Annuaire

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©Andréa Tommasi

Andréa TOMMASI

Fonction : Chercheur

Thème de recherche principal : Déformation

Équipe(s) : MI - Manteau et Interfaces

Localisation : Bt22 416

Téléphone : +33 (0)4 67 14 49 12

E-mail :

My research themes couple geodynamics and petrophysics:

  • the relations between mantle flow and the anisotropy of its physical properties, mainly based on: (1) multi-scale numerical models of the development of olivine crystalographic orientations and prediction of the associated seismic and viscous anisotropy in the upper mantle, transition zone, and D » layer (seminar presented at the Flow in the deep mantle workshop at College de France in December 2016), (2) the caracterisation (by the analysis of mantle samples) of the seismic anisotropy associated with the deformation of the lithospheric (and sublithospheric) mantle in continental collision zones, rifts, subductions, and lithospheric-scale shear zones. In the past, I have also worked on the relation between deformation and the anisotropy of electrical conductivity in the upper mantle inferred from long-period MT measurements and numerical models and experimental measurements of the anisotropy of thermal diffusivity in the upper mantle. The most recent work focuses, however, on how development and preservation of viscous anisotropy in the lithospheric mantle leads to memory effects in plate tectonics, that is, reactivation of ancient plate boundaries and translithospheric shear zones hundreds of m.y. after their formation.
  • the feedbacks between deformation and fluids or melts in the mantle by analysing natural systems and trying to unravel  the relations between reactive melt percolation leading to refertilization and deformation (in the Lherz peridotite, Ronda, the Ethiopian rift…), document deformation-induced melt segregation in Oman and Lanzo or the effects of hydrous melts and crystallization of hydrous phases on the peridotites’ rheology in Finero. Examples of some of these studies are presented in the seminars given in the Melts in the Mantle program at Cambridge in 2016: Feedbacks between deformation and melts in the upper mantle & How do melts change texture and anisotropy of mantle rocks
  • the interactions between plate tectonics and mantle convection – this question was central to the two EU training networks I coordinated. First, CRYSTAL2PLATE (2009-2023)n  which associated 7 European research teams internationally recognized for their excellence in in Geodynamics, Petrophysics, Geochemistry, Petrology, Fluid Mechanics and Seismology to study the interactions between lithospheric plates and the convecting mantle. CRYSTAL2PLATE trained 10 PhD students and 2 postdocs on projects focusing on various aspects of the question: How does plate tectonics actually work? by studying the interactions between lithospheric plates and the convecting mantle and analyzing (1) how plates modify or are affected by convection, (2) the role of the preexisting structure of the plates on the deformation distribution, (3) the coupling between chemical and physical processes at various scales in the mantle. These studies led to the publication of >20 articles (see the project publications list). Then,  CREEP (Complex RhEologies in Earth and industrial Processes) (2015-2019) associated 10 European research teams and 10 industrial partners to provide training to 16 early stage researchers  via a cross-disciplinary collaborative research program focused on the complex mechanical behaviour of Earth materials and their implications for geodynamic or industrial processes. The 16 PhD projects covered a large spectra of applications of complex rheologies, from the deformation of the Earth surface and deep layers, to geothermal and petroleum exploration or industrial processes (see the project publications list).
  • the elementary processes resulting in strain heterogeneity and controlling recrystallization during viscoplastic (ductile) deformation. In the frame of the ANR DREAM (2014-2018) we associated in-situ characterization by EBSD of the microstructure and texture (CPO) evolution during annealing and deformation experiments in the SEM Crystal Probe on analog materials (hexagonal ice and magnesium polycrystals) and numerical modelling of the viscoplastic deformation heterogeneity and of the recrystallization processes at the crystal and aggregate scales. This study is carried in collaboration with colleagues from Glaciology (IGE Grenoble) and Materials Sciences (LEM3 Metz et CEMEF Sophia-Antipolis). This subject was also at the center of the activities of the CNRS INSIS-INSU Groupement de Recherches (GDR) Recristallisation et croissance des grains (2011-2015 & 2017-2021), which reunited academic and industrial researchers working on recrystallization phenomena from the Material and Earth Sciences communities in France.
  • the role of micro-scale dependent, time- and space-evolving rheologies on generating strain localization in the Earth. The ERC Advanced RhEoVOLUTION, which I coordinate since November 2020, proposes a « revolution » in how we define rheology (the equations relating forces to deformation) in geodynamical models. It aims at predicting the onset and evolution of strain localization and postulates that modeling spontaneous ductile strain localization has been impossible so far, because this strain localization depends on processes active at the mm scale, which cannot be explicitly simulated in geodynamical models. The tools we designed and propose to develop in RhEoVOLUTION will make it possible by bridging scales and modelling how heterogeneity and anisotropy in the mechanical behavior of rocks control strain localization from the cm to the tens of km scale in the Earth. To do so, we will: 1. describe the heterogeneity of mechanical behavior of rocks deforming by dislocation creep by stochastic parameterizations of the rheology; 2. constrain these parameterizations using experiments with in-situ follow-up of the microstructure and strain evolution; 3. accelerate by orders of magnitude the calculation of the evolution of mechanical anisotropy during deformation using supervised machine-learning; 4. quantify feedbacks between the main processes producing strain localization by comparing the predictions of models parameterized to simulate these processes to observations in natural shear zones. For a brief introduction on points 1 and 2 see the talk given at the CIG workshop on Strain Localization in July 27th, 2020.
  • In addition, in a not so far away past (at least I would like to believe!), I have also worked on: (1) the effect of thermally-induced large-scale intraplate rheological heterogeneities (cratons, basins) on the mechanical behavior of a continental plate submitted to compression (continental collision) through the analysis of field examples (Neoproterozoic collisional belts of Brazil) and finite-element models; (2) the feedbacks between magmatism and deformation in the continental crust: coupling between granites emplacement and development of lithospheric scale strike-slip shear zones; and (3)  the partioning of the deformation in continental collisional belts: kinematic analysis of a neoproterozoic collisional belt of southern Brazil (field mapping and microstructural studies) showing a temporal and spatial partitioning of the deformation between tangential and strike-slip shear zones.

Publications

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