EFFECTS OF TEMPERATURE-DEPENDENT MATERIAL PROPERTIES AND RADIOACTIVE HEAT-PRODUCTION ON SIMPLE BASIN SUBSIDENCE MODELS

The effects of applying laboratory-derived material parameters to simp le thermal basin subsidence models are examined. The temperature-depen dent properties of thermal conductivity, specific heat and the coeffic ient of thermal expansion are considered, as well as conductivity cont rasts between the crust and mantle and lithosphere-scale radiogenic he at production. The effects of conductivity and radioactivity are compl ementary, and can be predicted from the way in which they influence th e initial and final steady-state geothermal gradient. A convex-up init ial gradient, such as is generated by the conductivity and radioactivi ty functions and is also assumed to be the case based on independent e vidence, will lead to more initial subsidence than in a simple constan t-parameter model. The final subsidence will also be greater in the mo dified model, due to the fact that the stretching event will result in a lithospheric column which is intrinsically cooler than in the pre-d eformation case. Because the coefficient of thermal expansion rises wi th increasing temperature, including its temperature dependence will r esult in a model with substantially less initial subsidence than one w ith a constant value. When these parameters are combined into a single model, the initial subsidence is approximately 15-20% less than in th e constant-parameter model if radioactivity is not included, and 10% l ess if it is, while the final subsidence is about 5% greater without r adioactivity and 7-9% greater with radioactivity included. Depending o n the magnitude of extension, these effects can translate into differe nces of tens to hundreds of meters when compared to the constant-param eter model.