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Numerical modeling of segregation and differentiation in partially melting orogenic crust

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Date Limite Candidature : lundi 11 juillet 2022

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General information

Reference : UMR5563-MURGER-001
Workplace : TOULOUSE
Date of publication : Monday, June 20, 2022
Scientific Responsible name : Muriel Gerbault
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Application requirements : The application should include a CV, documentation of educational merits, qualifications and previous activities. Skills in computational programming and in petrological thermodynamics are most required. A letter detailing personal motivations and a proposition accompanying the research program. If you have completed a degree abroad, it will be assessed by the doctoral school SDU2E before employment can take place.
Project summary: The aim is to develop a numerical coupling approach of thermodynamic and thermomechanical tools involved in the genesis of a partially melting crust and liquid/solid segregation, to bridge the gap between our understanding of the mineral scale metamorphic reactions and the crustal scale gravitationally driven viscous flow in response to external forces. This project pursues the development of OpenFOAM VOF solvers that were shown to track well crustal scale flowing heterogeneity interfaces (Louis-Napoleon et al., 2020, 2021). The incorporation of thermal and compositional interactions between distinct fluid phases will allow to investigate how these fluid phases evolve, migrate, and contribute to the entire crustal segregation balance.

Aim and objectives : Crustal differentiation is controlled by partial melting and magma fluid transfers (Sawyer, 1994). In this context, the circulation of fluids has a decisive impact on the transfer of elements of economic interest (Chi & Xue, 2011). Understanding these processes is therefore essential to guide exploration and exploitation of subsoil resources. While the conditions for partial melting and crystallization are generally determined from thermodynamic modeling (Holland & Powell, 2011), the dynamic behavior of partially melting crusts is also approached by thermo-mechanical modeling (Poh et al., 2020; Piccolo et al., 2021; Schmeling et al., 2021). Some models take into account fluid-generating metamorphic reactions at the large scale, while others target segregation processes at the grain scale (Petrella et al., 2021): our objective here is to link these scales with the support of field observation and laboratory petrology measurements. While research communities argue about the flow modes of magmatic fluids (eg. migration, mixing or reactive transport) and whether melt columns are chemically open systems at distinct depths (eg. Cornet et al., 2022), here we will seek to further formalize such processes at the intermediate scale.
Our main field target is the Eburnean belt of West Africa, which testifies of a major crustal growth event between 2.0-2.2 Ga, and is composed of volcano-sedimentary series affected by greenschist metamorphism, of granulites and intruded plutons. This belt is characterized by 10-30 km wavelength alternations between greenstone belts, in a metamorphic gradient of about 30-40°C/km. While a dominant role of gravitational instabilities was proposed (Vidal et al., 2009) other studies rather favor thr role of horizontal motion (Baratoux et al., 2011). The WAXI program (waxi4.org/waxi-4/waxi-1-3/) has gathered a unique database that highlights the role of the volcano-sedimentary metamorphism in the genesis of migmatitic gneisses, plutons and their associated mineral resources (Masurel et al., 2021; Bonzi et al., 2021). Other targets will also serve as comparison: the Australian proterozoic terranes, the cretaceous European Alps and Naxos's migmatite domes (Siebenaller et al., 2013). Field and laboratory data will be used first to constrain the initial and limiting conditions of the models and guide the identification of major fluid transport modes (reaction, diffusion, localised, diapirism, convection), whereas the models in turn, will help seeking on the field, for the characteristics of « homogeneisation/segregation» processes. This merging of disciplines fosters in the context of the IRN FalCol french-australian network (oceania.cnrs.fr/project/irn-falcol/).
The VOF numerical method is one of the best that conserve mass in multiphasic fluid flow, which is a major issue when understanding crustal segregation processes. The aim of this project is to pursue the development of solvers embedded in the opensource code OpenFOAM, by incorporating the thermodynamic evolution of heterogeneous rock mass (e.g. adapt MagmaFOAM, Brogi et al.,2020; and Carrillo et al., 2020). This control on compositions and rheologies of the matrix and liquids will help us identify the different scales of transport of fluid volumes (percolation via the porous medium or by convection-diapirism), and their impact on solid/liquid segregation. Particular attention will be dedicated to partial melting and crystallization reactions which play a role in the cycle of aqueous and carbonic fluids participating in metallogenic processes (Petrella et al., 2021).
Work plan
* Year 1 : hands on OpenFOAM (https://openfoam.com) starting at the crustal scale (same setup as
Louis-Napoleon et al., 2021), varying initial conditions and merging with thermodynamic
conditions. Coding and publication 1 draft.
* Year 2 : Numerical implementation of a multiphysics solver for the 0.1-100 meters scale.
Field work within the Falcol IRN network. 1 workshop or international conference.
* Year 3 : Results analysis, synthesis, and draft publication 2, conference participation. PhD ms. writing.
Resources
* Equipment : analytical platforms for petrological and geochronology analyses at GET (www.get.omp.eu/plateformes/pole-petrologie-et-mineralogie/), as well as the numerical equipment of the community cluster Nuwa (www.aero.obs-mip.fr/parc-instru/platmod/) and the Olympe supercomputer from the CALMIP regional mesocenter (www.calmip.univ-toulouse.fr/).
* Fieldwork, traveling, and conferences expenses will be supplied for with national yearly grants.
Bibliography
Brogi, F., Colucci, S., Matrone, et al. (2022). MagmaFOAM-1.0: a modular framework for the simulation of magmatic systems. Geoscientific Model Development, 15(9), 3773-3796.
Louis-Napoléon A., Gerbault M., Bonometti T., et al. (2020). 3D numerical modelling of crustal polydiapirs with volume-of-fluid methods. Geoph.J.Int. 222(1) 474-506.
Louis-Napoleon A., Bonometti T., Gerbault M., et al. (2022). Models of convection and segregation in heterogeneous partially molten crustal roots with a VOF method--I: flow regimes, GJInt , 2022.
Petrella, L., Thébaud, N., Evans, K., LaFlamme, C., & Occhipinti, S. (2021). The role of competitive fluid-rock interaction processes in the formation of high-grade gold deposits. Geochimica et Cosmochimica Acta, 313, 38-54.
Piccolo, A., Kaus, B. J., White, et al. (2020). Plume—Lid interactions during the Archean and implications for the generation of early continental terranes. Gondwana Research, 88, 150-168.
Poh, J., Yamato, P., Duretz, T., et al. (2021). Transition from ancient to modern-style tectonics: insights from lithosphere dynamics modelling in compressional regimes. Gondwana Res. 99, 77-92.
Siebenaller, L., Boiron, M., Vanderhaeghe, O., Hibsch, C., Jessell, M. et al. (2013). Fluid record of rock exhumation across the brittle–ductile transition during Metamorphic Core Complex formation (Naxos Island). J. Metam.Geol. 31(3), 313-338.

Work Context

The GET (Geosciences Environnement Toulouse) is a multi-disciplinary research laboratory in Earth and Environmental Sciences attached to the Midi-Pyrenees Observatory (OMP). It is as so-called mixed unit (CNRS, IRD, P. Sabatier University, CNES) that brings together about 226 people.
The research themes are complementary and include studies of the internal Earth, its surfaces and continental interfaces, to improve knowledge on (i) the evolution and dynamics of the Earth, (ii) spatial and in situ observation of the Earth, (iii) the critical zone and fluid-rock-living interactions, and (iv) georesources and Contaminants-Environment-Health interactions.
This PhD will take place within the TIL team (Terre Interne Lithosphere), which specifically studies the dynamics of the Inner Earth, generally from a petrological point of view.
It will also be co-supervised by:
i) Nicolas Thébaud, researcher in Australia and a geologist specialist in the metalogenic (and metamorphic) provinces of Australia and Africa, and
ii) Thomas Bonometti and collaborators of the IMFT (Institute of Fluid Mechanics, Toulouse), experts in modeling fluid media and with the numerical code OpenFoam.

Constraints and risks

No specific constraints apart from those rising from using computers.
The candidate may be proposed to participate to a field work mission in isolated environment.

Additional Information

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