Description du sujet de thèse

Seafloor spreading is a key process of plate tectonics that shapes two-thirds of the Earth's surface. In addition to tectonic faulting, it involves the intrusion of dikes along the axis of mid-ocean ridges, which are sourced from shallow lenticular reservoirs that form at the top of magmatic mush zones. The aim of this thesis is to explain how these reservoirs may spontaneously pressurize, triggering uplift of the seafloor and deformation of the axial lithosphere, potentially leading to an eruption.
The PhD student will study the dynamics of decompaction of a two-phase medium (solid-magma), representing the partially-molten zone of a ridge axis, and its interaction with the overlying elastic lithosphere. His/Her work will focus on understanding how magma buoyancy, as well as mush permeability and rheology, condition the development of magmatic overpressure. The thesis will involve the development of analytical and numerical models of increasing complexity, enabling us to explore the effect of different rheologies on the magma-solid two-phase medium: from Newtonian viscous to visco-elasto-plastic and granular-type behavior. The models will be constrained by geodetic observations of seafloor uplift at the axis of various ridges where magmatic plumbing has been imaged by seismic methods.

References:

Sinton, J.M., and Detrick, R.S., Mid-ocean ridge magma chambers, J. Geophys. Res., 97, 1992

Kelemen, P., and Aharonov, E., Periodic formation of magma fractures and generation of layered gabbros in the lower crust beneath oceanic spreading ridges, Geoph. Monog. Ser., 1998

Katz, R.F., The dynamics of partially molten rock, Princeton University Press, 2019

Carbotte, S.M., Arnulf, A., Spiegelman, M., Lee, M., Harding, A., Kent, G., Canales, J.-P., and Nedimović, M., Stacked sills forming a deep melt-mush feeder conduit beneath Axial Seamount. Geology, 48, 2020

Contexte de travail

The PhD student will be employed by CNRS (Délégation Paris Centre), and enrolled in the Geosciences, Natural Resources and Environment doctoral school (GRNE, ED 398). The PhD will be carried out within Ecole Normale Supérieure's Geology Laboratory, a joint research unit bringing together CNRS researchers and ENS-PSL faculty members. The successful candidate will join the Deformation and Structures team, which specializes in the observation and modeling of tectonic processes, from grain to lithospheric scale, and from seismic cycles to the growth of major geological structures. The PhD will be carried out under the supervision of Jean-Arthur Olive and Javier Escartín, as part of ERC project SeaSALT (Seafloor Spreading on Short And Long time scales, PI: J.-A. Olive), which involves the recruitment of several PhD students and post-docs working on different aspects of seafloor spreading (magmatism, tectonics, hydrothermalism) on a range of time scales. The PhD student will also benefit from a network of national and international collaborations to support the development of numerical models, and their comparison with observations of active deformation at mid-ocean ridges.

Applicants should hold a Master's degree (or equivalent) in Geophysics, Physics, Geology (or related field) and have a strong interest in physical volcanology, geodynamics and fluid/solid mechanics. Experience with computational fluid or solid mechanics, or numerical geodynamic modeling would be ideal. Proficiency in English is necessary.
Interested candidates are invited to send a statement describing their background and specific interest in the project, a CV and the contact information of academic references to the project PI.