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Rapid denudation of Higher Himalaya during late Pliestocence, evidence from OSL thermochronololgy

De Sarkar S., Mathew G., Pande K., Chauhan N., Singhvi A. K.

Geochronometria

2013

Vol. 40, no. 4

304--310

Optically Stimulated Luminescence (OSL) of quartz, with closure temperatures of 30-35°C in conjunction with Apatite Fission Track (AFT; closure temp. ~120°C) and 40Ar-39Ar (biotite closure temperature ~350°C), were used to obtain cooling ages from Higher Himalayan crystalline rocks of Western Arunachal Himalaya (WAH). Cooling age data based on OSL, AFT and Ar-Ar thermochro-nology provide inference on the exhumation – erosion history for three different time intervals over million to thousand year scale. Steady-state exhumation of ~0.5 mm/yr was observed during Miocene (>7.2 Ma) till Early Pleisto-cene (1.8 Ma). Onset of Pleistocene glacial/interglacial conditions from ~1.8 Ma formed glaciated valleys and rapid erosion with rivers incising deep valleys along their course. Erosion enables mid-crustal partial melts to move beneath the weak zone in the valley and causes an erosion-induced tec-tonic uplift. This resulted in a rapid increase in exhumation rate. The OSL thermochronology results suggest increased erosion over ~21 ka period from Late Pleistocene (2.5 mm/yr) to Early Holocene (5.5 mm/yr) and these are to be contrasted with pre 1.8 Ma erosion rate of 0.5 mm/yr. Enhanced ero-sion in the later stage coincides with the periods of de-glaciation during Marine Isotope Stages (MIS) 1 and 2. The results of the present study suggest that in the present setting OSL thermochronology in-formed on the short-term climatic effect on landscape evolution and techniques like the AFT and 40Ar-39Ar provided longer-term exhumation histories.