Petrology and Geodynamics

Research

Our research interests lie on better understanding changes of physical rock properties in relation with their metamorphic evolution. Our  approach to these questions ranges from the microscopic scale such relation between deformation and minerals growth up to large orogen scale, e.g. effect of rheology changes according to phase transition on geodynamic processes (e.g. mountain building, passive margin formation...).

Our research activity focuses, until now, on the following themes:

 

Field studies

Field studies are a crucial part of our research, as a base to describe, understand, and quantify geological processes. I am focusing on the following topics:

  • Metasediments in subduction zones: In contrast to mafic complexes or meta-igneous rocks, metasediments commonly crop out continuously over very large areas in many mountain belts. Since these meta-sediments cover large areas, this allows to simultaneously observe their structural and metamorphic evolution, and thus to decipher the geodynamic frame (Alps, Turkey, Sistan, Southern Apennine). By dating the different stages of the evolution, I was able to describe the internal dynamic (accretion and exhumation) of the paleo-accretionary prisms.
  • Subduction-collision processes: The subduction-collision transition is a critical stage for the building of mature orogens. During this event, the whole dynamic of the system is changing: the type of accreted material in the orogenic wedge (from oceanic sediments to crustal rocks), mode of accretion the thermal regime (from franciscan to barrovian gradient), the rheology of the subducting lithosphere (numerous slab break-off appear at that stage). Description and quantification of the different changes are crucial to understand processes acting during this transition. By petrological and dating methods associated to structural studies, 3D thermal and rheological properties can be well documented (Alps, South Anatolia).
  • Margin formation: Early stages of continental thinning, during which major thermal changes occur indicated by formation of LP granulitic lower crust, mantle-related melting or intrusions of ultramafic bodies into the lower density continental crust, are still not well known. By studying the evolution of the crust-mantle boundary thermal state from metamorphic and magmatic activities in different areas (Alps, Apennines, Morocco), I propose to establish a relation in the evolution between deep crust and basin deposits.
  • Evolution of cratons: Geodynamic reconstructions of ancient belts are extremely important for understanding the development of ore deposits, particularly those associated with metal-concentration systems that involve parts of the lower crust and mantle. The formation of many types of epigenetic ore deposits involves some form of control by fluid production during metamorphic processes and by structures produced during crustal deformation. However, in many place this geodynamic evolution is only constrained by magmatic events. The understanding of the formation of ore deposits is intimately dependent not only on the description of the fluid composition, but also on the understanding of the tectono-metamorphic evolution of the rocks hosting the ore deposits (Morocco, Iran).

 

Quantify and modelling rock properties changes

  • The scaling of rock properties under transient conditions is rather unknown. It is therefore one of the greatest challenges in Earth sciences to quantitatively understand a) the influence of transient conditions on physical properties, b) the scaling of equilibrium material properties from atomistic scale up to global scale, and c) to better understand the meaning of geophysical signals (seismic, tomography, gravity…) . 
  • To develop realistic process modeling approaches the spatial and temporal variability of the corresponding governing material properties are needed i.e. a links between material properties and geophysical signals have to be established. Petrological and thermodynamical approaches allow to investigate and quantify the changes of physical properties of rocks such as density, volume, seismic velocities, rheology according to large range of pressure, temperature, chemical composition and hydration degree (e.g. different rock types).

 

Numerical modeling of Geodynamic processes

  • Subduction processes: During the past decades, mainly the equilibrium properties of geomaterials had been studied. However, the processes such as dehydration reactions and kinetically hindered phase transformations which may trigger earthquakes at different depths; fluid flow, varying stress regimes due to active tectonics which can lead to a significant change in physical properties with a complex feedback to tectonics and geodynamics.
    Dehydration reactions during metamorphism in subduction zones represent a substantial source of fluid. Using thermodynamic modeling we investigate the parameters that control fluid production in the forearc wedge and in the slab and the relation on subduction dynamics (change of the slab-pull, localization of earthquakes, effect on the rheology of the mantle wedge. The amount of released fluids is quantified by dynamic modeling according to the thermal structure of the subduction as well the rocks type.
  • Plateau evolution: The interplay between the dominant denudation conditions and the rheology of the lithosphere, both well documented by erosion rates and processes can provide significant constraints on deep processes of plateau building. I am developing a model to quantify the contribution of mantle-crust interactions into plateau building for two different geodynamic settings, the East African and the East-Anatolian Plateau.  The contribution of these interactions on plateau building can be estimated and quantified by the thermo-mechanical evolution of different geodynamic settings and uplift scenarios by taking into account changes of physical properties of rocks as modeled from petrology.
  • Margin formation: The continental crust thinning and the genesis of so-called passive continental margins are usually explained by models using pure stretching, simple shear or combination of both models. And the subsidence is assumed to be a consequence of thermal relaxation of the lithosphere. In order to take into account effect of thermal changes (formation of granulites, intrusion of magma...) on the crust rheology on the subsidence processes for the different types of passive margin, I am developing numerical models of rifting processes including changes of physical properties associated to the thermal evolution