A new model of deformation and dynamic fracturing above laccolith intrusions

High-viscosity magma can form laccolith intrusions that deform and fracture the overburden, causing surface uplift and ground fracturing. Laccolith-induced deformation features have been described at well-exposed outcrops of long-solidified intrusions. The lack of recent geophysical data on rare laccolith emplacement events and the use of linearly elastic continuum-based numerical models precludes a clear understanding of the dynamic fracturing mechanisms. We present a new two-dimensional (2D) Discrete Element Method (DEM) approach to dynamic magma intrusion in a particle-based host medium. The model indicates highly discontinuous deformation and dynamic fracturing and visualizes the localization of subsurface strain. We calibrate the numerical rock strength parameters by performing numerical laboratory experiments to natural rock strength values. We systematically explored the effect of numerical parameters that govern host rock strength (bond cohesion, bond tensile strength, bond elastic modulus), and intrusion depth, on the spatial distribution of strain, stress, and fracturing. We find that high host rock stiffness results in widely distributed and dense fracturing associated with symmetrical dome-shaped surface uplift. Low host rock stiffness results in the concentration of central fracturing and narrow lateral shear bands and asymmetric evolution of the laccolith geometry and the surface deformation pattern. These patterns are affected by the intrusion depth. Our models help understand fracture distribution patterns above laccolith intrusions and open unprecedented opportunities for dynamically modelling intrusion-induced deformation in the upper few kilometers of the Earth’s crust.