Models of buoyancy-driven dykes using continuum plasticity or fracture mechanics: a comparison

Abstract

Magmatic dykes play an important role in the thermomechanics of tectonic rifting of the lithosphere. Our understanding of this role is limited by the lack of models that consistently capture the interaction between magmatism, including dyking, and tectonic deformation. While linear elastic fracture mechanics (LEFM) has provided a basis for understanding the mechanics of dykes, it is difficult to consistently incorporate LEFM into geodynamic models. Here we further develop a continuum theory that represents dykes as plastic tensile failure in a two-phase Stokes–Darcy model with a poro-viscoelastic–viscoplastic (poro-VEVP) rheological law (Li et al., 2023). We validate this approach by making quantitative comparison with LEFM, enabled by a novel formulation for buoyancy-driven porous dykes (poro-LEFM). The comparison shows that dykes in our continuum theory propagate slowly – a consequence of Darcian drag on the magma. Moreover, dissipation of mechanical energy in the poro-VEVP model implies a high critical stress intensity in LEFM. We improve the poro-VEVP model by reformulating the compaction stress and incorporating anisotropic permeability in regions of plastic failure.