Strain localization, granulite formation and geodynamic setting of hot orogens': a case study from the Eastern Ghats Province, India

The Eastern Ghats Province underwent major orogenic events in the NeoproterozoicCambrian period: 980930, 900650 and 550500?Ma. At each time interval, deformation occurred synchronous with high-grade metamorphism. The first event was characterized by distributed strain throughout the entire province, while strain and thermal anomalies during the later orogenies were confined to the province boundaries. In the first case, pre-orogenic rifting caused ultrahigh-temperature metamorphism at the base of the crust, and was closely followed by crustal shortening related to the collision of the granulite belt with the Indian craton. The thermal anomaly persisting from the rifting event, followed by the thermal relaxation associated with crustal shortening led to prolific melt production and transfer of heat producing elements (HPE) into the middle and upper parts of the thick post-collisional crust. Heating and associated melting caused rheological weakening of the crustal section, and explains why strain was distributed across the entire thermally perturbed zone. Erosion removed a substantial portion of the HPE-rich upper crust, and deposited the detritus in cratonic sedimentary basins to the west. Subsequently, the rheologically stronger Eastern Ghats Province crust could effectively transmit stresses and concentrate them along pre-existing zones of weakness near the province boundaries. Progressive thrusting in these domains led to consistent loading of the footwall, even as it underwent thermal relaxation. Since both strain and heating were associated with the footwall of pre-existing discontinuities, the hot orogen so formed was also spatially restricted. Copyright (c) 2011 John Wiley & Sons, Ltd.