Geophysical evidence for late stage magmatism at the central Ninetyeast Ridge, Eastern Indian Ocean

The Ninetyeast Ridge is a well-studied hot spot trail in the Indian Ocean. A recent geophysical survey in its central portion near 17 degrees S includ ed Hydrosweep bathymetric mapping, Parasound echosounder profiles, and high resolution seismic reflection data. These data reveal a number of small co nes of a few hundreds of meters in diameter and up to 200 m height. Seismic evidence exists regarding a magmatic origin of these features. Different e vents of basaltic flow and tuff deposition intercalated with hemipelagic oo zes of Eocene to present age, as being known from nearby drilling, allow da ting of these latest stages of volcanic activity. An activity of at least 6 Ma longer than termination of the dominant constructional phase of the rid ge can be demonstrated. These eruptions occur at shallow water depth, and s eem to be related to tectonic lineaments in the area. Transtensional stress es together with a more durable magmatic source beneath this part of the ri dge allow magma to ascend along pull-apart structures. The age discrepancy found calls for special attention when trying to reconstruct global plate m otions.