ISOSTATIC RESPONSE OF THE CENTRAL INDIAN RIDGE (WESTERN INDIAN-OCEAN)BASED ON TRANSFER-FUNCTION ANALYSIS OF GRAVITY AND BATHYMETRY DATA

The Central Indian Ridge (CIR) is a part of the major active mid-ocean ridge system trending north-south between 2 degrees N and the triple junction at 25 degrees S. Previous investigations suggest that the hal f-spreading rate varies from 1.6 to 2.5 cm/yr between the northern aci d southern ends of the ridge, and the diffuse plate boundary dividing the Indian and Australian plates intersects the Central Indian Ridge n ear 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 p rofiles, four in northern part of the ridge within or close to the dif fuse boundary zone, and six in southern part outside the zone have bee n utilized separately to obtain their isostatic response based on tran sfer function analysis. The admittance estimates for the long waveleng ths suggest that the elastic plate model fits the data for the compens ation of sea floor topography near the ridge crest. An effective elast ic 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 Rid ge, and a value from 10 to 17 km with an average T-e of 13 +/- 3 km fi ts the data for the southern part of the ridge. Isostatic response fun ction estimates confirm that the difference in elastic plate thickness es between the northern and southern segments is real and significant. The observed low effective elastic thickness for the data in the nort hern part of the Central Indian Ridge close to the diffuse boundary zo ne is interpreted as due to higher than average temperatures beneath t he ridge. These higher temperatures have been inferred due to the pert urbations of the regional heat flow anomaly associated with the diffus e plate boundary.