The controls on the thermal evolution of continental mountain ranges

This contribution will describe a new suite of models that we have produced in order to investigate the controls on the thermal evolution of continental mountain ranges. In particular, we have examined which parameters (e.g. relating to the rate and geometry of mountain building and erosion, and the distribution of radiogenic heating) control which aspects of the thermal evolution. By making use of modern computing power, we have produced many models of all combinations of input parameters, in order to produce a wide range of model pressure-temperature-time paths (for tens of thousands of parameter combinations). By examining which selection of these model results are consistent with the pressure and temperature conditions experienced by rocks exhumed from the depths of mountain ranges, we are able to estimate the range of parameters that are consistent with the observed metamorphic assemblages, and deduce how to extract the maximum possible amount of information about the evolution of a mountain range from estimated pressure-temperature-time paths. We find that the majority of Phanerozoic mountain-building is likely to have been accomplished by thickening above rigid underthrusting foreland lithosphere, rather than by homogenous thickening of the entire crust. The curvature of pressure-temperature loops allows us to estimate the rates of crustal thickening and erosion, and the average rate of radiogenic heating. We illustrate these concepts using observations from a variety of modern and ancient mountain ranges (e.g. the Scottish Caledonides, the Alps, and the Canadian Cordillera). Our results have implications for understanding the rates of evolution of mountain ranges, their rheology (both in terms of the evolution of rheology in the deforming mountain range, and also the presence or absence of rigid underthrusting foreland lithosphere), and for using the geological record to establish how far back in time mountain building has resembled that at the present day.