Effects of crustal-scale mechanical layering on magma chamber failure and magma propagation within the Venusian lithosphere

Abstract

Understanding the connection between shallow subsurface magmatism and related surface expressions provides first-order insight into the volcanic and tectonic processes that shape a planet's evolution. When assessing the role of flexure, previous investigations assumed homogeneous host rock, but planetary lithospheres typically include crust and mantle material, and the mechanical response of a layered lithosphere subjected to flexure may influence both shallow magma reservoir failure and intrusion propagation. To assess the formation of giant radial dike systems, such as those observed on Venus, we create axisymmetric elastic finite element models of a spherical reservoir centered at the contact between stiff, dense mantle overlain by softer, lighter crust. We analyze magma chamber stability, overpressure at rupture, and resulting intrusion types for three distinct environments: lithostatic, upward flexure, and downward flexure. In the lithostatic case, reservoir failure at the crust-mantle contact favors lateral sill injection. In the flexure cases, we observe that failure location depends upon the crust/lithosphere thickness ratio and, at times, will favor radial dike intrusion. Specifically, upward flexure can promote the formation of giant radiating dike swarms, a scenario consistent with a plume-derived origin. Our results present a mechanical explanation for giant radial dike swarm formation, showing that both the stability of magma chambers on Venus and the type of intrusions that form are influenced by lithospheric layering. Furthermore, where dike swarms occur, our approach provides a powerful new way to constrain local crust/mantle layering characteristics within the lithosphere at the time the swarm was forming.

Varying styles of magmatic strain accommodation across the East African Rift

“…This plays a particularly important role when preexisting fracture planes are normal to the least compressive stress (σ 3 ) [ Delaney et al ., ; Jolly and Sanderson , ; Le Corvec et al ., ]. Local magmatic stress fields: Emplacement of dikes and sills below volcanic centers results in the formation of pressurized magma chambers and cylindrical conduits that can locally perturb the regional stress field [ Muller and Pollard , ; Gudmundsson , ; Bistacchi et al ., ; Muirhead et al ., ] (Supporting information text S1). In these instances, high magma pressures locally rotate the principal stress directions, resulting in the formation of cone sheets and/or radial dike intrusions [ Muller and Pollard , ; Gudmundsson , ; Airoldi et al ., ]. Volcano edifice loading: Radial diking can also be promoted by stress perturbations related to the load of an overlying volcanic edifice [ Pinel and Jaupart , ; Hurwitz et al ., ; Roman and Jaupart , ; Le Corvec et al ., ]. Rift segment interactions: The regional stress field can be locally perturbed by the mechanical interaction of adjacent rifts and en echelon faults and fracture segments [ Pollard and Aydin , : Olson and Pollard , ; Morewood and Roberts , ; Tentler , ] (supporting information text S2). Within the interaction zone between structural segments (i.e., transfer zones), principal stresses rotate to produce faults and dikes exhibiting rift‐oblique trends that act to link rift segments (e.g., the Okataina Domain of the Taupo Volcanic Zone, New Zealand) [ Rowland and Sibson , ].…”

Numerical modelling of triple-junction tectonics at Karlıova, Eastern Turkey, with implications for regional magma transport

“…However, some chambers reach depths of 7-9 km, depending on the tectonic regime and crustal structure, and may also be regarded as comparatively shallow (Chaussard and Amelung, 2014). Chambers at greater depths are normally classified as deepseated reservoirs, and these may reach depths of 20-30 km or more (Gudmundsson, 2012;Chaussard and Amelung, 2014;Le Corvec et al, 2015).…”

“…The conditions for magma-chamber rupture and dyke injection have been analysed by many (e.g. Gudmundsson, 1990Gudmundsson, , 2006Grosfils, 2007;Hurwitz et al, 2009;Gerbault, 2012;Le Corvec et al, 2015). Many of the basic ideas are reviewed and analysed by Gudmundsson (2012), with particular reference to direct observations of fossil magma chambers and the results of hydraulic fracture stress measurements in drill-holes worldwide down to crustal depths of about 9 km.…”

A review of laboratory and numerical modelling in volcanology

“…Such bubble plumes could impact magma mixing within the chamber and the stability of the magma chamber; they could also have the potential to trigger an eruption and could affect the style of eruptive activity. Magma contamination from roof and wall melting has also been studied experimentally (Leitch, 2004).…”

“…Galgana et al, 2013) or by including mechanical heterogeneity and a stiffness contrast between crust and mantle (e.g. Le Corvec et al, 2015). Interactions between a phenomenon and its surroundings are commonly accounted for in numerical models by simplified coefficients; for example, the entrainment of ambient air into a rising plume is described by two entrainment parameters: one considers radial entrainment due to turbulent eddies at the plume edge, and the other accounts for entrainment due to the effects of wind on the plume.…”