Deformation in the diffuse India‐Capricorn‐Somalia triple junction from a multibeam and magnetic survey of the northern Central Indian ridge, 3°S–10°S

Abstract

We use new multibeam and magnetic observations from 3°S–10°S along the Central Indian ridge to describe morphotectonic features and spreading fabrics within the study area and quantify deformation across the diffuse India‐Capricorn‐Somalia triple junction. A megamullion adjacent to the Vityaz transform fault is the first reported for the northern Central Indian ridge. The principal transform displacement zone (PTDZ) of the Vema transform fault consists of several closely spaced faults that can be traced for more than 150 km. Serpentinite or volcanic intrusions that are offset by the Vema PDTZ have inferred ages of 30,000–45,000 years, testifying to the youth of active features on the valley floor. Abyssal hill orientations throughout the study area have remained constant since at least 4 Ma, implying little or no change in the opening direction during this period. Abyssal hills from opposite sides of the ridge have the same orientations within our 1°–3° errors, implying that slip along reactivated fracture zones in the diffuse triple junction neither significantly rotates nor shears the intervening seafloor. Transform fault azimuths in the survey area agree with the NUVEL‐1 Africa‐Australia slip direction but are 5°–9° clockwise from the Africa‐India direction. In contrast, seafloor spreading rates in the study area agree better with the NUVEL‐1 Africa‐India predictions. These seemingly conflicting observations are reconciled by a model in which seafloor within the diffuse triple junction rotates about the India‐Capricorn pole at angular rotation rates that increase monotonically from zero to the full rotation rate across the deforming zone.