Carlsberg Ridge, northern Indian Ocean: gravity and isostasy

Abstract

SUMMARY Gravity and bathymetry profiles across the Carlsberg Ridge in the Indian Ocean are analysed to investigate the isostatic compensation of this part of the Indian Ocean spreading ridge system. The ridge has a rough flanking topography and a median valley, which are the characteristics of slow-spreading ridges. We use the crossspectral technique to obtain an admittance function for isostatic studies. Admittance estimates in the long-wavelength region (125-500 km) indicate that the elastic plate thickness supporting the long-wavelength topography is in the range 5-10 km. We have also examined the isostasy of the axial region. Synthetic topography and gravity profiles computed for a cooling plate model are subtracted from the observed, to estimate the median valley signatures. The residual gravity anomaly over the ridge axis is mostly explained by the median valkey topography with a uniform crustal thickness of 6 km, indicating that the median valley is not in isostatic equilibrium.