Crustal shortening in convergent orogens: Insights from global positioning system (GPS) measurements in northeast India

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.Relative motion between converging plates results in stress accumulation within the plates as well as along their common boundary. The plates undergo rotational motion

Indian National GNSS Programme: Crustal deformation measurements in the Indian Sub-continent

“…The Karakoram fault is a very significant unit in the Himalayan tectonics and is considered to accommodate some motion across it. GPS observations indicate a slip rate of about 3 mm/yr (Mukul et al, 2010) which are consistent with the earlier estimates derived from geological data.…”

“…Sol et al (2007) stated that the change in rate and distribution of deformation across the easternmost Himalaya may be related to the geodynamics of the eastern Himalayan syntaxis and the rollback of the Indian slab beneath Burma. In a recent study, Mukul et al (2010) estimated that the convergence is being accommodated in the NE Himalayan wedge at a rate of about 15-20 mm/yr and approximately 1.5-3.5 mm/yr ($10-20%) of the present-day convergence in the NE Himalayan wedge is being accommodated in the Shillong Plateau.…”

Discriminatory characteristics of seismic gaps in Himalaya

“…Rajendran and Rajendran (2011) surmised that the last penultimate earthquake in the 1950 upper Assam sources may have occurred 500 years ago. Mukul et al (2010) estimated that the convergence is being accommodated in the NE Himalayan wedge at a rate of about 15-20 mm per year. The largest earthquake (1950, M w 8.4-8.6) occurred near syntaxial bend (Mukhopadhyay et al 2011a).…”

Estimation of present-day inter-seismic deformation in Kopili fault zone of north-east India using GPS measurements

“…Geologically, Shillong plateau comprises of rocks from the oldest Precambrian gneissic complex to the recent alluvium formations. Approximately, 1.5À3.5 mm/yr of the present-day total NÀS convergence in the eastern Himalaya is accommodated in Shillong plateau (Mukul et al 2010). The 1897 great Shillong earthquake (Ms 8.7) (Oldham 1899) occurred at western edge of the Shillong plateau.…”