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Geoid and depth anomalies over ocean swells and troughs: Evidence of an increasing trend of the geoid to depth ratio with age of plate

1988; American Geophysical Union; Volume: 93; Issue: B7 Linguagem: Inglês

10.1029/jb093ib07p08064

2156-2202

Anny Cazenave, K. Dominh, M. Rabinowicz, Georges Ceuleneer,

Geomagnetism and Paleomagnetism Studies

Medium‐wavelength (1000–4000 km) geoid and depth anomalies are positively correlated over a number of oceanic features. We have computed the geoid to topography ratio (or admittance) over 28 areas covering midplate swells, deep‐sea troughs, and aseismic plateaus after correcting the data for lithospheric cooling effects and for sediment loading. The observed admittances range from ∼ 1 to ∼ 5 m km −1 depending upon the area considered. Aseismic plateaus have a low admittance, consistent with Airy compensation by crustal thicknening. Larger admittances are observed above mid‐ocean swells and ocean deeps. For these latter features a linearly increasing trend with the square root of plate age of is observed. Linear regression indicates an admittance increase of 0.53 m km −1 per (m.y.) 1/2 . Observed admittances are consistent with dynamic support by convective upwellings and downwellings, provided that a shallow, low‐viscosity layer exists beneath the lithosphere. According to recent convection modeling, the observed admittance increase with age may be understood either in terms of viscosity, increase of the low‐viscosity layer, from ∼ 10 −2 at mid‐ocean ridges to ∼ 1 in old basins (mean upper mantle viscosity taken as reference) or in terms of thickness increase of the lithosphere at the expense of a low‐viscosity layer of constant viscosity.