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Dynamics of continental deformation : from rifting to collision

Continental deformation is subject to first-order geodynamic forcing from an internal source. It can be deciphered and studied on the Earth surface through preserved structural objects, via the exhumation/erosion relationships of raised massifs and, at last, from the deposits in the associated subsiding basins. Our approach, which aims to address and constrain the dynamics of these deformations, is focused on the following tasks : (i) quantify the history of individual objects or markers, such as terraces and fault scarps (structure and cosmogenic dating of surfaces) ; (ii) understand the dynamics of the exhumation of massifs (low-T thermochronology and cosmogenic erosion rates) ; or (iii) reconstruct mountain range evolution from sedimentary archives (sedimentology, magnetostratigraphy, detrital thermochronology, and geochemical tracing). Thanks to several remarkable natural laboratories (Pyrennees, Tianshan, Himalaya, Afar, Greece...) our groups will study various geodynamic processes as presented below.

From continental collision to the evolution of orogenic plateau

The deformation process of the continental crust in convergent areas remains highly debated. Discussions focus on the rheological control of the deformation, the origin of the topography, and the role of surface processes and their relationship with deformation in the upper crust. To address these broad issues, we attempt to better understand when and how orogens form, evolve, and subsequently collapse. Several major issues that guide our research are as follows :
- How is deformation distributed in the evolution of an orogenic prism ?
- What is the role of foreland basins that are subject to sedimentation and thin-skinned tectonics during an orogen, and how do they evolve ?
- What are the factors (mechanical or surface) that determine the evolution of a mountain range to an orogenic plateau, and how does it evolve in response to gravitational forces and to the erosion of its borders ?

To answer these questions, our group will draw upon a wealth of disciplines and focus on two major collision zones (the collision of India-Asia and the Pyrenees), which will allow for the study of complex processes at various stages of the evolution of an orogen.

From the continental rift to the continent-ocean boundary (COB)

The accommodation of deformation during lithospheric extension is a much-debated scientific problem because it must encompass highly varied observed contexts and evolutionary scenarios : continental rifts, passive margins, or post-orogenic collapse. On a larger scale, the mechanisms and processes of extension are highly dependent on the rheological properties of the lithosphere, the rate of stretching, and its dynamics. In parallel, the topographic response, the interaction between tectonic structures, drainage systems, and ponds created during the extension are also controlled by those variables. Our approach to better constrain these complexes processes and variables will be based on a study of regions of the world where the geological and tectonic context is particularly noteworthy :

The Afar Province

Regarding the extreme lithospheric thinning and the transition between continental and oceanic domains, the East African triple junction and the margins of the volcanic Afar province are undoubtedly an ideal natural laboratory to detail and highlight (i) the different structures that achieve this final stage, and (ii) the role of the injection of magma in the accommodation of the extension and the establishment of segmentation. This region presents several well exposed sections of the whole margin (from the pre-rift traps to the active segments of the Afar depression) along which the implementation of our approach, combining quantitative geomorphology, structural geology, neotectonics and magmatism petrogenesis, is expected to produce original models. In particular, we intend to highlight the activity of structures that accommodate deformation during lithospheric thinning and that control the development of the first reliefs and basins. Additionally, we aim to understand the interactions between magma differentiation and dyke injection that control the installation and maintenance of the accretionary segments that are exposed at the centre of the Afar depression. Our quantitative approach to this problem that integrates volcanic petrology, tectonics, and geomorphology (which is unique to our group) will be present and funded at the national scale through the programme "Actions-Marges II".

The Corinthian Rift

The Corinthian rift is an outstanding example of a young, non-volcanic rift (<5 Ma) ; it is probably the most-active rift in the world and is associated with a significant seismic hazard. Due to the uplifting and rapid fluvial incision of the southern margin of the rift, the early stages of rifting have been exhumed and can be studied at the outcropping surface. Using a combination of structural geology, sedimentation, 3D modelling, biostratigraphic, magnetostratigraphic, and cosmogenic nuclide dating, we will study the evolution of the distribution of deformation at different time scales.

These studies will advance our understanding of the migration of the fault activity towards the north and NW in the context of variations in the expansion rate of the rift. The evolution of the geometry and kinematics of the network of normal faults in the upper crust, in connection with the mass redistributions induced by surface processes, is studied by combining onshore data with offshore data (seismic reflection) and deep seismic data (the ANR SISCOR project).