Metamorphic zonation, migmatization and leucogranites along the Everest transect of Eastern Nepal and Tibet: record of an exhumation history

Pognante, Ugo; Benna, Piera

doi:10.1144/gsl.sp.1993.074.01.22

Cited by 71 publications

(80 citation statements)

References 34 publications

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“…Thus, the Lower Paleozoic metamorphism during the Pan African orogeny seems to be nearly as strong as the Tertiary Himalayan orogeny to produce anatectic melts generating granites and migmatites. This interpretation confirms with the similar conclusions made by Gehrels et al (2006a,b) for the Kathmandu and Dadeldhura thrust sheets in central and far western Nepal and Tonarini et al (1994) and Pognante and Benna, (1993) for Everest-Makalu region. The high U/Th ratio ( (Yoshida and others, 2007, 2008a;Yoshida and Upadhyay, 2009).…”

Section: Acknowledgementssupporting

confidence: 91%

Proceedings of the 25th Himalaya-Karakoram-Tibet Workshop

Leech¹,

Klemperer²,

Mooney³

2010

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Section: Acknowledgementssupporting

confidence: 91%

Proceedings of the 25th Himalaya-Karakoram-Tibet Workshop

Leech¹,

Klemperer²,

Mooney³

2010

Open-File Report

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“…In the transect from the Arun valley, W of Num, to Makalu through the Barun valley (Brunel and Kienast, 1986;Pognante and Benna, 1993;Goscombe and Hand, 2000), the MCTZ is a complex sequence of Barrovian metamorphic rocks bounded at the top by a belt of thrust sheets (Bordet, 1961;Lombardo et al, 1993) (Fig. 1c) that are roughly coincident with the HHT as defined by Goscombe et al (2006).…”

Section: The Arun-makalu Transectmentioning

confidence: 99%

Early Oligocene partial melting in the Main Central Thrust Zone (Arun valley, eastern Nepal Himalaya)

Groppo

Rubatto

Rolfo

et al. 2010

Lithos

113

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The Main Central Thrust Zone (MCTZ) is a key tectonic feature in the architecture of the Himalayan chain. In the Arun valley of the eastern Nepal Himalaya, the MCTZ is a strongly deformed package of amphibolite-to granulite facies metapelitic schist and granitic orthogneiss. This package is tectonically interposed between the underlying, low-grade, Lesser Himalaya sequences and the overlying, high-grade and locally anatectic, Higher Himalayan Crystallines (HHC). The MCTZ is characterized by a well documented inverted metamorphism from the Grt-Bt zone, across the Ky-in, St-in and -out, Kfs-in, Ms-out and Sil-in isograds. Partial melting with local occurrence of migmatitic segregations has been rarely reported from the highest structural levels of the MCTZ. While it is widely accepted that thrusting along the MCT occurred during the Miocene, geochronological data constraining the timing of crustal anatexis in the upper portion of the MCTZ are still lacking. In order to understand the link between partial melting in the MCTZ and the Miocene activation of the MCT, we present the P-T-time evolution of a kyanite-bearing anatectic gneiss occurring at the highest structural levels of the MCTZ, along the Arun-Makalu transect (Eastern Nepal). Microstructural observations combined with P-T pseudosection analysis show that dehydration partial melting occurred in the kyanite-field. After reaching peak conditions at about 820°C, 13 kbar, the studied sample experienced decompression accompanied by cooling down to 805°C, 10 kbar, which caused in situ melt crystallization. SHRIMP monazite and zircon geochronology provides evidence that the anatexis affecting the upper portion of the MCTZ occurred during Early Oligocene (~31 Ma). These results demonstrate that in the upper MCTZ, at least in the eastern Himalaya, crustal anatexis was earlier than, and not a consequence of, decompression linked to exhumation along the MCT.2

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“…The restoration shows the position of the two major low-angle normal faults that cut through Everest itself: the upper Qomolangma detachment which flattens out along the top of the Ordovician 'Yellow Band'; and the lower Lhotse detachment, which bounds most of the large leucogranite sills (Searle 1999a, b;. The Everest granites must have been sourced within the Proterozoic black shales that formed the protolith of the sillimanite gneisses comprising Unit 1 in the GHS, also called the Barun gneiss (Pognante & Benna 1993;Lombardo et al 1993). We discard the previous 'stratigraphic' nomenclature of the GHS (e.g.…”

Section: Crustal Structure Of the Everest Transectmentioning

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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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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Metamorphic zonation, migmatization and leucogranites along the Everest transect of Eastern Nepal and Tibet: record of an exhumation history

Cited by 71 publications

References 34 publications

Proceedings of the 25th Himalaya-Karakoram-Tibet Workshop

Proceedings of the 25th Himalaya-Karakoram-Tibet Workshop

Early Oligocene partial melting in the Main Central Thrust Zone (Arun valley, eastern Nepal Himalaya)

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

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