Localization of geoid anomalies and the evolution of oceanic lithosphere: A case study from the Mendocino Fracture Zone

The thermal evolution of oceanic lithosphere is investigated by focusing on geoid offsets occurring across the Mendocino Fracture Zone, where plates with different ages are juxtaposed. Various processing techniques have been devoted to separate the geoid signal of the age contrast from regional and shorter wavelength components unrelated to the thermal structure of lithosphere. Nevertheless, due to processing differences, estimates of geoid offsets vary, and no agreement on the thermal evolution of oceanic lithosphere has been found so far. In this study, we propose to use a continuous wavelet analysis to accurately characterize the components of the geoid at different spatial scales and to estimate a new geoid slope-age relationship from localized signals. We also apply the same wavelet transform on a set of synthetic geoid calculated with different assumptions on plate cooling. The comparison of the observed geoid offsets with those predicted from cooling models indicates that our approach can successfully remove unwanted regional contributions and isolate the geoid signature due to lithospheric cooling. Our results suggest that, contrary to previous studies, geoid slopes measured at the Mendocino Fracture Zone are compatible with both the half-space cooling model and the plate model.