An analysis of the morphology and volcano-tectonic structure of the Central Indian Ridge between 18º and 21ºS

Abstract

The Central Indian Ridge (CIR) between 18° and 21°S shows significant morphological variation at a relatively constant spreading rate (between 47 and 51mmyr-1). High resolution TOBI sidescan sonar data (cruise CD127) and multibeam bathymetry data (Magofond 2 cruise), complemented by regional geophysical and geochemical datasets, provide an important opportunity to examine the processes controlling morphological and volcano-tectonic variations along the CIR. The CIR is situated on an elevated plateau formed from a temporally persistent and robust melt supply to the ridge axis. Analysis of the data shows that the fracture zones have a significant structural control on along-axis morphology and melt supply, partitioning the ridge into three morphologically defined regions. The central region (Region B) bounded by two of the fracture zones, contains segments which show rifted axial morphologies characteristic of slow-spreading ridges. Regions A and C show patterns of variable volcanic robustness along-axis associated with the supply and availability of melt to the ridge. Tectonic analysis correlates with inter- and intra-segment trends in morphology and volcanic structure, further highlighting regions of robust or deficient melt supply. Strong relationships are also revealed between the tectonic parameters of fault length, spacing and density along-axis. Finite difference analysis is used to model the Non-Transform Discontinuities along the CIR and Mid-Atlantic Ridge to understand patterns of strain within their interiors. The results indicate the presence of a damage zone ahead of a propagating segment tip, providing increased crustal permeability and a greater potential for hosting hydrothermal circulation. Analysis of geochemical data along the CIR identifies five hydrothermal plume signatures, three of which are coincident with the locations of NTDs in the study area, correlating with the findings of the numerical analysis. A detailed model of the CIR demonstrates that thermal variation influenced by ridge
structure can produce significant variations in morphology and volcano-tectonic distribution at a constant spreading rate.

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