Timing and conditions of peak metamorphism and cooling across the Zimithang Thrust, Arunachal Pradesh, India

Warren, Clare J.; Singh, Athokpam K.; Roberts, Nick M.W.; Regis, Daniel; Halton, Alison M. and Singh, Rajkumar B. (2014). Timing and conditions of peak metamorphism and cooling across the Zimithang Thrust, Arunachal Pradesh, India. Lithos, 200-201 pp. 94–110.

DOI: https://doi.org/10.1016/j.lithos.2014.04.005

Abstract

The Zimithang Thrust juxtaposes two lithotectonic units of the Greater Himalayan Sequence in Arunachal Pradesh, NE India. Monazite U–Pb, muscovite ⁴⁰Ar/³⁹Ar and thermobarometric data from rocks in the hanging and footwall constrain the timing and conditions of their juxtaposition across the structure, and their subsequent cooling. Monazite grains in biotite–sillimanite gneiss in the hanging wall yield LA-ICP-MS U–Pb ages of 16 ± 0.2 to 12.7 ± 0.4 Ma. A schistose gneiss within the high strain zone yields overlapping-to-younger monazite ages of 14.9 ± 0.3 to 11.5 ± 0.3 Ma. Garnet–staurolite–mica schists in the immediate footwall yield older monazite ages of 27.3 ± 0.6 to 17.1 ± 0.2 Ma. Temperature estimates from Ti-in-biotite and garnet–biotite thermometry suggest similar peak temperatures were achieved in the hanging and footwalls (~ 525–650 °C). Elevated temperatures of ~ 700 °C appear to have been reached in the high strain zone itself and in the footwall further from the thrust. Single grain fusion ⁴⁰Ar/³⁹Ar muscovite data from samples either side of the thrust yield ages of ~ 7 Ma, suggesting that movement along the thrust juxtaposed the two units by the time the closure temperature of Ar diffusion in muscovite had been reached. These data confirm previous suggestions that major orogen-parallel out-of-sequence structures disrupt the Greater Himalayan Sequence at different times during Himalayan evolution, and highlight an eastwards-younging trend in ⁴⁰Ar/³⁹Ar muscovite cooling ages at equivalent structural levels along Himalayan strike.

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About

• Item ORO ID
• 40186
• Item Type
• Journal Item
• ISSN
• 0024-4937
• Project Funding Details

• Funded Project Name	Project ID	Funding Body
  From subduction to sand: Quantifying the balance between tectonic and surface processes during early continental collision and UHP rock exhumation	NE/H016279/1	NERC (Natural Environment Research Council)
  Not Set	IP-1270-1111	NIGFSC

• Keywords
• Himalaya; Arunachal Pradesh; Zimithang Thrust; 40Ar/39Ar; U–Pb; monazite
• 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
• © 2014 The Authors
• Depositing User
• Clare Warren