Investigating feedbacks between magmatic emplacement, relief development, and surface processes at continental rifts

Abstract:

Magmatic accommodation of strain during continental rifting is challenging to simulate in numerical models. Individual diking events typically occur over hours to weeks, a timescale that is not well captured in numerical tectonic simulations with timesteps on the order of thousands of years or more. The locus and magnitude of magmatic emplacement is also expected to evolve in response to the ambient stress. To meet these challenges, we present a new method for simulating magmatic injection in 2-D numerical models of continental rifting environments that treats magmatically-robust regions as zones of distributed "plastic-like" yielding, which expand when a tensile stress threshold is met, thereby accommodating extensional strain via material injection. The modeled region of magmatic extension responds to the evolving lithospheric stress field due to faulting and topographic growth, as well as topographic redistribution by erosion and sedimentation.

Using the magmatic distributed yielding model, we demonstrate feedbacks between magmatic intrusions, tectonic movements, and surface processes. Within these feedbacks, magmatic overpressure and the efficiency of surface processes are key controls affecting rift evolution. Model results indicate that the distribution of magmatism along a rift is sensitive to fault-derived topographic growth. Specifically, dike intrusion becomes less favorable at depth and shallows as rift topography grows. In turn, magmatic focusing reduces the proportion of strain accommodated at shallow depths along faults. By leveling relief, efficient surface processes thus have the potential to alleviate this feedback and allow deeper intrusions over a longer time span.