Tectonics of the Ninetyeast Ridge derived from the spreading records of the contiguous oceanic basins and age constraints of the ridge

A major scientific expedition in the Indian Ocean was accomplished onboard RV Roger Revelle (KNOX06RR) to investigate the evolution of the Ninetyeast Ridge and to understand the spreading activity particularly in close proximity to the Kerguelen hotspot. Comparison of the magnetic anomaly data of both the Central Indian and Wharton basins with synthetic profiles reveals magnetic lineations 19 through 34, several near N-S oriented fracture zones, and fossil ridge segments ceased at 65 and 42 Ma. The trends of fracture zones (~N5°E) and Ninetyeast Ridge (~N10°E) are in obliquity. Thus the 89°E FZ in the south borders the Ninetyeast Ridge on east side, while in the north the same FZ borders the ridge on west side and led to largely control the morphology of the ridge. The magnetic pattern of the region disclose that the oceanic crust close to the Ninetyeast Ridge, particularly between 86°E FZ and 90°E FZ shows highly diachronic age succession together with fossil ridge segments of discrete ages (65 and 42 Ma). In addition, stretches of the Ninetyeast Ridge and oceanic crust in adjacent basins evolved during the contemporaneous ages between 77 and 43 Ma suggest that the ridge was accreted at a rate of almost a factor-of-two acceleration (~118 km/Myr) in comparison to that of the oceanic crust formation (50 - 58 km/Myr). The proximity of spreading activity and the Kerguelen hotspot volcanism was continually in dynamic state due to the absolute motion of the Indian plate toward north and hotspot drift in SSW direction. During the emplacement of the Ninetyeast Ridge, the spreading centers and the Kerguelen hotspot have gradually come closer and then underwent for ridge jumps in order to keep ridge-segments away from the hotspot.