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Thermal metamorphism of the Arunachal Himalaya, India: Raman thermometry and thermochronological constraints on the tectono-thermal evolution

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Title Thermal metamorphism of the Arunachal Himalaya, India: Raman thermometry and thermochronological constraints on the tectono-thermal evolution
 
Creator MATHEW, G
DE SARKAR, S
PANDE, K
DUTTA, S
ALI, S
RAI, A
NETRAWALI, S
 
Subject RSCM
Inverted metamorphism
Geothermometer
Himalaya
Thermochronology
Channel flow
MAIN CENTRAL THRUST
CRUSTAL CHANNEL FLOWS
INVERTED METAMORPHISM
CARBONACEOUS-MATERIAL
CENTRAL NEPAL
ACCRETIONARY WEDGES
LESSER HIMALAYA
THERMOBAROMETRIC CONSTRAINTS
EXHUMATION HISTORY
SIKKIM HIMALAYAS
 
Description Determination of the peak thermal condition is vital in order to understand tectono-thermal evolution of the Himalayan belt. The Lesser Himalayan Sequence (LHS) in the Western Arunachal Pradesh, being rich in carbonaceous material (CM), facilitates the determination of peak metamorphic temperature based on Raman spectroscopy of carbonaceous material (RSCM). In this study, we have used RSCM method of Beyssac et al. (J Metamorph Geol 20:859-871, 2002a) and Rahl et al. (Earth Planet Sci Lett 240:339-354, 2005) to estimate the thermal history of LHS and Siwalik foreland from the western Arunachal Pradesh. The study indicates that the temperature of 700-800 A degrees C in the Greater Himalayan Sequence (GHS) decreases to 650-700 A degrees C in the main central thrust zone (MCTZ) and decreases further to < 200 A degrees C in the Mio-Pliocene sequence of Siwaliks. The work demonstrates greater reliability of Rahl et al.'s (Earth Planet Sci Lett 240:339-354, 2005) RSCM method for temperatures > 600 and < 340 A degrees C. We show that the higher and lower zones of Bomdila Gneiss (BG) experienced temperature of similar to 600 A degrees C and exhumed at different stages along the Bomdila Thrust (BT) and Upper Main Boundary Thrust (U.MBT). Pyrolysis analysis of the CM together with the Fission Track ages from upper Siwaliks corroborates the RSCM thermometry estimate of similar to 240 A degrees C. The results indicate that the Permian sequence north of Lower MBT was deposited at greater depths (> 12 km) than the upper Siwalik sediments to its south at depths < 8 km before they were exhumed. The Ar-40/Ar-39 ages suggest that the upper zones of Se La evolved similar to 13-15 Ma. The middle zone exhumed at similar to 11 Ma and lower zone close to similar to 8 Ma indicating erosional unroofing of the MCT sheet. The footwall of MCTZ cooled between 6 and 8 Ma. Analyses of P-T path imply that LHS between MCT and U.MBT zone falls within the kyanite stability field with near isobaric condition. At higher structural level, the temperatures increase gradually with P-T conditions in the sillimanite stability field. The near isothermal (700-800 A degrees C) condition in the GHS, isobaric condition in the MCTZ together with T-t path evidence of GHS that experienced relatively longer duration of near peak temperatures and rapid cooling towards MCTZ, compares the evolution of GHS and inverted metamorphic gradient closely to channel flow predictions.
 
Publisher SPRINGER
 
Date 2014-10-15T16:01:59Z
2014-10-15T16:01:59Z
2013
 
Type Article
 
Identifier INTERNATIONAL JOURNAL OF EARTH SCIENCES, 102(7)1911-1936
http://dx.doi.org/10.1007/s00531-013-0904-6
http://dspace.library.iitb.ac.in/jspui/handle/100/15220
 
Language en