Large fault fabric of the Ninetyeast Ridge implies near-spreading ridge formation



[1] Ninetyeast Ridge (NER) is a linear volcanic ridge in the Indian Ocean thought to have formed by hotspot volcanism on the northward-drifting Indian plate. Geological data from the ridge are sparse, so its tectonic evolution is poorly known. We studied satellite-derived gravity data, seismic reflection profiles, and multibeam bathymetry to examine NER structure. Gravity data show that the ridge displays a series of nearly E-W trending lineations with average spacing ∼0.4° (45 km). In seismic and bathymetry data, these lineations correlate with horsts and grabens that probably formed near the time of ridge emplacement. From their extensional nature and trends, we infer that these faulted structures formed near the spreading ridge that separated the Indian and Antarctic plates and their ubiquity implies the hotspot was never far from this spreading ridge.