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Jean-philippe Avouac - One of the best experts on this subject based on the ideXlab platform.
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exhumation crustal deformation and thermal structure of the nepal himalaya derived from the inversion of thermochronological and thermobarometric data and modeling of the topography
Journal of Geophysical Research, 2010Co-Authors: Laurent Bollinger, Jean-philippe Avouac, Frederic Herman, Peter Copeland, Gweltaz Maheo, Patrick Le Fort, David A Foster, Arnaud Pecher, Kurt StuweAbstract:duplex initiated at 9.8 ± 1.7 Ma, leading to an increase of uplift rate at front of the High Himalaya from 0.9 ± 0.31 to 3.05 ± 0.9 mm yr −1 . We also run 3‐D models by coupling PECUBE with a landscape evolution model (CASCADE). This modeling shows that the effectoftheevolvingtopographycanexplainafractionofthescatterobservedinthedatabut not all of it, suggesting that lateral variations of the kinematics of crustal deformation and exhumationarelikely.Ithasbeenarguedthatthesteepphysiographictransitionatthefootof the Greater Himalayan Sequence indicates OOS thrusting, but our results demonstrate that the best fit duplex model derived from the thermochronological and thermobarometric data reproduces the present morphology of the Nepal Himalaya equally well.
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Mountain building in the Nepal Himalaya: Thermal and kinematic model
Earth and Planetary Science Letters, 2006Co-Authors: Laurent Bollinger, P. Henry, Jean-philippe AvouacAbstract:We model crustal deformation and the resulting thermal structure across the Nepal Himalaya, assuming that, since 20 Ma, shortening across the range has been primarily taken up by slip along a single thrust fault, the Main Himalayan Thrust (MHT) Fault, and that the growth of the Himalayan wedge has resulted mainly from underplating and to the development of a duplex at midcrustal depth. We show that this process can account for the inverse thermal metamorphic gradient documented throughout the Lesser Himalaya (LH), the discontinuity of peak metamorphic temperatures across the MCT, as well as the distribution of age of exhumation across the range. This study suggests that the metamorphic evolution of the range over about the last 20 million years is compatible with the kinematics of recent crustal deformation deduced from morphotectonic and geodetic studies. © 2006 Elsevier B.V. All rights reserved.
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fluvial incision and tectonic uplift across the Himalayas of central nepal
Journal of Geophysical Research, 2001Co-Authors: Jérôme Lavé, Jean-philippe AvouacAbstract:The pattern of fluvial incision across the Himalayas of central Nepal is estimated from the distribution of Holocene and Pleistocene terraces and from the geometry of modern channels along major rivers draining across the range. The terraces provide good constraints on incision rates across the Himalayan frontal folds (Sub-Himalaya or Siwaliks Hills) where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces. Farther north and upstream, in the Lesser Himalaya, prominent fill terraces were deposited, probably during the late Pleistocene, and were subsequently incised. The amount of bedrock incision beneath the fill deposits is generally small, suggesting a slow rate of fluvial incision in the Lesser Himalaya. The terrace record is lost in the high range where the rivers are cutting steep gorges. To complement the terrace study, fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate. This approach allows quantification of the effect of variations in channel slope, width, and discharge on the incision rate of a river; the determination of incision rates requires an additional lithological calibration. The two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared. In the Sub-Himalaya, river incision is rapid, with values up to 10–15 mm/yr. It does not exceed a few millimeters per year in the Lesser Himalaya, and rises abruptly at the front of the high range to reach values of ∼4–8 mm/yr within a 50-km-wide zone that coincides with the position of the highest Himalayan peaks. Sediment yield derived from the measurement of suspended load in Himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range. The observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat-ramp-flat geometry of the Main Himalayan Thrust fault. The morphology of the range reflects a dynamic equilibrium between present-day tectonics and surface processes. The sharp relief together with the high uplift rates in the Higher Himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the Tibetan Plateau driven by late Cenozoic climate change, or late Miocene reactivation of the Main Central Thrust.
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Le cycle sismique en Himalaya
Comptes Rendus de l'Academie de Sciences - Serie IIa: Sciences de la Terre et des Planetes, 2001Co-Authors: Jean-philippe Avouac, Jérôme Lavé, Laurent Bollinger, R. Cattin, Mireille FlouzatAbstract:We discuss the seismic cycle in the Himalayas and its relation to mountain building on the basis of geodetic, seismological and geological data collected in the Himalaya of Nepal. On average over several seismic cycles, localized slip on a major thrust fault, the Main Himalayan Thrust fault, MHT, accommodates the ~ 21 mm·yr-1convergence rate between southern Tibet and India. The geodetic data show that the MHT is presently locked from the sub-Himalayas to beneath the front of the high range where it roots into a sub-horizontal ductile shear zone under southern Tibet. Aseismic slip during the interseismic period induces stress accumulation at the southern edge of this shear zone triggering intense microseismic activity and elastic straining of the upper crust at the front of the high range. This deformation is released, on the long term, by major earthquakes on the MHT. Such an event is the Mw8.4-1934-earthquake that ruptured a 250-300-km long segment. The major seismic events along the Himalayas since the 19th century have released more than 70 % of the crustal strain accumulated over that period, suggesting that, if any, aseismic slip on the MHT cannot account for more than 30 % of the total slip. © 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS.
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active folding of fluvial terraces across the siwaliks hills Himalayas of central nepal
Journal of Geophysical Research, 2000Co-Authors: Jérôme Lavé, Jean-philippe AvouacAbstract:We analyze geomorphic evidence of recent crustal deformation in the sub-Himalaya of central Nepal, south of the Kathmandu Basin. The Main Frontal Thrust fault (MFT), which marks the southern edge of the sub-Himalayan fold belt, is the only active structure in that area. Active fault bend folding at the MFT is quantified from structural geology and fluvial terraces along the Bagmati and Bakeya Rivers. Two major and two minor strath terraces are recognized and dated to be 9.2, 2.2, and 6.2, 3.7 calibrated (cal) kyr old, respectively. Rock uplift of up to 1.5 cm/yr is derived from river incision, accounting for sedimentation in the Gangetic plain and channel geometry changes. Rock uplift profiles are found to correlate with bedding dip angles, as expected in fault bend folding. It implies that thrusting along the MFT has absorbed 21 ± 1.5 mm/yr of N-S shortening on average over the Holocene period. The ±1.5 mm/yr defines the 68% confidence interval and accounts for uncertainties in age, elevation measurements, initial geometry of the deformed terraces, and seismic cycle. At the longitude of Kathmandu, localized thrusting along the Main Frontal Thrust fault must absorb most of the shortening across the Himalaya. By contrast, microseismicity and geodetic monitoring over the last decade suggest that interseismic strain is accumulating beneath the High Himalaya, 50–100 km north of the active fold zone, where the Main Himalayan Thrust (MHT) fault roots into a ductile decollement beneath southern Tibet. In the interseismic period the MHT is locked, and elastic deformation accumulates until being released by large (M_w > 8) earthquakes. These earthquakes break the MHT up to the near surface at the front of the Himalayan foothills and result in incremental activation of the MFT.
Delores M Robinson - One of the best experts on this subject based on the ideXlab platform.
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Was Himalayan normal faulting triggered by initiation of the Ramgarh–Munsiari thrust and development of the Lesser Himalayan duplex?
International Journal of Earth Sciences, 2013Co-Authors: Delores M Robinson, Ofori N. PearsonAbstract:The Ramgarh–Munsiari thrust is a major orogen-scale fault that extends for more than 1,500 km along strike in the Himalayan fold-thrust belt. The fault can be traced along the Himalayan arc from Himachal Pradesh, India, in the west to eastern Bhutan. The fault is located within the Lesser Himalayan tectonostratigraphic zone, and it translated Paleoproterozoic Lesser Himalayan rocks more than 100 km toward the foreland. The Ramgarh–Munsiari thrust is always located in the proximal footwall of the Main Central thrust. Northern exposures (toward the hinterland) of the thrust sheet occur in the footwall of the Main Central thrust at the base of the high Himalaya, and southern exposures (toward the foreland) occur between the Main Boundary thrust and Greater Himalayan klippen. Although the metamorphic grade of rocks within the Ramgarh–Munsiari thrust sheet is not significantly different from that of Greater Himalayan rock in the hanging wall of the overlying Main Central thrust sheet, the tectonostratigraphic origin of the two different thrust sheets is markedly different. The Ramgarh–Munsiari thrust became active in early Miocene time and acted as the roof thrust for a duplex system within Lesser Himalayan rocks. The process of slip transfer from the Main Central thrust to the Ramgarh–Munsiari thrust in early Miocene time and subsequent development of the Lesser Himalayan duplex may have played a role in triggering normal faulting along the South Tibetan Detachment system.
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upper crustal shortening and forward modeling of the himalayan thrust belt along the budhi gandaki river central nepal
International Journal of Earth Sciences, 2013Co-Authors: Subodha Khanal, Delores M RobinsonAbstract:A balanced cross-section along the Budhi-Gandaki River in central Nepal between the Main Central thrust, including displacement on that fault, and the Main Frontal thrust reveals a minimum total shortening of 400 km. Minimum displacement on major orogen-scale structures include 116 km on the Main Central thrust, 110 km on the Ramgarh thrust, 95 km on the Trishuli thrust, and 56 km in the Lesser Himalayan duplex. The balanced cross-section was also incrementally forward modeled assuming a generally forward-breaking sequence of thrusting, where early faults and hanging-wall structures are passively carried from the hinterland toward the foreland. The approximate correspondence of the forward modeled result to observe present day geometries suggest that the section interpretation is viable and admissible. In the balanced cross-section, the Trishuli thrust is the roof thrust for the Lesser Himalayan duplex. The forward model and reconstruction emphasize that the Lesser Himalayan duplex grew by incorporating rock from the footwall and transferring it to the hanging wall along the Main Himalayan thrust. As the duplex developed, the Lesser Himalayan ramp migrated southward. The movement of Lesser Himalayan thrust sheets over the ramp pushed the Lesser Himalayan rock and the overburdens of the Greater and Tibetan Himalayan rock toward the erosional surface. This vertical structural movement caused by footwall collapse and duplexing, in combination with erosion, exhumed the Lesser Himalaya.
Kazunori Arita - One of the best experts on this subject based on the ideXlab platform.
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thrust tectonics crustal shortening and the structure of the far eastern nepal himalaya
Tectonics, 1991Co-Authors: Daniel Schelling, Kazunori AritaAbstract:Balanced and restored structural sections across the far-eastern Nepal Himalaya have been constructed in order to determine the structure and evolution of the Himalayan orogenic wedge and the amount of tectonic shortening the region has undergone since the initiation of thrusting along the Main Central Thrust (MCT). The far-eastern Nepal Himalaya is comprised of three distinct, thrust-bound tectonic packages; the Higher Himalayan (Crystalline) thrust sheet, the Lesser Himalayan (Metasediment) thrust package, and the Sub-Himalayan imbricate fan. The Higher Himalayan Crystallines, consisting of kyanite- and sillimanite-bearing gneisses intruded by the Miocene (?) Jannu leucogranites, have been thrust over the Lesser Himalayan Metasediments along the MCT for a distance of 140 km to 175 km. The Lesser Himalayan Metasediments are a 12 km thick unit consisting primarily of phyllites, metaquartzites, and mylonitic augen gneisses in which garnet, biotite and chlorite metamorphic zones are exposed in progressively deeper structural levels. The Lesser Himalayan (Metasediment) thrust package is underlain by a decollement, the Main Detachment Fault (MDF), which lies at a calculated depth of between 6 and 10 km underneath the Mahabharat Lekh, and at a calculated depth of 20 to 25 km north of the Tamar Khola Dome. The Tamar Khola Dome overlies a footwall ramp along the MDF where the MDF cuts upsection through the Lesser Himalayan Metasediments. The Lesser Himalayan thrust package probably has an internal structure aproximating a hinterland-dipping duplex, with the MCT and the MDF corresponding to the roof and floor thrusts, respectively. Both the Tamar Khola Thrust, an out-of-sequence breach thrust, and the Main Boundary Thrust (MBT) are splay thrusts off of the MDF. The Sub-Himalaya, consisting of nonmetamorphosed sedimentary rocks, displays an emergent imbricate fan geometry and is underlain by the southern continuation of the MDF which lies at a depth of 5.5 km to 6 km beneath the Siwalik Hills. Folding and thrusting within the Lesser Himalayan thrust package and the Sub-Himalayan imbricate fan have accomodated 45 to 70 km of tectonic shortening. Total north-south shortening across the Higher, Lesser, and Sub-Himalaya of far-eastern Nepal, south of the Tibetan Plateau, has been of the order of 185 km to 245 km and has occurred at an average rate of 7.4 mm to 15.3 mm per year since the initiation of the MCT between 16 and 25 Ma.
Megh Raj Dhital - One of the best experts on this subject based on the ideXlab platform.
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Geology of the Nepal Himalaya: Regional perspective of the classic collided orogen
Geology of the Nepal Himalaya: Regional Perspective of the Classic Collided Orogen, 2015Co-Authors: Megh Raj DhitalAbstract:This book addresses the geology of the entire Himalayan range in Nepal, i.e., from the Gangetic plain in the south to the Tethyan zone in the north. Without a comprehensive look at the various Himalayan zones, it is practically impossible to fully grasp the processes at work behind the formation and development of the spectacular Himalaya. However, the goal is not merely to document all the scientific ontology but rather to reveal a sound basis for the prevailing concepts. Both the early literature on Himalayan geology and contemporary trends are fully covered. For the first time, the origin, use, and abuse of common Himalayan geological terms such as the Siwaliks, Lesser Himalaya, Main Boundary Thrust, Main Central Thrust, and Tethys are discussed. The book will help readers to progress from a cognitive approach to a constructive one by linking various types of knowledge, such as seeking relations between various geological structures as well as between earlier thoughts or views and contemporary approaches. Chapter 1 Introduction -- Part 1 Geological Setting and Physiography -- 2 Geological Setting of Himalaya -- 3 Physiography of Nepal -- Part 2 Geology of Neighbouring Regions -- 4 Northwest Himalaya -- 5 Southeast Himalaya and Adjacent Indian Peninsula -- Part 3 Lesser Himalaya -- 6 Introduction to Lesser Himalaya -- 7 Lesser Himalaya of Mahakali?Seti region -- 8 Lesser Himalaya of Karnali?Bheri region -- 9 Lesser Himalaya of Gandaki region -- 10 Lesser Himalaya of Bagmati?Gosainkund region -- 11 Lesser Himalaya of Koshi region -- 12 Lesser Himalaya of Arun?Tamar region -- Part 4 Higher Himalaya -- 13 Introduction to Higher Himalaya -- 14 Higher Himalaya of Mahakali?Seti region -- 15 Higher Himalaya of Karnali?Bheri region -- 16 Higher Himalaya of Gandaki region -- 17 Higher Himalaya of Bagmati?Gosainkund region -- 18 Higher Himalaya of Koshi region -- 19 Higher Himalaya of Arun?Tamar region.- 20 Models of Himalayan metamorphism -- Part 5 Tethys Himalaya -- 21 Introduction to Tethys Himalaya -- 22 Tethys Himalaya of Mahakali region -- 23 Tethys Himalaya of Karnali?Bheri region (Dolpa) -- 24 Tethys Himalaya of Ganaki region (Thakkhola) -- 25 Tethys Himalaya of Gandaki region (Manang) -- 26 Tethys Himalaya of Koshi region (Mount Everest and neighbourhood) -- Part 6 Siwaliks -- 27 Introduction to Siwaliks -- 28 Siwaliks of Mahakali?Seti region -- 29 Siwaliks of Karnali?Bheri region -- 30 Siwaliks of Gandaki region -- 31 Siwaliks of Bagmati?Gosainkund region -- 32 Siwaliks of Koshi region -- 33 Siwaliks of Arun?Tamar region -- Part 7 Terai, intermontane basins, and neotectonics -- 34 Terai and intermontane basins -- 35 Neotectonics -- 36 Conclusions.
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Physiography of Nepal
2015Co-Authors: Megh Raj DhitalAbstract:This book addresses the geology of the entire Himalayan range in Nepal, i.e., from the Gangetic plain in the south to the Tethyan zone in the north. Without a comprehensive look at the various Himalayan zones, it is practically impossible to fully grasp the processes at work behind the formation and development of the spectacular Himalaya. However, the goal is not merely to document all the scientific ontology but rather to reveal a sound basis for the prevailing concepts. Both the early literature on Himalayan geology and contemporary trends are fully covered. For the first time, the origin, use, and abuse of common Himalayan geological terms such as the Siwaliks, Lesser Himalaya, Main Boundary Thrust, Main Central Thrust, and Tethys are discussed. The book will help readers to progress from a cognitive approach to a constructive one by linking various types of knowledge, such as seeking relations between various geological structures as well as between earlier thoughts or views and contemporary approaches. Chapter 1 Introduction -- Part 1 Geological Setting and Physiography -- 2 Geological Setting of Himalaya -- 3 Physiography of Nepal -- Part 2 Geology of Neighbouring Regions -- 4 Northwest Himalaya -- 5 Southeast Himalaya and Adjacent Indian Peninsula -- Part 3 Lesser Himalaya -- 6 Introduction to Lesser Himalaya -- 7 Lesser Himalaya of Mahakali?Seti region -- 8 Lesser Himalaya of Karnali?Bheri region -- 9 Lesser Himalaya of Gandaki region -- 10 Lesser Himalaya of Bagmati?Gosainkund region -- 11 Lesser Himalaya of Koshi region -- 12 Lesser Himalaya of Arun?Tamar region -- Part 4 Higher Himalaya -- 13 Introduction to Higher Himalaya -- 14 Higher Himalaya of Mahakali?Seti region -- 15 Higher Himalaya of Karnali?Bheri region -- 16 Higher Himalaya of Gandaki region -- 17 Higher Himalaya of Bagmati?Gosainkund region -- 18 Higher Himalaya of Koshi region -- 19 Higher Himalaya of Arun?Tamar region.- 20 Models of Himalayan metamorphism -- Part 5 Tethys Himalaya -- 21 Introduction to Tethys Himalaya -- 22 Tethys Himalaya of Mahakali region -- 23 Tethys Himalaya of Karnali?Bheri region (Dolpa) -- 24 Tethys Himalaya of Ganaki region (Thakkhola) -- 25 Tethys Himalaya of Gandaki region (Manang) -- 26 Tethys Himalaya of Koshi region (Mount Everest and neighbourhood) -- Part 6 Siwaliks -- 27 Introduction to Siwaliks -- 28 Siwaliks of Mahakali?Seti region -- 29 Siwaliks of Karnali?Bheri region -- 30 Siwaliks of Gandaki region -- 31 Siwaliks of Bagmati?Gosainkund region -- 32 Siwaliks of Koshi region -- 33 Siwaliks of Arun?Tamar region -- Part 7 Terai, intermontane basins, and neotectonics -- 34 Terai and intermontane basins -- 35 Neotectonics -- 36 Conclusions.
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Models of Himalayan Metamorphism
2015Co-Authors: Megh Raj DhitalAbstract:This book addresses the geology of the entire Himalayan range in Nepal, i.e., from the Gangetic plain in the south to the Tethyan zone in the north. Without a comprehensive look at the various Himalayan zones, it is practically impossible to fully grasp the processes at work behind the formation and development of the spectacular Himalaya. However, the goal is not merely to document all the scientific ontology but rather to reveal a sound basis for the prevailing concepts. Both the early literature on Himalayan geology and contemporary trends are fully covered. For the first time, the origin, use, and abuse of common Himalayan geological terms such as the Siwaliks, Lesser Himalaya, Main Boundary Thrust, Main Central Thrust, and Tethys are discussed. The book will help readers to progress from a cognitive approach to a constructive one by linking various types of knowledge, such as seeking relations between various geological structures as well as between earlier thoughts or views and contemporary approaches. Chapter 1 Introduction -- Part 1 Geological Setting and Physiography -- 2 Geological Setting of Himalaya -- 3 Physiography of Nepal -- Part 2 Geology of Neighbouring Regions -- 4 Northwest Himalaya -- 5 Southeast Himalaya and Adjacent Indian Peninsula -- Part 3 Lesser Himalaya -- 6 Introduction to Lesser Himalaya -- 7 Lesser Himalaya of Mahakali?Seti region -- 8 Lesser Himalaya of Karnali?Bheri region -- 9 Lesser Himalaya of Gandaki region -- 10 Lesser Himalaya of Bagmati?Gosainkund region -- 11 Lesser Himalaya of Koshi region -- 12 Lesser Himalaya of Arun?Tamar region -- Part 4 Higher Himalaya -- 13 Introduction to Higher Himalaya -- 14 Higher Himalaya of Mahakali?Seti region -- 15 Higher Himalaya of Karnali?Bheri region -- 16 Higher Himalaya of Gandaki region -- 17 Higher Himalaya of Bagmati?Gosainkund region -- 18 Higher Himalaya of Koshi region -- 19 Higher Himalaya of Arun?Tamar region.- 20 Models of Himalayan metamorphism -- Part 5 Tethys Himalaya -- 21 Introduction to Tethys Himalaya -- 22 Tethys Himalaya of Mahakali region -- 23 Tethys Himalaya of Karnali?Bheri region (Dolpa) -- 24 Tethys Himalaya of Ganaki region (Thakkhola) -- 25 Tethys Himalaya of Gandaki region (Manang) -- 26 Tethys Himalaya of Koshi region (Mount Everest and neighbourhood) -- Part 6 Siwaliks -- 27 Introduction to Siwaliks -- 28 Siwaliks of Mahakali?Seti region -- 29 Siwaliks of Karnali?Bheri region -- 30 Siwaliks of Gandaki region -- 31 Siwaliks of Bagmati?Gosainkund region -- 32 Siwaliks of Koshi region -- 33 Siwaliks of Arun?Tamar region -- Part 7 Terai, intermontane basins, and neotectonics -- 34 Terai and intermontane basins -- 35 Neotectonics -- 36 Conclusions.
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Introduction to Siwaliks
2015Co-Authors: Megh Raj DhitalAbstract:This book addresses the geology of the entire Himalayan range in Nepal, i.e., from the Gangetic plain in the south to the Tethyan zone in the north. Without a comprehensive look at the various Himalayan zones, it is practically impossible to fully grasp the processes at work behind the formation and development of the spectacular Himalaya. However, the goal is not merely to document all the scientific ontology but rather to reveal a sound basis for the prevailing concepts. Both the early literature on Himalayan geology and contemporary trends are fully covered. For the first time, the origin, use, and abuse of common Himalayan geological terms such as the Siwaliks, Lesser Himalaya, Main Boundary Thrust, Main Central Thrust, and Tethys are discussed. The book will help readers to progress from a cognitive approach to a constructive one by linking various types of knowledge, such as seeking relations between various geological structures as well as between earlier thoughts or views and contemporary approaches. Chapter 1 Introduction -- Part 1 Geological Setting and Physiography -- 2 Geological Setting of Himalaya -- 3 Physiography of Nepal -- Part 2 Geology of Neighbouring Regions -- 4 Northwest Himalaya -- 5 Southeast Himalaya and Adjacent Indian Peninsula -- Part 3 Lesser Himalaya -- 6 Introduction to Lesser Himalaya -- 7 Lesser Himalaya of Mahakali?Seti region -- 8 Lesser Himalaya of Karnali?Bheri region -- 9 Lesser Himalaya of Gandaki region -- 10 Lesser Himalaya of Bagmati?Gosainkund region -- 11 Lesser Himalaya of Koshi region -- 12 Lesser Himalaya of Arun?Tamar region -- Part 4 Higher Himalaya -- 13 Introduction to Higher Himalaya -- 14 Higher Himalaya of Mahakali?Seti region -- 15 Higher Himalaya of Karnali?Bheri region -- 16 Higher Himalaya of Gandaki region -- 17 Higher Himalaya of Bagmati?Gosainkund region -- 18 Higher Himalaya of Koshi region -- 19 Higher Himalaya of Arun?Tamar region.- 20 Models of Himalayan metamorphism -- Part 5 Tethys Himalaya -- 21 Introduction to Tethys Himalaya -- 22 Tethys Himalaya of Mahakali region -- 23 Tethys Himalaya of Karnali?Bheri region (Dolpa) -- 24 Tethys Himalaya of Ganaki region (Thakkhola) -- 25 Tethys Himalaya of Gandaki region (Manang) -- 26 Tethys Himalaya of Koshi region (Mount Everest and neighbourhood) -- Part 6 Siwaliks -- 27 Introduction to Siwaliks -- 28 Siwaliks of Mahakali?Seti region -- 29 Siwaliks of Karnali?Bheri region -- 30 Siwaliks of Gandaki region -- 31 Siwaliks of Bagmati?Gosainkund region -- 32 Siwaliks of Koshi region -- 33 Siwaliks of Arun?Tamar region -- Part 7 Terai, intermontane basins, and neotectonics -- 34 Terai and intermontane basins -- 35 Neotectonics -- 36 Conclusions.
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Introduction to Lesser Himalaya
2015Co-Authors: Megh Raj DhitalAbstract:This book addresses the geology of the entire Himalayan range in Nepal, i.e., from the Gangetic plain in the south to the Tethyan zone in the north. Without a comprehensive look at the various Himalayan zones, it is practically impossible to fully grasp the processes at work behind the formation and development of the spectacular Himalaya. However, the goal is not merely to document all the scientific ontology but rather to reveal a sound basis for the prevailing concepts. Both the early literature on Himalayan geology and contemporary trends are fully covered. For the first time, the origin, use, and abuse of common Himalayan geological terms such as the Siwaliks, Lesser Himalaya, Main Boundary Thrust, Main Central Thrust, and Tethys are discussed. The book will help readers to progress from a cognitive approach to a constructive one by linking various types of knowledge, such as seeking relations between various geological structures as well as between earlier thoughts or views and contemporary approaches. Chapter 1 Introduction -- Part 1 Geological Setting and Physiography -- 2 Geological Setting of Himalaya -- 3 Physiography of Nepal -- Part 2 Geology of Neighbouring Regions -- 4 Northwest Himalaya -- 5 Southeast Himalaya and Adjacent Indian Peninsula -- Part 3 Lesser Himalaya -- 6 Introduction to Lesser Himalaya -- 7 Lesser Himalaya of Mahakali?Seti region -- 8 Lesser Himalaya of Karnali?Bheri region -- 9 Lesser Himalaya of Gandaki region -- 10 Lesser Himalaya of Bagmati?Gosainkund region -- 11 Lesser Himalaya of Koshi region -- 12 Lesser Himalaya of Arun?Tamar region -- Part 4 Higher Himalaya -- 13 Introduction to Higher Himalaya -- 14 Higher Himalaya of Mahakali?Seti region -- 15 Higher Himalaya of Karnali?Bheri region -- 16 Higher Himalaya of Gandaki region -- 17 Higher Himalaya of Bagmati?Gosainkund region -- 18 Higher Himalaya of Koshi region -- 19 Higher Himalaya of Arun?Tamar region.- 20 Models of Himalayan metamorphism -- Part 5 Tethys Himalaya -- 21 Introduction to Tethys Himalaya -- 22 Tethys Himalaya of Mahakali region -- 23 Tethys Himalaya of Karnali?Bheri region (Dolpa) -- 24 Tethys Himalaya of Ganaki region (Thakkhola) -- 25 Tethys Himalaya of Gandaki region (Manang) -- 26 Tethys Himalaya of Koshi region (Mount Everest and neighbourhood) -- Part 6 Siwaliks -- 27 Introduction to Siwaliks -- 28 Siwaliks of Mahakali?Seti region -- 29 Siwaliks of Karnali?Bheri region -- 30 Siwaliks of Gandaki region -- 31 Siwaliks of Bagmati?Gosainkund region -- 32 Siwaliks of Koshi region -- 33 Siwaliks of Arun?Tamar region -- Part 7 Terai, intermontane basins, and neotectonics -- 34 Terai and intermontane basins -- 35 Neotectonics -- 36 Conclusions.
Richard Walshaw - One of the best experts on this subject based on the ideXlab platform.
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mid crustal deformation of the annapurna dhaulagiri himalaya central nepal an atypical example of channel flow during the himalayan orogeny
Geosphere, 2016Co-Authors: A J Parsons, R J Phillips, Geoffrey E Lloyd, M P Searle, Richard WalshawAbstract:The channel-flow model for the Greater Himalayan Sequence (GHS) of the Himalayan orogen involves a partially molten, rheologically weak, mid-crustal layer “flowing” southward relative to the upper and lower crust during late Oligocene–Miocene. Flow was driven by topographic overburden, underthrusting, and focused erosion. We present new structural and thermobarometric analyses from the GHS in the Annapurna-Dhaulagiri Himalaya, central Nepal; these data suggest that during exhumation, the GHS cooled, strengthened, and transformed from a weak “active channel” to a strong “channel plug” at greater depths than elsewhere in the Himalaya. After strengthening, continued convergence resulted in localized top-southwest (top-SW) shortening on the South Tibetan detachment system (STDS). The GHS in the Annapurna-Dhaulagiri Himalaya displays several geological features that distinguish it from other Himalayan regions. These include reduced volumes of leucogranite and migmatite, no evidence for partial melting within the sillimanite stability field, reduced structural thickness, and late-stage top-southwest shortening in the STDS. New and previously published structural and thermobarometric constraints suggest that the channel-flow model can be applied to mid-Eocene–early Miocene mid-crustal evolution of the GHS in the Annapurna-Dhaulagiri Himalaya. However, pressure-temperature-time (PTt) constraints indicate that following peak conditions, the GHS in this region did not undergo rapid isothermal exhumation and widespread sillimanite-grade decompression melting, as commonly recorded elsewhere in the Himalaya. Instead, lower-than-typical structural thickness and melt volumes suggest that the upper part of the GHS (Upper Greater Himalayan Sequence [UGHS]—the proposed channel) had a greater viscosity than in other Himalayan regions. We suggest that viscosity-limited, subdued channel flow prevented exhumation on an isothermal trajectory and forced the UGHS to exhume slowly. These findings are distinct from other regions in the Himalaya. As such, we describe the mid-crustal evolution of the GHS in the Annapurna-Dhaulagiri Himalaya as an atypical example of channel flow during the Himalayan orogeny.
