The relationship between depth, age and gravity in the oceans

Abstract

S U M M A R YWe reassess the applicability of the thermal plate cooling model to the subsidence of the North Pacific, Atlantic and North Indian Ocean Basins. We use a new numerical plate model in which the thermophysical parameters of the lithosphere vary with temperature according to the results of laboratory experiments, and the ridge temperature structure is consistent with the thickness of the oceanic crust. We first attempt to exclude thickened crust from our data set, and then to exclude swells and downwellings by masking regions of the data that remains that have significant gravity anomalies when there exists a clear regional correlation between intermediate-wavelength gravity and topography. We find that the average variation of depth with age is consistent with conventional half-space models until about 90 Myr. Thereafter, the departure from the half-space cooling curve is more rapid than predicted using simple conductive plate cooling models. The depth-age curves in the Pacific and Atlantic show ∼250 m of temporary shallowing between the ages of 90-130 Myr, a result consistent with the outcome of experiments on the initiation of small-scale boundary layer convection. The results do not change significantly if the estimated component of the gravity arising from plate cooling is subtracted prior to calculation of the correlation between gravity and topography. A 90-km-thick conductive plate is nevertheless a reasonable model for the average temperature structure of the oldest part of the Pacific ocean lithosphere. In the Pacific, the broad topographic undulations associated with the Line Island Swell, the Hawaiian Swell and surrounding basins have correlated gravity anomalies and an admittance of approximately 30 mGal km −1 and are likely to result from convective circulation in the upper mantle. In the Northeast Atlantic, the intermediate-wavelength admittance over the Cape Verde swell is similar; in the Northwest Atlantic over the Bermuda Swell it is slightly larger but not as well constrained.

Submarine Geomorphology

“…Consequently, the number and dimensions of the volcanoes themselves are better estimated. Techniques such as identifying the deepest of multiple modes [Crosby et al, 2006], or using directional medians on gridded data [Kim & Wessel, 2008], have improved results further. Problems, however, remain; mainly i) 'spectral overlap' or the sharing of width-scales with other seafloor features [Wessel, 1998], which prevents simple approaches that can succeed in isolating some superimposed landforms [Hillier & Smith, 2008] ii) width-scale selection, which has not been automated as would be necessary for optimally separating each individual edifice in a large population.…”

Geophysical and petrological constraints on ocean plate dynamics

“…Depth-age relationships of oceanic plates are useful in determining asymptotic plate thicknesses [Parsons and Sclater, 1977;Stein and Stein, 1992;Crosby et al, 2006], and with a carefully chosen dataset, can help verify our calculated mantle plate thickness and basal temperature.…”

3.11 Geovisualization

“…However if normal elevations are rare, perhaps where there are many volcanoes and little remaining original seafloor, bias can occur underestimating heights and volumes in the residual (Smith, 1990). 'Robust' statistics such as the median and mode can mitigate this substantially (Smith, 1990, Crosby, 2006Kim & Wessel, 2008), as can iterative statistical approaches (Marty & Cazenave, 1989;Wang et al, 2001). …”