THERMAL-DIFFUSIVITY OF THE LITHOSPHERE DERIVED FROM ALTIMETRY AND BATHYMETRY PROFILES ACROSS THE SOUTHWEST INDIAN RIDGE

In standard models for computing oceanic lithosphere thickness, the lithosphere's thermal diffusivity is one of the basic parameters required and present estimates have a substantial uncertainty. Extending the work of Crough [1979], Lister [1982] and Gibert and Courtillot [1990], we propose a new method for the determination of thermal diffusivity of oceanic lithosphere in the near-ridge crest domain. The method requires geoid height and depth data, both of which reflect wavelengths associated with the lithospheric cooling process and expressed as a function of seafloor age. Over the Southwest Indian Ridge, the thermal diffusivity so found [(0.55+/-0.17)x10(-2)cm2s-1] is consistent with data from the South Atlantic. Differences in diffusivity calculated on either side of the ridge and caused by asymmetrical subsidence are possibly linked to a differential thermal regime beneath the ridge and/or to the general motion of the ridge. Our findings are interpreted in terms of a lithospheric boundary layer less than 14age1/2 kmMyr-1/2 thick and initial temperature between 1050 and 1390-degrees-C.