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Géodynamique

Our primary objective is to understand the past and present dynamics of the interior of the Earth and other planets. The dynamics of the Mantle, Core and Inner Core of the Earth have different features, yet they are intricately connected through heat and mass exchanges.

Typical questions under investigation are, for example:
- the question of the emergence and sustainability of plate tectonics on Earth;
- Crystallization of the early Mantle and long-term existence of a Basal Magma Ocean;
- Dynamics of the inner core, compatible with seismic anisotropy and hemispherical asymmetry;
- Accretion/differenciation of the Earth.

We develop mathematical models of stability of fluid motion, nonlinear evolution, inversion or assimilation techniques. We then solve discretized versions of these models on local, regional or national clusters. We also run experiments of fluid mechanics and/or crystallization.

In our group, the term "dynamics" must be understood in a broad sense: it should rather be "thermodynamics" as temperature effects and heat transfer are prominent features in planetary interiors. Secondly, mineralogy and geochemistry play a crucial role on the rheology, thermal conductivity and other transport properties, and have to be included in our analyses. In addition, seismology and geology of the lithosphere provide observational constraints which play a key role in our research. 

 

Researchers


Thierry ALBOUSSIERE (DR)

My research interests are covering different aspects of planetary dynamics: the dynamo effect in the Earth's core, dynamics and thermodynamics of the inner core, of the early mantle and compressible convection. Using analogue experiments and numerical modelling, I have been studying crystallization processes in the dendritic regime, with applications to the crystallization of the inner core (PhD of Ludovic Huguet, collaboration with Michael Bergman). In particular, with Renaud Deguen, we have identified a mechanism of convective translation of the inner core, as a result of the interaction between phase change, heat transfer in the outer core, convection in the inner core and self-gravitational equilibrium. We are working on a similar dynamics for the early mantle crystallization with Stephane Labrosse and Adrien Morison. More recently, my research has been focused essentially on compressible effects in convection. With Remi Menaut (PhD), we are investigating experimental compressible effects in a centrifuge. Increased gravity is also accompanied by Coriolis effects (PhD of Yoann Corre). I am also interested in theoretical aspects of compressible convection: with Yanick Ricard, we have analyzed different equivalent expressions for the viscous dissipation and we have performed a comprehensive stability analysis of compressible convection, valid for any physically sound equation of state. With Stephane Labrosse, Yanick Ricard and Jezabel Curbelo (Spanish collaboration), we are analyzing numerical compressible convection with different approximation levels, from an "exact model" (Navier-Stokes, equation of state, entropy equation) to a Boussinesq solution, with intermediate anelastic models.

 

Nicolas COLTICE (Pr)

I am a geodynamicist using numerical modelling to bridge theoretical models with observations. I had the chance to explore various fields of geosciences, from geochemistry of the carbon cycle, to sedimentology of Archean basins, or global tectonics. These past years, I have been focused on the AUGURY project (www.augury.eu), which aims at building inverse methods to realise tectonic reconstructions. The particularity of the approach is our use of  convection models producing plate-like behaviour self-consistently. We develop data assimilation codes (sequential and variational) starting from the code StagYY initiated by Paul J. Tackley (ETH Zurich), and using the data base of the EarthByte group in Sydney.

 

Stéphane LABROSSE (Pr)

My research focuses on the dynamics and evolution of the deep Earth from its earliest stages to recent times, with a particular focus on the thermal evolution. This includes modelling of the thermal and chemical evolution of the core, inner core growth,  mantle convection. In the recent years, I have focused more on processes related to the early deep Earth: core formation, magma ocean dynamics and evolution, solid mantle convection interacting with magma oceans. I address these issues mostly using thermodynamics and theoretical and numerical models of fluid dynamics.
 

Frédéric CHAMBAT (MCF)

These past years, with Yanick Ricard, Renaud Deguen et al., we have been considering fluids crossing a zone of rapid density change, so thin that they can be considered as a density jump interface. For a Newtonian viscous fluid with low Reynolds number that keeps its rheological properties within the interface, we have shown that the traction cannot be continuous across the density jump because the tangential stress is singular. The appropriate jump conditions have been established and we are implementing them in convection codes.  With Nicolas Rambaux et al., we investigate the hydrostatic shape and gravitational potential coefficients of self-gravitating and rotating bodies large enough to have undergone internal differentiation and chemical stratification. The main purpose is to develop the reference hydrostatic shape for relatively fast rotating bodies up to third order to reach an sufficient accuracy to interpret the global gravity and shape observations of various space missions (on large asteroids, dwarf planets and TNO).  My third main research theme is history of sciences, especially the critical edition of D’Alembert's complete works : I am the editor of the 'Reflexions sur la cause générale des vents' (1747), a work on the dynamics of atmosphere and oceans due to the lunar and solar tides.

 

Post Doctorates


Roberto AGRUSTA (Post doc)

My research focuses on the dynamic of the lithosphere and mantle. I make use of numerical modelling tools to investigate mantle convection in relationship to its static and dynamic physical proprieties. My personal area of expertise is related to study the interaction between sinking plate and mantle transition zone. My leading interest include to understand what drives and resists plate to sink through or to stagnate in the mantle transition zone, which are the plausible mechanisms to change the slab dynamic, and how the slab-transition zone interaction might have changed through Erath’s history. My recent research focuses on the evolution of mantle convection during magna ocean crystallization to look at the feedback associated with the evolution of the solid/liquid phase change between the solid mantle and the magma ocean(s).

 

Mélanie GERAULT (Post doc)

I am interested in how the interactions between the lithosphere and the mantle shape the Earth's surface. I work with numerical models to understand the mecanisms behind plate velocities and lithospheric stresses, including the formation of topography. One of my projects aims at better understanding the net rotation of the lithosphere with respect to the lower mantle using 3D spherical models where plate boundaries evolve self-consistently (in collaboration with Nicolas Coltice). My other project aims at coupling a 2D geodynamic code with a Markov chain Monte Carlo approach in order to determine the physical properties of the Mexican subduction zone, where the subduction is flat and a large earthquake recently occurred (in collaboration with Thomas Bodin).

Students


Adrien MORISON (Phd)

I am working on the dynamics of the primitive Earth mantle. Due to the heat brought by impacts, radiogenic heating, and core differentiation, the primitive mantle may have been totally melted, forming a magma ocean. Depending on the temperature profile and the shape of the solidus in this magma ocean, the crystallization of the solid mantle may have started from the bottom or the middle of the magma ocean. This leads to the formation of a solid spherical shell with magma oceans above and/or below. Convecting matter in the solid shell can cross the boundary between the solid shell and the magma ocean by melting and freezing. This phenomenon is parametrized with a boundary condition applied to the creeping flow in the solid. I study the effects of this boundary condition on the convection in the solid.

 

Stagiaire


Victor LHERM

My research focuses on the formation and the differentiation of the Earth's core. During planetary accretion, multi-sized impactors supplied energy and material to the growing planet, from the initially small planetesimals to the giant impacts involving planet embryos. The latest accretion stages, resulting in the formation of the Moon, involved colliding differentiated bodies with an iron core surrounded by silicates. These impacts are likely to produce magma oceans in which thermochemical equilibration of the impactors occurs. In order to interpret geochemical data in term of accretion timing and conditions, the degree of heat partitioning and chemical fractionation have to be examined. For that purpose, I perform numerical simulations and laboratory experiments to study deformation, fragmentation and mixing processes involved during the equilibration of impactors' cores.