Isostatic response of the Central Indian Ridge (Western Indian Ocean) based on transfer function analysis of gravity and bathymetry data

Abstract

The Central Indian Ridge (CIR) is a part of the major active mid-ocean ridge system trending north-south between 2°N and the triple junction at 25°S. Previous investigations suggest that the half-spreading rate varies from 1.6 to 2.5 cm/yr between the northern and southern ends of the ridge, and the diffuse plate boundary dividing the Indian and Australian plates intersects the Central Indian Ridge near the equator. In the present study, I have attempted to investigate the nature of isostatic response of young oceanic topography created by spreading along the Central Indian Ridge. Gravity and bathymetric profiles, four in northern part of the ridge within or close to the diffuse boundary zone, and six in southern part outside the zone have been utilized separately to obtain their isostatic response based on transfer function analysis. The admittance estimates for the long wavelengths suggest that the elastic plate model fits the data for the compensation of sea floor topography near the ridge crest. An effective elastic thickness ranging from 5 to 10 km with an average T e of 7 ± 2 km fits best to the data for the northern part of the Central Indian Ridge, and a value from 10 to 17 km with an average T e of 13 ± 3 km fits the data for the southern part of the ridge. Isostatic response function estimates confirm that the difference in elastic plate thicknesses between the northern and southern segments is real and significant. The observed low effective elastic thickness for the data in the northern part of the Central Indian Ridge close to the diffuse boundary zone is interpreted as due to higher than average temperatures beneath the ridge. These higher temperatures have been inferred due to the perturbations of the regional heat flow anomaly associated with the diffuse plate boundary.