Bonjour à tous,
Le prochain VolcaPot sera organisé le mardi 21 juin à 11h dans la salle de séminaire du LMV. Nous aurons le plaisir d’assister à la présentation de Nicolas Le Corvec, post-doctorant au laboratoire, qui nous présentera ses travaux :
Effects of mechanical, rheological and tectonic controls on the formation of giant radial dike systems on Venus: Insights from finite element modeling.
Radial dike systems are intriguing magmato-tectonic features occurring on Venus, Earth and Mars. For such systems to form, massive quantities of magma ascending from the mantle must be redirected laterally at shallow depths within the lithosphere over several hundred kilometers. Observations have shown different patterns from continuous fanning to subswarms of subparallel dikes. As magma ascends towards the surface, accumulation in reservoirs situated at various depths within the lithosphere is often coupled with the growth of a volcanic edifice at the surface. The stability of magma reservoirs, and therefore the generation of magmatic intrusions, is influenced by their shape, their location, the tectonic environment and the mechanical and rheological properties of the lithosphere. Based on previous work investigating the role of flexure on the stability of magma reservoirs, we developed new models to test: 1- the role of a mechanically-layered lithosphere; 2- the role of extensional stresses; and 3- the ellipticity of magmatic reservoirs on the formation of these radial dike systems. To explore these scenarios, we used the COMSOL Multiphysics finite element package allowing us to develop: 1- 2D axisymmetric elastic models made of mantle and crustal components; 2- 3D elastic models in which an extensional stress was applied; and 3- elliptical magmatic reservoirs embedded within 2D axisymmetric elastoplastic models. Different tectonic environments were studied: lithostatic, upward flexure due to uplift consistent with a plume-derived origin and downward flexure due to the load of a volcanic edifice. Mechanical layering within the lithosphere impacts the location of failure along a magmatic reservoir and the type of magmatic intrusions. We observe that shallow magma reservoirs in an upward flexure environment tend to produce radial dikes. Regional Extensional stresses in 3D tend to focus the location of failure along the magma reservoir, therefore limiting the formation of continuous fanning pattern. Finally, the elliptical shape of a magma reservoir favors continued expansion and increasing ellipticity, because failure at the midsection requires less overpressure as the ellipticity of the reservoir increases. These results highlight new physical and structural controls on the formation of radial dike systems on Venus. Specifically, we can infer 1- potential crust/mantle ratios within the Venusian lithosphere; 2- the extensional stress regime linked to the formation of specific radial dike systems; and 3- the mechanisms of magma chamber growth linked to the formation of calderae observed in conjunction with radial dike systems on Venus.
(Tradition oblige, quelques victuailles vous accompagnerons jusqu’à l’heure de l’apéro)