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Using U-Th-Pb petrochronology to determine rates of ductile thrusting: time windows into the Main Central Thrust, Sikkim Himalaya

Mottram, Catherine M.; Parrish, Randall R.; Regis, Daniele; Warren, Clare J.; Argles, Tom W.; Harris, Nigel B. W. and Roberts, Nick M. W. (2015). Using U-Th-Pb petrochronology to determine rates of ductile thrusting: time windows into the Main Central Thrust, Sikkim Himalaya. Tectonics, 34(7) pp. 1355–1374.

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DOI (Digital Object Identifier) Link: https://doi.org/10.1002/2014TC003743
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Abstract

Quantitative constraints on the rates of tectonic processes underpin our understanding of the mechanisms that form mountains. In the Sikkim Himalaya, late structural doming has revealed time-transgressive evidence of metamorphism and thrusting that permit calculation of the minimum rate of movement on a major ductile fault zone, the Main Central Thrust (MCT), by a novel methodology. U-Th-Pb monazite ages, compositions, and metamorphic pressure-temperature determinations from rocks directly beneath the MCT reveal that samples from ~50 km along the transport direction of the thrust experienced similar prograde, peak, and retrograde metamorphic conditions at different times. In the southern, frontal edge of the thrust zone, the rocks were buried to conditions of ~550°C and 0.8 GPa between ~21 and 18 Ma along the prograde path. Peak metamorphic conditions of ~650°C and 0.8–1.0 GPa were subsequently reached as this footwall material was underplated to the hanging wall at ~17–14 Ma. This same process occurred at analogous metamorphic conditions between ~18–16 Ma and 14.5–13 Ma in the midsection of the thrust zone and between ~13 Ma and 12 Ma in the northern, rear edge of the thrust zone. Northward younging muscovite 40Ar/39Ar ages are consistently ~4 Ma younger than the youngest monazite ages for equivalent samples. By combining the geochronological data with the >50 km minimum distance separating samples along the transport axis, a minimum average thrusting rate of 10 ± 3 mm yr−1 can be calculated. This provides a minimum constraint on the amount of Miocene India-Asia convergence that was accommodated along the MCT.

Item Type: Journal Item
Copyright Holders: 2015 The Authors
ISSN: 0278-7407
Project Funding Details:
Funded Project NameProject IDFunding Body
Not SetNE/1528018/1NERC
Not SetNE/HO16279/1NERC
Not SetIP-1129-0511NERC
Not SetIJP 2008/R3Royal Society International Joint Project
Keywords: ductile thrusting; Himalaya; monazite geochronology; petrochronology
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 43785
Depositing User: Nigel Harris
Date Deposited: 23 Jul 2015 08:30
Last Modified: 09 Dec 2018 09:38
URI: http://oro.open.ac.uk/id/eprint/43785
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