Himalayan Collision Tectonics

Abstract

The evolutionary nature of the area encompassing Cuddapah basin, Nellore Schist Belt and the Ongole domain of Eastern Ghats Belt (south India), which contains Paleo-Neoproterozoic imprints of thick sedimentation, intense magmatism, subduction/accretion and possible collision between eastern Dharwar craton and east Antarctica, is still being debated. An attempt has been made here to decipher the deep crustal structure and tectonics of this region, by reprocessing Deep Seismic Sounding data acquired earlier through the modeling of first arrival refraction and wide angle reflection travel times. The derived crustal seismic velocity structure reveals that the intracratonic Proterozoic Cuddapah basin containing only 4 km thick sediment is bounded by two major faults. The Moho reaching fault detected on its eastern boundary, demarcates Cuddapah basin from the Nellore Schist Belt. Although a deep normal fault is mapped within the Nallamalai Fold Belt, but no thrusting signatures are apparent. Almost all the crustal layers beneath Nellore Schist Belt and the Ongole domain of Eastern Ghats Belt, show distinct eastward dipping trend conforming to an upthrusted feature, suggesting possible presence of a collisional suture. Besides, the areas lying east of Cuddapah Basin appear to be an accreted orogenic terrain, beneath which lower crust has upwarped substantially. The entire stretch of the studied region is underplated by unprecedently thick (∼20 km) high velocity (7.0-7.4 km/s) magma layer above the Moho, indicating strong crust-mantle thermal perturbation and massive subcrustal erosion. Further, an expression of a deep seated mantle thermal anomaly has also been found below the Parnapalle region of the SW Cuddapah basin beneath which deeper crustal layers have exhumed.