The Influence of Variable Host Rock Cohesion and Magma Viscosity on Intrusion-Fault Interaction: Insights From Laboratory Models

Abstract

Magma transport through the Earth's shallow crust can be affected by pre-existing weaknesses like faults. Consequently, fault-channeled magma may reach the surface in unexpected locations. Hence, better understanding of magma-fault interaction is needed to improve hazard assesment. We investigate the effect of host rock cohesion and magma viscosity on intrusion-fault interaction using laboratory experiments. Vegetable oil and glucose syrup, serving as low- and high-viscosity analogue magmas, were injected into intact and faulted granular materials with variable cohesion (mixtures of silica flour and micro-glass beads), serving as a brittle plastic model crust. High-cohesion models produced sheet intrusions, that propagated along fault segments upon intersection. Low-cohesion models produced low-aspect ratio intrusions low width/thickness ratio. Without tectonic stresses, the cohesion strongly controls intrusion-fault interaction, while tested model magma viscosities exerted a weaker control. Our findings show that intrusion-fault interaction is a highly complex process and important to consider at active volcanoes.