We are pleased to announce Alexandra Morand will be speaking at our next HotStuff seminar on the topic of: Fracturing and surface deformation in a non-elastic host rock during inflation of magmatic intrusions - Insights from Discrete Element Method modelling.

Abstract: 

Inflation of viscous magma intrusions at shallow depths in the crust of rocky planetary bodies, including Earth, often induces dome-shaped ground deformation. It also produces fracturing and compaction within the host rocks that further weaken the strength of that crust. Most models that simulate magma-induced deformation assume a homogeneous, isotropic, and linear-elastic medium wherein stress patterns indicate the potential for failure, but without simulating actual fracturing. This talk will  present a two-dimensional Discrete Element Method (DEM) model that simulates magma recharge in a pre-existing laccolith intrusion, and the induced deformation, including fracturing. In the DEM, the medium is discretised by circular rigid particles bonded together by force contact laws. Particle bonds can break at any numerical timestep and thus fractures can propagate during magma intrusion in our model. We numerically investigate the effect of the host rock toughness (resistance to fracturing) and stiffness (resistance to deformation) and of the intrusion depth, on stress, strain, spatial fracture distribution, and surface displacements. Our results show that the spatial fracture distribution varies between two end-members: (1) for low stiffness or high toughness host rock or shallow intrusion: limited cracking, one central vertical fracture initiated at the surface, and two inward-dipping fractures at the intrusion edges; and (2) for high stiffness or low toughness host rock or deep intrusion: extensive cracking, multiple vertical surface fractures propagating downward and two inward-dipping highly cracked shear zones that connect the intrusion tip with the surface. Abrupt increases in surface displacement magnitude occur in response to fracturing, even at constant magma injection rates. Our model provides a novel approach to consider host rock mechanical strength and fracturing during viscous silicic magma intrusion and associated dome-shaped ground deformation. We can expect this new model’s findings to help understand fracture distribution patterns in magmatic hydrothermal systems on Earth, but also magma emplacement mechanisms on other rocky planetary bodies.