Segmentation and morphology of the Central Indian Ridge between 3°S and 11°S, Indian Ocean

Abstract

The segmentation pattern of 750 km long Central Indian Ridge (CIR) between 3 degrees S and 11 degrees S latitudes in the Indian Ocean has been studied using multibeam bathymetry and magnetic data. Twelve ridge segments were identified that are separated by well defined transform faults and non-transform discontinuities. Magnetic model studies qualify the ridge as a slow spreading ridge with average full spreading rates varying from 26 to 38 mm/yr. The disposition of the magnetic anomalies suggests that the plate opening direction has not changed during the last 0-4 Ma period. Along axis variations in the magnetic anomalies, presence of axial volcanic ridges on the inner valley floor, variations in the depth and geometry of the rift valley, suggest distinct variati'ons in the accretionary processes along the ridge. Based on these characteristics and the segmentation pattern, we suggest that ten ridge segments are undergoing less magmatic phase of extension, while two segments have shown characteristics of magmatic accretion. The linear segments with narrow and shallow rift valley floor and near symmetric magnetic anomalies are identified as segments with magmatic accretion. The influence of diffuse plate boundary zone on the young seafloor fabric generated by the CIR has been examined. The seafloor topography different from the normal ridge parallel fabric observed at few places over the NE flank of the CIR is suggested to be the consequence of gradual and progressive influence of the distributed diffuse plate boundary (between the Indian-Capricorn plates), on the newly generated oceanic lithosphere. Further, we documented distinct ridge-transform intersection (RTI) highs, three of these RTI highs are identified as oceanic core complexes/megamullion structures. Megamullion structures are found to be associated with less magmatic sections. Increased seismicity has been observed at the less magmatic segment ends suggesting the predominance of tectonic extension prevalent at the sparsely magmatic sections.