Crustal Magma Reorientation

While the geodynamic environment of magma reservoir highly influence the stability of magma reservoir and the propagation of magmas within the lithosphere, volcanic eruptions themselves can transform the local environment leading to changes in the state of stress within the crust (e.g., caldera formation [Corbi et al., 2016]). These changes in the state of stress can promote the reorientation and the diversion of magmas allowing potential eruptions away from the original volcanic center [Lefebvre et al., 2012; Maccaferri et al., 2014; Maccaferri et al., 2017]. Observations at eroded monogenetic volcanic fields can provide tremendous information on the magmatic plumbing systems underlying these systems, specifically diversion of magmas from vertical to lateral propagation have been observed at the base of eroded diatreme structures [Muirhead et al., 2016]. These information can be used to decipher the eruptive mechanisms influencing magma propagation and magma diversion within the crust [Le Corvec et al., 2018; Zorn et al., 2019].

Using the stress transfer methodology in COMSOL Multiphysics® that allows the transfer of the stress tensor and the deformed geometry from one model to another, I modeled two successive steps modeling the excavation of a diatreme (Fig. 1.1) and its subsequent filling (Fig 1.2).

Figure 1: Two step finite element model: Step 1. The proto-diatreme (aka excavation stage) and Step 2. developing diatreme (aka infilling stage). a. Finite element model configuration. b. State of stress within the diatreme’s infill and the surrounding crust. Blue and red shadings represent extensional and compressional Δσ_tect, respectively. Based on Melosh and Williams [1989] and McGovern and Solomon [1993], the hourglass shapes are oriented along the direction of greatest compressive stress (σ₁); the red bars along the direction of least compressive stress (σ₃). Circles represent out-of-the plane hourglass shapes (σ₁ perpendicular to the r–z plane). c. Sketch of a maar-diatreme eruption and formation of the magmatic plumbing system. The colored arrows represent the orientation of the minimum compressional stress (σ₃), the blue and red colors represent the differential tectonic stress, extensional and compressional, respectively. Reworked from Le Corvec et al. [2018].