On heat flow singularities over mid-ocean ridges

Abstract

Current interpretations of heat flow values within the framework of plate tectonics concepts fail to reproduce the available observations for the oceanic ridge crests and give heat flow singularities. A new mathematically tractable theory of vertical intrusion (using a non-uniform temperature distribution at the ridge crest) has been constructed that shows a reasonable fit between predicted and observed heat flows. In this theory the derived heat flow is finite everywhere. It should serve as a useful starting point in the inverse problem of deriving the temperature distribution with depth on the basis of surface evidence. The plate model currently used assumes vertical intrusion at a uniform temperature to create crust at the oceanic ridges. This simple model does predict such features as the topography and the high heat flow in the ridge crest areas, but it has some deficiencies, including a discrepancy between observed and theoretical heat flow profiles; in particular, the model predicts infinite heat flow in the narrow zone where new lithosphere originates, so that the predicted relationship between the lithospheric thickness and the heat flow half width is valid only far away from the ridge axis. Previous models give rise to infinite heat losses, and the lithospheric thickness is a free parameter not determined by the physics of the problem. In this paper we introduce a new model that overcomes the difficulties involved in previous models. A new parameter is involved, which we interpret physically as the level of hot solid material above the melt column going from the bottom of the lithosphere. Observed data on maximum heat flow values at the ridge crest are used to determine this parameter. The lithospheric thickness in a given region can be determined by the way in which the heat flow decreases along the ridge flanks. Heat losses for the oceanic ridges are calculated in our nonsingular model by separating out the anomalous two-dimensional part of the temperature and heat flow field. Thus a heat loss for ocean ridges amounting to 0.2–0.3 of the global heat loss is given.