Intermediate-complexity modeling of magma–tectonic interaction in continental rifts

Continental rifting often induces decompression melting and the ascent of magma that intrudes into the brittle crust in the form of dikes and sills and that extrudes along volcanic fields. At the same time, continental rifts experience stress from topographic loading due to rift flank uplift. It is clear that these two processes interact in magmatic rifts such as the Kenya Rift, the Main Ethiopian Rift, the Afar triple junction, and at the Icelandic plate boundary. However, separating the interplay between tectonic and magmatic processes, the evolving topography and the rift-related stress field, as well as the impact of these processes on dike-fault interactions from field observations alone remains difficult.

Previous modeling studies of time-dependent magma-tectonic interactions in extensional tectonic settings generally fall into two categories: (1) Simple models (e.g. Buck et al., 2005) represent diking by a prescribed fixed rectangular zone of horizontal divergence. While this approach can be applied to model tens of millions of years of dike injection along spreading ridges, its simplicity prevents applications to continental rifts where magmatism manifests over broad areas. (2) More complex setups simulating magma ascent via porous flow and fluid-driven fracture (e.g., Li et al. 2023). This approach allows to study the evolution of individual dikes, but its computational costs prevent application to lithosphere-scale rifts over geological time scales. 

Here, we present a numerical workflow that can be categorized as a model of intermediate complexity. The dikes are nucleated at the brittle-ductile transition above zones of partial melt. They are then propagated perpendicular to the minimum compressive stress, similar to the approach of Maccaferri et al. (2014), until they reach their freezing depth or the surface. In this presentation, we show how we  approach this problem and how we implement it in the open-source community geodynamics model ASPECT. We demonstrate that the generated dikes are being focused in specific regions, and how the directional dilation and heat injection during magma intrusion through dikes influence the long-term rifting evolution. 

References:

Buck, W. Roger, Luc L. Lavier, and Alexei N. B. Poliakov. “Modes of Faulting at Mid-Ocean Ridges.” Nature 434, no. 7034 (April 2005): 719–23. https://doi.org/10.1038/nature03358.

Li, Yuan, Adina E Pusok, Timothy Davis, Dave A May, and Richard F Katz. “Continuum Approximation of Dyking with a Theory for Poro-Viscoelastic–Viscoplastic Deformation.” Geophysical Journal International 234, no. 3 (September 1, 2023): 2007–31. https://doi.org/10.1093/gji/ggad173.

Maccaferri, Francesco, Eleonora Rivalta, Derek Keir, and Valerio Acocella. “Off-Rift Volcanism in Rift Zones Determined by Crustal Unloading.” Nature Geoscience 7, no. 4 (April 2014): 297–300. https://doi.org/10.1038/ngeo2110.