POSTINTRUSIVE THERMAL EVOLUTION OF CONTINENTAL-CRUST - A MOVING BOUNDARY APPROACH

Intrusion of magmatic bodies into continental crust has been extensive ly used to explain high heat flow, anomalous seismic velocity structur e, and gravity anomalies. These intrusions significantly control the c rustal deformation by modifying the heat and mass budget of the crust. However, thermal modeling results based on simple cooling of intrusiv es ignore the effect of moying boundaries during magma solidification. In the present work we discuss a mathematical formulation of the ther mal evolution of continental crust in presence of such magma solidific ation process. The solution is obtained by using the Fourier spectral approach in the space domain and a modified finite difference scheme I n time domain. This solution provides the cooling history and thermal evolution within an intrusion unlike the solutions proposed earlier to adjust the effect of latent heat of intrusion in the form of apparent specific heat or apparent temperature of intrusion and is a general o ne in the sense that this includes the radiogenic heat sources distrib ution and an initial depth dependent temperature distribution in litho sphere. We apply this solution to study the thermo-theological evoluti on of continental lithosphere after magmatic underplating. We conclude that this effect keeps the intrusive body and the surrounding rocks a t a higher temperature for a longer duration than when the effect is i gnored or is adjusted in the form of increased specific heat. For an i nitially ductile lower crust and brittle upper mantle, magmatic underp lating causes a change in the mode of deformation from brittle to duct ile in the mantle layer and the latent heat effect included in the for m of moving boundaries prolongs the duration of ductile deformation in this layer in comparison to the latent heat effect adjusted by increa sing the specific heat of intrusion. The prolonged duration of ductili ty in lower crust/upper mantle due to the slow cooling of intrusion re sults in a weak lithosphere and is important in addressing the issues concerning crustal dynamics.