INFLUENCE OF PULSED MAGMATIC ACTIVITY, LATENT HEAT, AND PARTIAL MELTING ON THE STRENGTH OF THE CONTINENTAL CRUST

Arc magmatism can influence the rheological properties of the crust by decreasing its strength. The intruding magma heats and melts the surrounding country rock, which decreases the effective viscosity of the material both in the solid and partially molten state. This reduced strength has the potential to affect subsequent deformation, which in turn can further work as a feedback mechanism that influences magmatic activity.

Here we quantify the effects of magmatism on crustal strength using a finite difference solution to the 2D heat conduction equation coupled to a series of 1D crustal (visco-plastic) strength envelope models, and including pulses of magmatic activity, latent heat, and the influence of melt fraction on the rock effective viscosity. We assess the importance of different model parameters on the crustal strength by varying factors including the active time of the intruding magma reservoirs, their temperatures, compositions, melt fractions, and the distances between different magmatic systems. Each rock composition has different material properties, such as their density, heat capacity, latent heat, and mechanical properties. Melt fractions for different temperatures and pressures have been acquired using the rhyolite-MELTS software (Gualda et al., 2012) for felsic, intermediate, and mafic compositions. The decrease in viscosity from partial melting of the rock is calculated using a viscosity model for a solid with fluid-filled pores (Schmeling et al., 2012).

Using cooler felsic intrusions in the model, and not including the latent heat of crystallization or melting of the rock, magmatism can reduce the integrated crustal strength by roughly 30%. For hotter basaltic and intermediary compositions, the crustal strength can decrease as much as 45%. By including the effects of latent heat and reduced viscosity for various melt fractions, it is expected that the crustal strength would be reduced even further. Including the latent heat will cause the intrusions to remain hot for longer. The production of melt results in a substantial drop in the rock viscosity, and more than 10% of melt can decrease the crustal strength by 50% in some cases. Quantifying the effects of the melt fraction data and the latent heat are the focus of on-going work.