Application of Seasat Altimetry to Tectonic Studies of Fracture Zones in the Southern Oceans.

摘要

Gravity derived from Seasat altimetry provides a means of estimating seafloor topography and its compensation, which in turn can be used to understand the evolution of oceanic lithosphere. First, the correlation between the geoid, deflection of the vertical, and seafloor topography is investigated along a section of the Southwest Indian Ridge. Geoid anomalies computed from a simple thermal model fairly accurately predict the intermediate-wavelength anomalies across the fracture zones. Next, fracture zones along the Southwest Indian Ridge are identified using altimeter profiles and bathymetry. Finite poles of rotation are determined from the fracture zone locations and magnetic anomaly lineations for anomalies 6 (20 Ma), 13 (37 Ma), and 20 (45 Ma). The new poles are in general agreement with previously published poles and describe a fairly consistent direction of relative motion between Africa and Antarctica for the past 45 Myr. In the 3rd study, rate of change of the geoid with age was estimated as a function of age from geoid offsets across the Eltanin and Udintsev fracture zones and used to constrain thermal models of lithosphere cooling. Observed trends in the geoid slope vs age plots are similar on both branches of the Eltanin and the east limb of the Udintsev fracture zone. The similarity in trends argues against the effects of isolated thermal or bathymetric anomalies and appears instead to reflect a general feature of the geoid-slope versus average age relationship across fracture zones.