Crustal shortening in convergent orogens: Insights from global positioning system (GPS) measurements in northeast India |
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Authors: | Malay Mukul Sridevi Jade Anjan Kumar Bhattacharyya and Kuntala Bhusan |
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Abstract: | Deformation in active mountain belts like the Himalaya is manifested over several spatial and temporal scales and collation
of information across these scales is crucial to an integrated understanding of the overall deformation process in mountain
belts. Computation and integration of geological shortening rates from retrodeformable balanced cross-sections and present-day
convergent rates from deforming mountain belts is one way of integrating information across time-scales. The results from
GPS measurements carried out in NE India indicate that about 15–20 mm/yr of convergence is being accommodated there. Balanced-cross
sections from the NE Himalaya indicate about 350–500 km of shortening south of the South Tibet Detachment (STD). Geothermobarometry
suggest that the rocks south of the STD deformed under peak metamorphic conditions at ∼ 22 Ma. This indicates a geological
convergence rate of ∼ 16–22 mm/yr which appears to be fairly consistent with the GPS derived convergence rates. Approximately
1.5 to 3.5 mm/yr (∼ 10–20 %) of the total N-S of the present-day convergence in the NE Himalaya is accommodated in the Shillong
Plateau. In addition, ∼ 8–9 mm/yr of E-W convergence is observed in the eastern and central parts of the Shillong Plateau
relative to the Indo-Burman fold-thrust belt. Balanced cross-sections in the Indo-Burman wedge together with higher resolution
GPS measurements are required in the future to build on the first-order results presented here. |
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