Morphotectonics of the Carlsberg Ridge between 62 degrees 20 minutes and 66 degrees 20 minutes E, northwest Indian Ocean

Abstract

The segmentation pattern of 440 km long section of the Carlsberg Ridge between 62 degrees 20 minutes E and 66 degrees 20 minutes E, in the northwest Indian Ocean, has been studied using multibeam bathymetry and magnetic data. A well-defined transform fault is the only first order discontinuity documented in this section of the ridge. Four segments have been identified based on the topographic fabric, along-axis depth variations and the presence of off-axis traces of transform and non-transform discontinuities. These segments constitute four distinct domains representing magmatic and sparsely magmatic crustal accretion. Magnetic model studies show this section of the ridge is a slow spreading ridge with spreading half rates varying from 11 to 16 mm/yr. Along-axis variations in the magnetic anomalies and crustal magnetization, the presence of axial volcanic ridges on the inner valley floor, variations in the depth and geometry of the rift valley, and recovery of mantle derived peridotites from the inner valley floor suggest distinct variations in the accretionary processes along the ridge. It is suggested that the linear section in the east with ridge-parallel topographic fabric, continuous magnetic lineations, and the segment with a shallow valley floor with along-axis ridge propagation fabric, represent a magmatic phase of crustal accretion. The wide rift valley, recovery of mantle rocks, deformed topographic fabric, along-axis depth maxima and discontinuous magnetic lineations documented along the middle part of the ridge and the existence of short ridges east of the transform fault represent sparsely magmatic sections with dominance of tectonic extension.