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

作者：Warren Clare J^*; Singh Athokpam K; Roberts Nick M W; Regis Daniele; Halton Alison M; Singh Rajkumar B

来源：Lithos, 2014, 200: 94-110.

DOI：10.1016/j.lithos.2014.04.005

• Himalaya
• Arunachal Pradesh
• Zimithang Thrust
• Ar-40/Ar-39
• U-Pb
• Monazite

The Zimithang Thrust juxtaposes two lithotectonic units of the Greater Himalayan Sequence in Arunachal Pradesh, NE India. Monazite U-Pb, muscovite Ar-40/Ar-39 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 +/- 03 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 (similar to 525-650 degrees C). Elevated temperatures of similar to 700 degrees C appear to have been reached in the high strain zone itself and in the footwall further from the thrust. Single grain fusion Ar-40/Ar-39 muscovite data from samples either side of the thrust yield ages of similar to 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 orogenparallel out-of-sequence structures disrupt the Greater Himalayan Sequence at different times during Himalayan evolution, and highlight an eastwards-younging trend in Ar-40/Ar-39 muscovite cooling ages at equivalent structural levels along Himalayan strike.

• 出版日期2014-7