Revised Oceanic Plate Cooling Models

Abstract

Global age-depth and heat flow observations provide constraints for cooling and subsidence of oceanic plates. Numerous studies have addressed this problem, which has a bearing upon the calibration of shear-wave tomographic models and upon lithospheric rheology. The robustness of these results depends upon the quality and spatial distribution of both age-depth and heat flow measurements. Here, we revisit the plate cooling model for two reasons. First, a database of 10,863 age-depth measurements that are distributed throughout the oceanic realm has been constructed. This database is combined with 3,573 heat flow measurements. Second, we wish to explore a range of analytical and numerical plate models that incorporate the temperature- and pressure-dependence of conductivity, of expansivity, and of specific heat capacity. Our goal is to identify plate models that jointly fit observational constraints, whilst honoring laboratory-based estimates of key thermal parameters. Both simple analytical and comprehensive numerical parameterizations recover an equilibrium plate thickness of $105\pm 10$ or $96\pm 10$ km with a temperature of $1,326\pm 50°$C. This recovered temperature is consistent with independent petrologic constraints. Spatial analysis of age-depth measurements demonstrates that previously invoked transient plate shallowing is not globally observed. This observation implies that the possible onset of a convective instability, which has been proposed as a mechanism to stabilize equilibrium plate thickness, might act on shorter length scales than that implied by previously reported transient shallowing. Finally, our revised plate model is used to track lithospheric thermal structure as a function of time and to calculate residual depth anomalies.