Insights on the role of thermal stresses during the evolution of magmatic-hydrothermal systems around upper crustal intrusions, based on 2D thermo-mechanical-chemical coupled numerical models

Studies of host rock deformation near magmatic intrusions traditionally focus on stresses directly related to the intrusion process, either by directly considering inflating volumes or by considering two-phase deformation related to magma transfer. Thermal processes, especially volume changes due to thermal expansion or volume changes during partial melting/solidification are typically ignored in these studies. Here we show that thermal stresses around a rapidly emplaced upper crustal intrusion are significant and likely sufficient to create an extensive fracture network around the intrusion by brittle yielding. At the same time due to its cooling, the intrusion suffers significant decompression, resulting in low P – high T conditions, which could promote the appearance of a volatile phase. The appearance of a volatile phase and the development of a fracture network around the inclusion might be the processes that control magmatic-hydrothermal alteration around intrusions, and hence thermal stresses likely play an important role in the development of magmatic systems.

We present 2D numerical simulations of an upper crustal magma (or mush) body in a visco-elasto-plastic host rock, with coupled thermal, mechanical and chemical processes, accounting for thermodynamically consistent material parameters. The magma body is isolated from deeper sources of magma hence it is cooling, and thus shrinking. We quantify the pressure changes and stresses induced by such volume changes, and resolve fracture networks potentially developing as a result. We are considering more idealized/simplistic and more realistic geomteries and rheological, thermodynamic models alike.

We present solutions based on a self-consistent system of conservation equations for coupled thermo-mechanical-chemical processes, under the assumptions of slow (negligible inertial forces), visco-elasto-plastic deformation and constant chemical bulk composition. The thermodynamic melting/crystallization model is based on a granitic composition. We will briefly discuss the numerical implementation of thermodynamic data and volumetric plasticity (including tensile and dilational shear plasticity) in a self-consistent manner and illustrate the effect of volume changes due to temperature changes (including the possibility of melting and crystallization) on stress and pressure evolution in magmatic systems.