The heat flow—heat generation relationship: Implications for the nature of continental crust

Abstract

Abstract The apparent linear relationship between surface heat flow, Q and heat generation, A, is usually interpreted in terms of heat flow provinces i.e., terrains that have a common tectonothermal history and a uniform mantle component of heat flow. The slope, D, of the linear regression of heat flow on heat generation is an indication of the thickness of the upper heat-producing layer. For many terrains D is numerically similar to the depth of a major mid-crustal transition zone. These observations are modelled by a two-layer crust consisting of an upper layer, approximately 10–15 km thick, of variable heat generation, underlain by a layer about 20 km thick in which heat generation is lower and more uniform than that in the upper layer. The model is well able to simulate Q-A regression parameters for different sets of real data. It is also consistent with other geological and geophysical observations. The higher and more variable heat generation of the upper layer is consistent with ideas concerning removal of heat-producing elements from the lower layer during amphibolite to granulite metamorphism and their redistribution into the upper crust. Further redistribution of heat-producing elements may occur in zones of hydrothermal circulation whose depth is a function of stress, pressure and temperature, and which may migrate vertically in response to stress changes during uplift and erosion. Large-scale metamorphism to granulite facies has been postulated as one mechanism for stabilisation of continental crust in the late Archaean. It is shown, however, that redistribution of heat-producing elements in such a process would have only a small effect on crustal geotherms, so that partitioning of heat production was not a major factor in the crustal stabilisation.