A magma accretion model of oceanic lithosphere is proposed and its implications for understanding its thermal field examined. The new model (designated Variable Basal Accretion—VBA) assumes existence of lateral variations in magma accretion rates and temperatures at the boundary zone between the lithosphere and the asthenosphere. However, unlike the previous thermal models of the lithosphere, the ratio of advection to conduction heat transfer is considered a space dependent variable. The results of VBA model simulations reveal that the thickness of the young lithosphere increases with distance from the ridge axis, at rates faster than those predicted by Half-Space Cooling models. Another noteworthy feature of the new model is its ability to account for the main features in the thermal behavior of oceanic lithosphere. The improved fits to bathymetry have been achieved for the entire age range and without the need to invoke the ad-hoc hypothesis of large-scale hydrothermal circulation. Also, use of VBA model does not lead to artificial discontinuities in the temperature field of the lithosphere, as is the case with GDH (Global Depth Heat Flow) reference models. The results suggest that estimates of global heat loss need to be downsized by at least 25%. 1. Introduction Detailed understanding of large-scale variations in the thermal field of the oceanic lithosphere provides important constraints on deep tectonic processes. Nevertheless, thermal models of the lithosphere proposed to date have failed to provide a satisfactory account of some of the important features of large-scale variations in oceanic heat flow. For example, both the Half-Space Cooling [1] and Plate [2] models predict heat flow much higher than the observed values, for young (ages less than 55？Ma) ocean crust. Also, the magnitudes of heat flow anomalies associated with the mid-ocean ridge systems are systematically lower by a factor of 6 at younger ages than those predicted by thermal models proposed in the current literature [3]. In addition, the widths of thermally anomalous zones associated with the spreading centers are narrower (less than 23？Ma) than those calculated (~66？Ma) for a wide range of plausible model parameters. Such discrepancies between model predictions and observational data have given rise to the so-called “oceanic heat flow paradox”, for which no satisfactory solution has been found for over the last forty years. The common practice in the current literature is to consider the paradox as originating from eventual perturbing effects of possible regional scale
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