Structure and Geological Processes of the Earth: Seismic Evidences from the Indian Shield

Abstract

The Earth is a dynamic planet with a large number of geological processes taking place inside it. The internal processes lift and build the Earth’s surface, whereas the external processes tend to destroy the shape of the Earth’s relief by weathering, erosion and hydrological cycle. The paper places the crustal structure of the Indian shield in the context of global processes and evolution of the Earth. It summarizes internal structure of the Earth from core to crust and addresses numerous geological processes, like evolution of continental crust, operation of plate tectonics, convection currents, mantle plumes and supercontinental episodes using seismic and seismological images. Seismic images provide key evidences of the geological processes that are being taking place inside the Earth. Seismic images from the Archean and Proterozoic terrains of the Indian shield show evidence for operation of plate tectonics since Neoarchean. Further, they suggest differences in mode of subduction process during these periods. They provide evidences for the associated processes, like delamination, asthenospheric upwelling, and generation of younger Moho due to crust-mantle interaction. Evolution of sedimentary basins, passive continental margins, the Deccan Volcanic Province, Rajmahal traps and magmatic underplating are interpreted in terms of mantle plume activities using seismic images. Seismological data from Burmese arc region suggest an overturn of subducted Indian lithospheric slab at the transition zone (410–660 km depth) and its slow sinking leading to detachment. Further, remnants of detached lithospheric slabs from the Himalayan-Alps orogenic system are observed at various mantle depths ranging between 1000 and 2300 km beneath the Indian shield. Such displaced slab material pushes the other material to rise somewhere and thereby generate plumes/super plumes. These plumes break the supercontinent, which in turn cause plate movements on the surface. Tomographic studies suggest whole-mantle convection and provide key evidences for the mantle processes. The role of both the internal and external geological processes that shape the Earth are explained from the evolution of Himalayas and generation of huge sediments from it with the formation of world’s largest Bengal fan.