the eastern end of the aftershock zone. East of the aftershock zone, seismic wave speed increases at MHT depths, perhaps due to subduction of an Indian basement ridge. A similar magnitude wave speed change occurs at the western end of the aftershock zone. These gross morphological structures of the MHT controlled the rupture length of the Gorkha earthquake.

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SEARLE, MICHAEL P., RICHARD D. LAW, LAURENT GODIN, et al. "Defining the Himalayan Main Central Thrust in Nepal." Journal of the Geological Society 165, no. 2 (2008): 523–34. http://dx.doi.org/10.1144/0016-76492007-081.

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25

Malik, Javed N., Ashutosh Kumar, Sravanthi Satuluri, Bishuddhakshya Puhan, and Asmita Mohanty. "Ground-Penetrating Radar Investigations along Hajipur Fault: Himalayan Frontal Thrust—Attempt to Identify Near Subsurface Displacement, NW Himalaya, India." International Journal of Geophysics 2012 (2012): 1–7. http://dx.doi.org/10.1155/2012/608269.

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The study area falls in the mesoseismal zone of 1905 Kangra earthquake (Mw 7.8). To identify appropriate trenching site for paleoseismic investigation and to understand the faulting geometry, ground-penetrating radar (GPR) survey was conducted across a Hajipur Fault (HF2) scarp, a branching out fault of Himalayan Frontal Thrust (HFT) in a foot hill zone of NW Himalaya. Several 2D and 3D profiles were collected using 200 MHz antenna with SIR 3000 unit. A 2D GPR profile collected across the HF2 scarp revealed prominent hyperbolas and discontinuous-warped reflections, suggesting a metal pipe and a zone of deformation along a low-angle thrust fault, respectively. The 3D profile revealed remarkable variation in dip of the fault plane and pattern of deformation along the strike of the fault.

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Larson, Kyle P., Tyler K. Ambrose, A. Alexander G. Webb, John M. Cottle, and Sudip Shrestha. "Reconciling Himalayan midcrustal discontinuities: The Main Central thrust system." Earth and Planetary Science Letters 429 (November 2015): 139–46. http://dx.doi.org/10.1016/j.epsl.2015.07.070.

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Khanal, S., D. M. Robinson, M. J. Kohn, and S. Mandal. "Evidence for a far-traveled thrust sheet in the Greater Himalayan thrust system, and an alternative model to building the Himalaya." Tectonics 34, no. 1 (2015): 31–52. http://dx.doi.org/10.1002/2014tc003616.

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28

Caldwell, Warren B., Simon L. Klemperer, Jesse F. Lawrence, Shyam S. Rai, and Ashish. "Characterizing the Main Himalayan Thrust in the Garhwal Himalaya, India with receiver function CCP stacking." Earth and Planetary Science Letters 367 (April 2013): 15–27. http://dx.doi.org/10.1016/j.epsl.2013.02.009.

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29

Chamlagain, D., and D. Hayashi. "Numerical simulation of fault development in fold-and-thrust belt of Nepal Himalaya." Himalayan Journal of Sciences 2, no. 4 (2008): 111. http://dx.doi.org/10.3126/hjs.v2i4.821.

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30

Dey, Saptarshi, Rasmus C. Thiede, Arindam Biswas, Naveen Chauhan, Pritha Chakravarti, and Vikrant Jain. "Implications of the ongoing rock uplift in NW Himalayan interiors." Earth Surface Dynamics 9, no. 3 (2021): 463–85. http://dx.doi.org/10.5194/esurf-9-463-2021.

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Abstract. The Lesser Himalaya exposed in the Kishtwar Window (KW) of the Kashmir Himalaya exhibits rapid rock uplift and exhumation (∼3 mm yr−1) at least since the late Miocene. However, it has remained unclear if it is still actively deforming. Here, we combine new field, morphometric and structural analyses with dating of geomorphic markers to discuss the spatial pattern of deformation across the window. We found two steep stream segments, one at the core and the other along the western margin of the KW, which strongly suggest ongoing differential uplift and may possibly be linked to either crustal ramps on the Main Himalayan Thrust (MHT) or active surface-breaking faults. High bedrock incision rates (>3 mm yr−1) on Holocene–Pleistocene timescales are deduced from dated strath terraces along the deeply incised Chenab River valley. In contrast, farther downstream on the hanging wall of the MCT, fluvial bedrock incision rates are lower (<0.8 mm yr−1) and are in the range of long-term exhumation rates. Bedrock incision rates largely correlate with previously published thermochronologic data. In summary, our study highlights a structural and tectonic control on landscape evolution over millennial timescales in the Himalaya.

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Kanna, Nagaraju, and Sandeep Gupta. "Crustal seismic structure beneath the Garhwal Himalaya using regional and teleseismic waveform modelling." Geophysical Journal International 222, no. 3 (2020): 2040–52. http://dx.doi.org/10.1093/gji/ggaa282.

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SUMMARY We investigate the crustal seismic structure of the Garhwal Himalayan region using regional and teleseismic earthquake waveforms, recorded over 19 closely spaced broad-band seismic stations along a linear profile that traverses from the Sub Himalayas to Higher Himalayas. The regional earthquake traveltime analysis provides uppermost mantle P- and S-wave velocities as 8.2 and 4.5 km s−1, respectively. The calculated receiver functions from the teleseismic P waveforms show apparent P-to-S conversions from the Moho as well as from intracrustal depths, at most of the seismic stations. These conversions also show significant azimuthal variations across the Himalayas, indicating complex crustal structure across the Garhwal Himalaya. We constrain the receiver function modelling using the calculated uppermost mantle (Pn and Sn) velocities. Common conversion point stacking image of P-to-S conversions as well as receiver function modelling results show a prominent intracrustal low shear velocity layer with a flat–ramp–flat geometry beneath the Main Central Thrust zone. This low velocity indicates the possible presence of partial melts/fluids in the intracrustal depths beneath the Garhwal Himalaya. We correlate the inferred intracrustal partial melts/fluids with the local seismicity and suggest that the intracrustal fluids are one of the possible reasons for the occurrence of upper-to-mid-crustal earthquakes in this area. The results further show that the Moho depth varies from ∼45 km beneath the Sub Himalayas to ∼58 km to the south of the Tethys Himalayas. The calculated lower crustal shear wave velocities of ∼3.9 and 4.3 km s−1 beneath the Lesser and Higher Himalayas suggest the presence of granulite and partially eclogite rocks in the lower crust below the Lesser and Higher Himalayas, respectively. We also suggest that the inferred lower crustal rocks are the possible reasons for the presence and absence of the lower crustal seismicity beneath the Lesser and Higher Himalayas, respectively.

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Searle, M. P., J. M. Cottle, M. J. Streule, and D. J. Waters. "Crustal melt granites and migmatites along the Himalaya: melt source, segregation, transport and granite emplacement mechanisms." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 100, no. 1-2 (2009): 219–33. http://dx.doi.org/10.1017/s175569100901617x.

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ABSTRACTIndia–Asia collision resulted in crustal thickening and shortening, metamorphism and partial melting along the 2200 km-long Himalayan range. In the core of the Greater Himalaya, widespread in situ partial melting in sillimanite+K-feldspar gneisses resulted in formation of migmatites and Ms+Bt+Grt+Tur±Crd±Sil leucogranites, mainly by muscovite dehydration melting. Melting occurred at shallow depths (4–6 kbar; 15–20 km depth) in the middle crust, but not in the lower crust. 87Sr/86Sr ratios of leucogranites are very high (0·74–0·79) and heterogeneous, indicating a 100 crustal protolith. Melts were sourced from fertile muscovite-bearing pelites and quartzo-feldspathic gneisses of the Neo-Proterozoic Haimanta–Cheka Formations. Melting was induced through a combination of thermal relaxation due to crustal thickening and from high internal heat production rates within the Proterozoic source rocks in the middle crust. Himalayan granites have highly radiogenic Pb isotopes and extremely high uranium concentrations. Little or no heat was derived either from the mantle or from shear heating along thrust faults. Mid-crustal melting triggered southward ductile extrusion (channel flow) of a mid-crustal layer bounded by a crustal-scale thrust fault and shear zone (Main Central Thrust; MCT) along the base, and a low-angle ductile shear zone and normal fault (South Tibetan Detachment; STD) along the top. Multi-system thermochronology (U–Pb, Sm–Nd, 40Ar–39Ar and fission track dating) show that partial melting spanned ̃24–15 Ma and triggered mid-crustal flow between the simultaneously active shear zones of the MCT and STD. Granite melting was restricted in both time (Early Miocene) and space (middle crust) along the entire length of the Himalaya. Melts were channelled up via hydraulic fracturing into sheeted sill complexes from the underthrust Indian plate source beneath southern Tibet, and intruded for up to 100 km parallel to the foliation in the host sillimanite gneisses. Crystallisation of the leucogranites was immediately followed by rapid exhumation, cooling and enhanced erosion during the Early–Middle Miocene.

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33

Eugster, Patricia, Rasmus C. Thiede, Dirk Scherler, Konstanze Stübner, Edward R. Sobel, and Manfred R. Strecker. "Segmentation of the Main Himalayan Thrust Revealed by Low-Temperature Thermochronometry in the Western Indian Himalaya." Tectonics 37, no. 8 (2018): 2710–26. http://dx.doi.org/10.1029/2017tc004752.

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34

Hazarika, Devajit, Somak Hajra, Abhishek Kundu, Meena Bankhwal, Naresh Kumar, and C. C. Pant. "Imaging the Moho and Main Himalayan Thrust beneath the Kumaon Himalaya: constraints from receiver function analysis." Geophysical Journal International 224, no. 2 (2020): 858–70. http://dx.doi.org/10.1093/gji/ggaa478.

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SUMMARY We analyse P-wave receiver functions across the Kumaon Himalaya and adjoining area to constrain crustal thickness, intracrustal structures and seismic velocity characteristics to address the role of the underlying structure on seismogenesis and geodynamic evolution of the region. The three-component waveforms of teleseismic earthquakes recorded by a seismological network consisting of 18 broad-band seismological stations have been used for receiver function analysis. The common conversion point (CCP) depth migrated receiver function image and shear wave velocity models obtained through inversion show a variation of crustal thickness from ∼38 km in the Indo-Gangetic Plain to ∼42 km near the Vaikrita Thrust. A ramp (∼20°) structure on the Main Himalayan Thrust (MHT) is revealed beneath the Chiplakot Crystalline Belt (CCB) that facilitates the exhumation of the CCB. The geometry of the MHT observed from the receiver function image is consistent with the geometry revealed by a geological balanced cross-section. A cluster of seismicity at shallow to mid-crustal depths is detected near the MHT ramp. The spatial and depth distribution of seismicity pattern beneath the CCB and presence of steep dipping imbricate faults inferred from focal mechanism solutions suggest a Lesser Himalayan Duplex structure in the CCB above the MHT ramp. The study reveals a low-velocity zone (LVZ) with a high Poisson's ratio (σ ∼0.28–0.30) at lower crustal depth beneath the CCB. The high value of Poisson's ratio in the lower crust suggests the presence of fluid/partial melt. The shear heating in the ductile regime and/or decompression and cooling associated with the exhumation of the CCB plausibly created favorable conditions for partial melting in the lower crustal LVZ.

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35

Wesnousky, Steven G., Yasuhiro Kumahara, Deepak Chamlagain, and Prajwal Chandra Neupane. "Large Himalayan Frontal Thrust paleoearthquake at Khayarmara in eastern Nepal." Journal of Asian Earth Sciences 174 (May 2019): 346–51. http://dx.doi.org/10.1016/j.jseaes.2019.01.008.

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36

Blisniuk, Peter M., Leslie J. Sonder, and Robert J. Lillie. "Foreland normal fault control on northwest Himalayan thrust front development." Tectonics 17, no. 5 (1998): 766–79. http://dx.doi.org/10.1029/98tc01870.

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37

Baker, Dan M., Robert J. Lillie, Robert S. Yeats, Gary D. Johnson, Mohammad Yousuf, and Agha Sher Hamid Zamin. "Development of the Himalayan frontal thrust zone: Salt Range, Pakistan." Geology 16, no. 1 (1988): 3. http://dx.doi.org/10.1130/0091-7613(1988)016<0003:dothft>2.3.co;2.

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38

Wesnousky, Steven G., Senthil Kumar, R. Mohindra, and V. C. Thakur. "Uplift and convergence along the Himalayan Frontal Thrust of India." Tectonics 18, no. 6 (1999): 967–76. http://dx.doi.org/10.1029/1999tc900026.

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39

Kumar, S. "Earthquake Recurrence and Rupture Dynamics of Himalayan Frontal Thrust, India." Science 294, no. 5550 (2001): 2328–31. http://dx.doi.org/10.1126/science.1066195.

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40

Martin, Aaron J. "A review of definitions of the Himalayan Main Central Thrust." International Journal of Earth Sciences 106, no. 6 (2016): 2131–45. http://dx.doi.org/10.1007/s00531-016-1419-8.

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41

Treloar, Peter J., Richard M. Palin, and Michael P. Searle. "Towards resolving the metamorphic enigma of the Indian Plate in the NW Himalaya of Pakistan." Geological Society, London, Special Publications 483, no. 1 (2019): 255–79. http://dx.doi.org/10.1144/sp483-2019-22.

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AbstractThe Pakistan part of the Himalaya has major differences in tectonic evolution compared with the main Himalayan range to the east of the Nanga Parbat syntaxis. There is no equivalent of the Tethyan Himalaya sedimentary sequence south of the Indus–Tsangpo suture zone, no equivalent of the Main Central Thrust, and no Miocene metamorphism and leucogranite emplacement. The Kohistan Arc was thrust southward onto the leading edge of continental India. All rocks exposed to the south of the arc in the footwall of the Main Mantle Thrust preserve metamorphic histories. However, these do not all record Cenozoic metamorphism. Basement rocks record Paleo-Proterozoic metamorphism with no Cenozoic heating; Neo-Proterozoic through Cambrian sediments record Ordovician ages for peak kyanite and sillimanite grade metamorphism, although Ar–Ar data indicate a Cenozoic thermal imprint which did not reset the peak metamorphic assemblages. The only rocks that clearly record Cenozoic metamorphism are Upper Paleozoic through Mesozoic cover sediments. Thermobarometric data suggest burial of these rocks along a clockwise pressure–temperature path to pressure–temperature conditions of c. 10–11 kbar and c. 700°C. Resolving this enigma is challenging but implies downward heating into the Indian plate, coupled with later development of unconformity parallel shear zones that detach Upper Paleozoic–Cenozoic cover rocks from Neoproterozoic to Paleozoic basement rocks and also detach those rocks from the Paleoproterozoic basement.

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42

Thapa, Sandeep, Shashi Tamang, Kabi Raj Paudyal, Frédéric Girault, and Frédéric Perrier. "Geology and micro-structure analysis of the MCT zone along Khudi- Bahundanda area of Lamjung District, west-central Nepal." Journal of Nepal Geological Society 58 (June 25, 2019): 105–10. http://dx.doi.org/10.3126/jngs.v58i0.24593.

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Geological mapping was carried out along the Marsyangdi Valley in the Khudi-Bahundanda area of west-central Nepal covering the Main Central Thrust (MCT) zone. The main objectives of the study were to draw a clear picture of lithology, geological structures and micro-tectonics in the rocks. A detail survey on stratigraphy and correlation with central Nepal reveals geological rock units such as the Benighat Slate, the Malekhu Formation and the Robang Formation of the Lesser Himalaya and the Formation I of the Higher Himalaya. Both regional and small-scale geological structures have been studied. The MCT zone has been mapped as a major regional structure in the region. The Bahundanda Thrust (BT), which has brought the older Malekhu Formation over the younger Robang Formation, is an another significant structure mapped. The BT is marked on the basis of fault breccia, slickensides as well as large deposits of debris mass at the fault zone. The study area has undergone poly-metamorphism and dynamic crystallization of minerals. The Lesser Himalayan rocks resemble the garnet zone while the Higher Himalaya rocks resemble to the kyanite grade of metamorphism. The present section clearly shows the inverted metamorphism in the MCT zone as in the other sections of the Himalaya. Microscopic features like ribbon-quartz, polygonization of quartz crystals, grain boundary reduction, mica-fish and rotated garnet grains indicates the ductile shearing in the MCT zone suggesting the dynamic recrystallization during thrust propagation. Numerous outcrop-scale structures like meso-scalefolds, quartz veins, boudinage and ptygmatic folds are abundant folds in the MCT zone and these are mostly E-W trending.

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Pearson, Ofori N., and Peter G. DeCelles. "Structural geology and regional tectonic significance of the Ramgarh thrust, Himalayan fold-thrust belt of Nepal." Tectonics 24, no. 4 (2005): n/a. http://dx.doi.org/10.1029/2003tc001617.

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Rawat, Gautam, G. Philip, N. Suresh, Medha, and Rekha Yadav. "Electrical resistivity tomography along the Himalayan Frontal Thrust in the northwestern Frontal Himalaya for active tectonics studies." Modeling Earth Systems and Environment 5, no. 4 (2019): 1563–68. http://dx.doi.org/10.1007/s40808-019-00604-z.

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45

Luirei, Khayingshing, Surendra S. Bhakuni, and Girish Ch Kothyari. "Drainage response to active tectonics and evolution of tectonic geomorphology across the Himalayan Frontal Thrust, Kumaun Himalaya." Geomorphology 239 (June 2015): 58–72. http://dx.doi.org/10.1016/j.geomorph.2015.03.011.

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46

Hubbard, Mary, David R. Lageson, and Roshan Raj Bhattarai. "Reactivated normal-sense shear zones in the core of the Greater Himalayan Sequence, Solukhumbu District, Nepal." Journal of Nepal Geological Society 53 (December 31, 2017): 99–105. http://dx.doi.org/10.3126/jngs.v53i0.23823.

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We present preliminary observations from the Solukhumbu region of Nepal, coupled with structures described in the literature, to suggest the importance of structural and metamorphic discontinuities within the Himalayan metamorphic core (Greater Himalayan Sequence) and reactivation of at least one of these thrust discontinuities with a normal (down-to-the-north) sense of displacement. Based on preliminary geochronologic data, development of these discontinuities may have evolved over time. In the Dudh Kosi Valley near Ghat, gneissic rocks and pegmatites exhibit tectonized fabrics and yield argon cooling ages of ~4 Ma for K-feldspar and ~9 Ma for biotite. Just north of Khumjung there is a prominent topographic break from which sheared gneissic rocks indicate a top-to-the-north, or normal, sense of shear. Near Pangboche, a repeated section of kyanitebearing rocks interleaved with sillimanite-muscovite schist suggests structural imbrication and/or interleaved retrograde metamorphism. Below the peaks of Nuptse and Lhotse, the Khumbu thrust (Searle 1999) appears to form the floor of a thick succession of leucogranite sills. We suggest that these discontinuities were formed over time, possibly from early MCT and STDS deformation at ~21 Ma to as recent as ~4 Ma, and need to be considered in kinematic models that combine channel flow with critical taper and tectonic denudation. Moreover, orogenic collapse in the Himalayan core may be migrating southward through time as the orogenic wedge continues to uplift in response to underthrusting of India and southward propagation of the Main Frontal Thrust system.

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Matin, Abdul, and Malay Mukul. "Himalayan cross faults affect thrust sheet geometry: An example from the Munsiari thrust sheet near the Gish Transverse fault zone, frontal Darjiling Himalaya, India." Journal of Asian Earth Sciences 199 (September 2020): 104400. http://dx.doi.org/10.1016/j.jseaes.2020.104400.

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48

Sengör, A. M. C. "Evolution of thought on thrust faulting and the Alpine-Himalayan system." Geologiska Föreningen i Stockholm Förhandlingar 110, no. 4 (1988): 416. http://dx.doi.org/10.1080/11035898809452692.

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Dubey, Ashok K., and Surendra S. Bhakuni. "Younger hanging wall rocks along the Vaikrita Thrust of the High Himalaya: A model based on inversion tectonics." Himalayan Journal of Sciences 2, no. 4 (2008): 129. http://dx.doi.org/10.3126/hjs.v2i4.831.

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50

Laporte, M., L. Bollinger, H. Lyon-Caen, et al. "Seismicity in far western Nepal reveals flats and ramps along the Main Himalayan Thrust." Geophysical Journal International 226, no. 3 (2021): 1747–63. http://dx.doi.org/10.1093/gji/ggab159.

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SUMMARY Unravelling relations between lateral variations of mid-crustal seismicity and the geometry of the Main Himalayan Thrust (MHT) system at depth is a key issue in seismotectonic studies of the Himalayan range. These relations can reveal along strike changes in the behaviour of the fault at depth related to fluids or the local ramp-flat geometry and more generally of the stress build-up along the fault. Some of these variations may control the rupture extension of intermediate, large or great earthquakes, the last of which dates back from 1505 CE in far western Nepal. The region is also associated to lateral spatio-temporal variations of the mid-crustal seismicity monitored by the Regional Seismic Network of Surkhet–Birendranagar. This network was supplemented between 2014 and 2016 by 15 temporary stations deployed above the main seismic clusters giving new potential to regional studies. Both absolute and relative locations together with focal mechanisms are determined to gain insight on the fault behaviour at depth. We find more than 4000 earthquakes within 5 and 20 km-depth clustered in three belts parallel to the front of the Himalayan range. Finest locations reveal close relationships between seismic clusters and fault segments at depth among which mid-crustal ramps and reactivated tectonic slivers. Our results support a geometry of the MHT involving several fault patches at depth separated by ramps and tear faults. This geometry most probably affects the pattern of the coseismic ruptures breaking partially or totally the locked fault zone as well as eventual along strike variations of seismic coupling during interseismic period.

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Journal articles on the topic 'Himalayan Thrust'

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