Effects of an extensional tectonic stress on magmatic reservoir failure and magma propagation within the Venusian lithosphere

Abstract:

Failure of magmatic reservoirs and propagation of magmas is controlled in part by the state of stress within the lithosphere. Such stresses are induced by a range of loadings (e.g., gravitational and magmatic). Additional stresses can be introduced by flexural deformation of the lithosphere due to a large volcanic edifice or mantle plume loading, or as a consequence of the regional tectonic environment. Rifting environments, for instance are the results of extensional stresses at the surface of planets (e.g., Devana Chasma on Venus). The resulting stress field may influence the failure of a magmatic reservoir and the propagation of magmas.

To explore this scenario, we created 3D elastic models of the Venusian lithosphere using COMSOL Multiphysics, in which an extensional stress was applied. The stress state was implemented through horizontal deformation created by orthogonal contraction and extension on the outer boundaries of the quarter symmetry model. A spherical reservoir is embedded within the lithosphere to represent a magma chamber. In these models, we analyzed magma reservoir stability at different depths, the amount of overpressure needed to reach failure, and the type of resulting intrusions within the 3D model for three distinct environments: 1- lithostatic; 2- upward flexure due to a rising mantle plume; and 3- downward flexure due to a basaltic shield volcano.

Preliminary results show that as the extensional stress increases: magmatic reservoirs become unstable at shallow depth and the amount of overpressure needed to reach failure decreases. In addition, the failure location along the reservoir flank rotates to parallel the horizontal contraction, which favors the formation of lateral dikes along the magma reservoir flanks over vertical dikes at the summit.