Abstract
SUMMARY Analysis of 3100 km of newly acquired marine magnetic data constrained by satellite and shipborne free air gravity anomalies in the corridor between the 86°E fracture zone and Ninetyeast Ridge, north of the equator reveals the evolutionary history of the Late Cretaceous crust characterised by anomaly 34 through 31 (83.5-68.7 Ma) under complex tectonic settings. Seafloor spreading model studies suggest that the crust, particularly between the chrons 33R and 33 (79.0 - 73.6 Ma) was formed with variable and slightly higher half-spreading rates (4.8 - 7.1 cm/yr) than the crust of similar age either in the regions west of 86°E fracture zone, east of the Ninetyeast Ridge or the Southern Crozet Basin. Further, the interpretation of magnetic anomalies suggests the presence of fossil spreading ridge segments and extra oceanic crust on the Indian plate that has been transferred from the Antarctica plate by discrete southward ridge jumps. These ridge jumps are caused by thermal instability of the spreading center as the Indian plate moved northward over the Kerguelen mantle plume. The present study indicates that the spreading ridge-plume interaction is the prime mechanism for these ridge jumps, which have occurred since 75.8 Ma. The newly identified magnetic anomalies 34 through 31 and the inferred ~N3°E trending fracture zones refined the plate reconstruction models for that period.
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