Two Decades of Indian Research on Ninetyeast Ridge Reveal how Seafloor Spreading and Mantle Plume Activities have Shaped the Eastern Indian Ocean

Abstract

on the northward-drifting Indian plate between ~85 and 42 Ma. The ridge is also unique because the feature is located within a diffuse deformation zone between three sub-plates, Indian, Australian and Capricorn and is associated with seismicity. The presence of the Ninetyeast Ridge in the Indian Ocean was first reported by Th. Stocks in 1960. Subsequently a comprehensive picture of the ocean floor emerged from the compilation of depth soundings made during the International Indian Ocean Expedition (1960–65), which emphasized the presence of this long, linear, aseismic ridge in the Indian Ocean. Emergence of plate tectonics and mantle plume hypotheses in the early 1960s led the way to mount rigorous experiments on the Ninetyeast Ridge for understanding its origin. The results of Legs 22 and 26 of the Deep Sea Drilling Project (DSDP) (1974), Leg 121 of the Ocean Drilling Program (ODP) (1989) and the geophysical surveys have helped establish that the Ninetyeast Ridge originated from the Kerguelen hot spot, when the volcanic source was located beneath the northward-moving Indian plate from the Late Cretaceous to the Early Cenozoic period. In the early 1990s, two bilateral programmes, viz. Trans Indian Ocean Geotraverse (TIOG) and Integrated Long-Term Programme (ILTP), aimed to understand better the evolution of the Indian Ocean lithosphere, were initiated with the support of the Indian and Russian governments. Subsequently in 2007, India participated in an International Expedition on the Ninetyeast Ridge for collection of bathymetry, magnetic and seismic reflection data together with basement samples from 33 sites along the ridge to investigate the behaviour of the Kerguelen hot spot during the formation of the ridge. From the Indian side, CSIR-National Institute of Oceanography (CSIR-NIO), Goa took a lead position in understanding the evolution, internal structure and several fundamental