Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and <sup>40</sup>Ar/<sup>39</sup>Ar Thermochronology

Godin, Laurent; Parrish, Randall R.; Brown, Richard L.; Hodges, Kip

doi:10.1029/2000tc001204

Cited by 246 publications

(280 citation statements)

References 65 publications

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“…Ar/ Ar hornblende ages of c. 21 Ma from the upper part of the MCT zone south of Lukla, record the timing of cooling through the 500~ isotherm (Hubbard & Harrison 1989). Along most of the Greater Himalaya, 4~ and K-Ar muscovite and biotite ages, which record timing of cooling through 300-350~ isotherms, are always older than 14 Ma across the entire slab (Godin et al 2001). How is it possible, therefore, that 530~ metamorphic temperatures in the MCT samples with young monazite ages do not reset the 4~ and K-Ar systematics?…”

Section: Timescales Of Metamorphism Melting and Channel Flowmentioning

confidence: 99%

“…In many parts of the Garhwal and Nepal Himalaya, late-stage brittle normal faulting has cut out the flattened and sheared right-wayup isograds at the top of the GHS layer, and the STD fault places unmetamorphosed Palaeozoic sediments directly on top of sillimanite-grade gneisses and/or leucogranites (e.g. Shisha Pangma (Searle et al 1997), Garhwal ), Rongbuk valley (Hodges et al 1998;Murphy & Harrison 1999;Searle 1999a; and Annapurna (Godin et al 2001)). …”

Section: Greater Himalayan Sequencementioning

confidence: 99%

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Crustal structure, restoration and evolution of the Greater Himalaya in Nepal-South Tibet: implications for channel flow and ductile extrusion of the middle crust

2006

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Recent suggestions that the Greater Himalayan Sequence (GHS) represents a mid-crustal channel of low viscosity, partially molten Indian plate crust extruding southward between two major ductile shear zones, the Main Central thrust (MCT) below, and the South Tibetan detachment (STD) normal fault above, are examined, with particular reference to the Everest transect across Nepal-south Tibet. The catalyst for the early kyanite _ sillimanite metamorphism (650-680~ 7-8 kbar, 32-30 Ma) was crustal thickening and regional Barrovian metamorphism. Later sillimanite + cordierite metamorphism (600-680~ 4-5 kbar, 23-17 Ma) is attributed to increased heat input and partial melting of the crust. Crustal melting occurred at relatively shallow depths (15-19 km, 4-5 kbar) in the crust. The presence of highly radiogenic Proterozoic black shales (Haimanta-Cheka Groups) at this unique stratigraphic horizon promoted melting due to the high concentration of heat-producing elements, particularly U-bearing minerals. It is suggested that crustal melting triggered channel flow and ductile extrusion of the GHS, and that when the leucogranites cooled rapidly at 17-16 Ma the flow ended, as deformation propagated southward into the Lesser Himalaya. Kinematic indicators record a dominant southvergent simple shear component across the Greater Himalaya. An important component of pure shear is also recorded in flattening and boudinage fabrics within the STD zone, and compressed metamorphic isograds along both the STD and MCT shear zones. These kinematic factors suggest that the ductile GHS channel was subjected to subvertical thinning during southward extrusion. However, dating of the shear zones along the top and base of the channel shows that the deformation propagated outward with time over the period 20-16 Ma, expanding the extruding channel. The last brittle faulting episode occurred along the southern (structurally lower) limits of the MCT shear zone and the northem (structurally higher) limits of the STD normal fault zone. Late-stage breakback thrusting occurred along the MCT and at the back of the orogenic wedge in the Tethyan zone. Our model shows that the Himalayan-south Tibetan crust is rheologically layered, and has several major low-angle detachments that separate layers of crust and upper mantle, each deforming in different ways, at different times.The Tibetan plateau (Fig. 1), covering an area of >5 • 106 km, is an arid plateau with low relief and low erosion rates, and forms the largest area of high elevation (average elevation of 5023 m) and thick crust (65-80 km) on the planet (Fielding

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Section: Timescales Of Metamorphism Melting and Channel Flowmentioning

confidence: 99%

Section: Greater Himalayan Sequencementioning

confidence: 99%

Crustal structure, restoration and evolution of the Greater Himalaya in Nepal-South Tibet: implications for channel flow and ductile extrusion of the middle crust

2006

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“…The significant signature is the presence of the detrital zircon U-Pb age peak of ~544 Ma in the Paleozoic sedimentary rocks from the Baoshan, Tengchong blocks and TethyanHimalaya belt ( Fig. 7e; Dong et al, 2013;Gehrels et al, 2006;Godin et al, 2001;DeCelles, 2000;DeCelles et al, 1998). These Cambrian-Ordovician detrital zircons are also observed in the Pan-African orogenic belts associated with the formation of the Gondwana supercontinent (Wang et al, 2012;Xu et al, 2012).…”

Section: Provenance and Tectonic Implicationsmentioning

confidence: 99%

Detrital zircon U-Pb geochronology and Lu-Hf isotopic compositions of the Wuliangshan metasediment rocks in SW Yunnan (China) and its provenance implications

Xing

Wang

Zhang³

2016

J. Earth Sci.

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The Wuliangshan Group occurs to the east of the Lancang giant igneous zone in SW Yunnan, and is mainly composed of low-grade metamorphosed sedimentary rocks. The group has been considered as the syn-orogenic product of the Baoshan with Simao-Indochina blocks. However, its depositional time and provenance remain to be poorly constrained. This paper presents zircon U-Pb dating and Lu-Hf-isotopic data for five representative sandstone samples from the Wuliangshan Group. The detrital grains yield a major age-peak at ~259 Ma, and four subordinary age-peaks at ~1 859, ~941, ~788, and ~447 Ma, respectively. Our results suggest that the Wuliangshan metasedimentary sequence was deposited after Middle Triassic rather than previously-thought Cambrian. The detrital zircon age spectrum, along with in-situ Lu-Hf isotopic data suggest that the Wuliangshan Group might be a syncollisional sedimentary product related to the collision of Baoshan with Simao-Indochina blocks. It is inferred that the provenance of the Wuliangshan Group is mainly from the Simao/Yangtze blocks to the east rather than the Baoshan Block or Lancang igneous zone to the west. KEY WORDS: detrital zircon U-Pb dating, Lu-Hf isotopic composition, Wuliangshan sandstone sequence, Middle Triassic, Simao-Indochina. INTRODUCTIONThe SE Asia has been assembled by a series of collision and accretion processes involving numerous continental blocks or fragments separated from the East Gondwana since the Paleozoic (Faure et al., 2014;Metcalfe, 2006). The catchment areas of the Lancang, Jinsha and Nujiang rivers (also named Sanjiang in Chinese literature) in SW Yunnan (SW China) have preserved abundant paleotethyan heritages (e.g., the Lincang giant igneous zone) at which kilometer-thick Triassic volcanic rocks and Upper Triassic/Lower Jurassic molasse sediments are considered to have resulted from closure of the Paleotethys main ocean and subsequent continental collision (Peng et al., 2008(Peng et al., , 2006 Jian et al., 2003a, b;Mo et al., 1998;Zhong, 1998; Cong et al., 1993;Mahawat et al., 1990;Liu et al., 1989;Zhang et al., 1985).It has been commonly accepted that the Paleotethys main ocean was closed by an eastward subduction beneath the Indochina-Simao Block in the Permian-Triassic (Zaw et al., 2014;Wang et al., 2010). However, the precise timing of the initial collision of the Baoshan and Simao-Indochina blocks remains to be disputed. Previous studies focused on the origin of the Triassic igneous rocks along the Lancangjiang tectonic zone. Little attention has been paid to the coeval sedimentary rocks which preserved abundant geological records on the Paleotethyan tectonic evolution. The sedimentary rocks can provide key information to the time of closure of the Paleotethyan Ocean and subsequent collision of the Baoshan and Simao-Indochina blocks. The Wuliangshan Group occurs to the east of the Lancang giant igneous zone. It is mainly composed of low-grade metamorphosed sedimentary rocks. This group is likely syn-orogenic product of the Paleotethyan orog...

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“…In the central Himalaya, most leucogranite emplacement ages are Early-Middle Miocene (~24 to ~12 Ma) [4,9,12,29,31,36,37,69]; but some leucosome yield Oligocene ages [6,23].…”

Section: Timing Of Ductile Deformation Beneath the Ndmentioning

confidence: 99%

“…Normal faulting along the STDS has often been associated with magmatism within the Upper Himalaya Crystalline Sequence (UHCS). This magmatism took place from ~24 to ~12 Ma , with some evidence for an older magmatic activity since ~36 Ma [6,23,24]. In more detail the age range may result from different interpretations of the age populations within each sample, and of the structural relationships of the dated granite with respect to the deformation (pre, syn or post deformation).…”

mentioning

confidence: 99%

Ductile deformation within Upper Himalaya Crystalline Sequence and geological implications, in Nyalam area, Southern Tibet

Liu

Leloup

et al. 2012

Chin. Sci. Bull.

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The South Tibet Detachment System (STDS) is a flat normal fault that separates the Upper Himalaya Crystalline Sequence (UHCS) below from the Tethyan Sedimentary Sequence (TSS) above. Timing of deformations related to the STDS is critical to understand the mechanism and evolution of the Himalaya collision zone. The Nyalam detachment (ND) (~86°E) locates in the middle portion of STDS (81°-89°E). Dating of deformed leucocratic dykes that are most probably syntectonic at different depth beneath the ND, allow us to constrain the timing of deformation. (1) Dyke T11N37 located ~3500 m structurally below the ND emplaced at 27.4± 0.2 Ma; (2) Dyke T11N32 located ~1400 m structurally below the ND emplaced at 22.0±0.3 Ma; (3) T11N25 located within the top to the north STD shear zone, ~150 m structurally below the ND, emplaced at 17.1±0.2 Ma. Combining ND footwall cooling history and T11N25 deformation temperature, we indicate a probable onset of top to the north deformation at ~16 Ma at this location. These results show an upward younging of the probable timing of onset of the deformation at different structural distance below the ND. We then propose a new model for deformation migration below the ND with deformation starting by pure shear deformation at depth prior to ~27.5 Ma that migrates upward at a rate of ~ 0.3 mm/a until ~18 Ma when deformation switches to top to the north shearing in the South Tibet Detachment shear zone (STDsz). As deformation on the ND stops at 14-13 Ma this would imply that significant top to the North motion would be limited to less than 5 Ma and would jeopardize the importance of lower channel flow.

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Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and ⁴⁰Ar/³⁹Ar Thermochronology

Cited by 246 publications

References 65 publications

Crustal structure, restoration and evolution of the Greater Himalaya in Nepal-South Tibet: implications for channel flow and ductile extrusion of the middle crust

Crustal structure, restoration and evolution of the Greater Himalaya in Nepal-South Tibet: implications for channel flow and ductile extrusion of the middle crust

Detrital zircon U-Pb geochronology and Lu-Hf isotopic compositions of the Wuliangshan metasediment rocks in SW Yunnan (China) and its provenance implications

Ductile deformation within Upper Himalaya Crystalline Sequence and geological implications, in Nyalam area, Southern Tibet

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Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and 40Ar/39Ar Thermochronology

Cited by 246 publications

References 65 publications

Crustal structure, restoration and evolution of the Greater Himalaya in Nepal-South Tibet: implications for channel flow and ductile extrusion of the middle crust

Crustal structure, restoration and evolution of the Greater Himalaya in Nepal-South Tibet: implications for channel flow and ductile extrusion of the middle crust

Detrital zircon U-Pb geochronology and Lu-Hf isotopic compositions of the Wuliangshan metasediment rocks in SW Yunnan (China) and its provenance implications

Ductile deformation within Upper Himalaya Crystalline Sequence and geological implications, in Nyalam area, Southern Tibet

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Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and ⁴⁰Ar/³⁹Ar Thermochronology