Evolution of large Venusian volcanoes: Insights from coupled models of lithospheric flexure and magma reservoir pressurization

Abstract

[1] The growth and evolution of large volcanic edifices on Venus should reflect interactions between local magma reservoir-induced stresses and broader-scale stresses resulting from flexure of the lithosphere beneath the edifice load. Here, we explore the relationship between magma movement in the lithosphere and the flexural stress state via static, gravitationally loaded, axisymmetric finite element models. We find that reservoirs situated in the lower (extensional) lithosphere fail at the bottom and are therefore not viable long-term conduits for upward magma transport. Furthermore, for high-stress conditions (e.g., large edifices or thin lithospheres), chambers in the lowermost lithosphere exceed the failure criterion even before pressurization and are therefore unstable. In contrast, magma chambers located in the upper (compressional) lithosphere fail at or somewhat above the reservoir midsection, promoting lateral sill injection; continued failure in this mode would tend to produce oblate magma chambers with zones of intrusion at their margins. Reservoirs near the flexural neutral plane require the greatest overpressure to reach failure, emplacing cone sheets that transition to sills further from the chamber. The out-of-plane orientation of principal extensional stresses in the flexed lower lithosphere predicts the presence of radial dikes that are likely the main conduits for any subsequent magma ascent from the mantle melt source region. Our results also explain how the evolving stress state in the lithosphere tends to redirect magma passage over time: magma ascending into the lithosphere beneath the edifice is diverted to lateral sills in the upper lithosphere, inhibiting summit eruptions and possibly shifting eruption locations to the lower flanks at and beyond the distal margins of an oblate chamber or sill complex. We apply these results to interpret the observed structure and tectonism of Sapas Mons, Venus, in terms of flexurally controlled intrusive processes.Citation: Galgana, G. A., P. J. McGovern, and E. B. Grosfils (2011), Evolution of large Venusian volcanoes: Insights from coupled models of lithospheric flexure and magma reservoir pressurization,

Correlation Between Graben Orientation, Channel Direction Change, and Tectonic Loading: The Elysium Province, Mars

“…The shallow magma chamber (Figure f) shows a forebulge maximum at twice the edifice radius from the edifice axis with a distinguishable maximum, similar to Comer et al (), and the forebulge predicted for the deeper magma chamber is beyond the two‐radius limit with little bulge visible. We propose that a shallower magma chamber and/or a smaller T e produce a more pronounced forebulge since they have greater influence on the lithosphere upper boundary, which is consistent with the models of Grosfils (), Hurwitz et al (), Galgana et al (), and Galgana et al ().…”

“…Hurwitz et al () expanded the model to include the impact of edifice growth on chamber rupture behavior and predicted the blocking of magma ascent and magma flow re‐routing to radial flow on edifice mass increase. Galgana et al () incorporated the effects of lithospheric flexure into the model and Bistacchi extended the rheological behavior and demonstrated correlation between the model (Bistacchi et al, ) and the distribution of cone sheets and dikes in the Cullen Igneous Province. Most recently, Galgana et al () modeled the effects of uplift on magma chamber rupture constraining the temporal and cyclic aspects of eruption and uplift and the conditions for inhibiting magma ascent and diversion to radial flow.…”

The influence of lithospheric flexure on magma ascent at large volcanoes on Venus

“…The effects of stresses from lithospheric flexure on magma chamber failure and dike propagation at large volcanoes on Venus were demonstrated by Galgana et al . [, ].…”

Pressure conditions for shear and tensile failure around a circular magma chamber; insight from elasto-plastic modelling

“…In addition, deformation is also governed by the rheology of the magma, temperature and viscosity of the bedrock, the driving pressure, stresses resulting from the intrusion itself, dynamic fluid transport through the chamber and the bedrock, and many other temporally and spatially variable factors discussed elsewhere in the literature (e.g. Anderson, 1936;Rubin and Pollard, 1987;Lister and Kerr, 1991;Rubin, 1995;Day, 1996;Fialko et al, 2001;Hurwitz et al, 2009;Karlstrom et al, 2010, Galgana et al, 2011, de Saint Blanquat et al, 2011. Our near future perspectives are to improve the modeling of coupled hydromechanics (Gerbault et al, in prep.…”