A MATLAB-derived software (geothermMOD1.2) for one-dimensional thermal modeling, and its application to the Corsica-Sardinia batholith

Abstract: Determination of the thermal state of the crust is of fundamental importance to understand the feedbacks between tectonics, rheology and metamorphism. The most important parameters controlling the variation of temperature with depth in the crust are the heat flow across the Moho, the thermal conductivity and the vertical distribution of heat-producing elements 238,235U, 232Th and 40K. The Corsica-Sardinia batholith formed during a regional high-temperature metamorphic event by extensive partial melting of the Variscan crust. Petrologic observations indicate that most granites and migmatites formed between 0.6–0.2GPa, requiring the geotherms to flatten substantially relative to the stage of crustal thickening. The adjustment of geotherms may be interpreted in terms of enrichment in heat-producing elements or, alternatively, in terms of increased mantle contribution. The validity of these two end-member hypothesis has been tested by performing numerical experiments with a software package appositely developed in Matlab. The software allows to set up crustal model composed of up to five different layers, and to plot the calculated geotherm along with the stability field of the haplogranite system and other thermo-barometric constraints. The steady-state thermal structure of the Sardinian Variscan crust has been computed at four different time steps (320, 310, 300, and 280Ma), which cover the batholith evolution. The geometry and composition of each of these crustal models has been constrained based on geophysical observations, geochronology and petrology. In a first experiment, the heat conduction equation has been solved for all of the four time-steps, assuming constant (15mW/m2) heat flow across the Moho in order to simulate a ‘fully crustal’ evolution of the thermal structure. The alternative has been simulated in a second experiment, by rising the basal heat flow up to 40mW/m2 during the last two time steps. [Copyright &y& Elsevier]