Straight from the Source: Towards Simulation of Dike Injection Governed by Melt Supply in Long-Term Tectonic Models

Magmatic diking profoundly alters the evolution of lithospheric structure and tectonic processes. Yet, simulating diking in long-term tectonic models presents numerical and theoretical difficulties due to the large spatiotemporal differences between a dike event and plate-boundary scale processes. Parameterizations, such as the ratio of magmatic to tectonic accretion often used in mid-ocean ridge simulations have yielded key results, but do not yet connect dike injection to the available magma supply. In this work, we seek to do so using a dike injection rate modulated by material compressibility and triggered by accumulation of sub-crustal melt pressure.

We use the finite element code ASPECT to simulate dike injection within an incompressible material analogous to the oceanic lithosphere and subject to a visco-plastic rheology. Initial diking tests are performed in an isothermal, cross-sectional domain measuring 1.1 km by 1 km box with free slip horizontal and open vertical boundaries. Within our model, dike injection is triggered when the pressure within a simple box-model magma chamber exceeds a critical value. Once triggered, diking occurs within a vertical line of elements located at the center of the horizontal axis. Within these elements we impose a pressure rate of diking calculated by multiplying an a-priori pressure per dike by the discrete number of diking of events required to reduce the magma chamber pressure below the critical threshold. The resulting pressure rate multiplied by the material compressibility yields a dilation rate implemented as a source term in the conservation of mass equation. Additionally, a compressibility term is added to the conservation of momentum equation to ensure mass is conserved appropriately. Initial tests with constant timestep size, melt accumulation rate, and pressure per diking event yield predicted constant horizontal extension rates. We present these test results as well as additional runs of varying, time-dependent melt accumulation and per dike pressures. Furthermore, we explore the physics connecting dike pressure and melt accumulation and invite discussion on applications of this method to specific geologic settings including, but not limited to, the role magmatism plays in faulting modes at mid-ocean ridges.