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.

DOI: https://doi.org/10.1002/2014TC003743

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.

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About

• Item ORO ID
• 43785
• Item Type
• Journal Item
• ISSN
• 0278-7407
• Project Funding Details

• Funded Project Name	Project ID	Funding Body
  Not Set	NE/1528018/1	NERC
  Not Set	NE/HO16279/1	NERC
  Not Set	IP-1129-0511	NERC
  Not Set	IJP 2008/R3	Royal Society International Joint Project

• Keywords
• ductile thrusting; Himalaya; monazite geochronology; petrochronology
• Academic Unit or School
• Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
  Faculty of Science, Technology, Engineering and Mathematics (STEM)
• Copyright Holders
• © 2015 The Authors
• Depositing User
• Nigel Harris