Géodynamique

Strain localisation in the continental lithosphere

The interplay in time and space between shear zones and faults is a key control on lithosphere deformation and plate tectonics, but its understanding is still elusive. To better constrain how strain progressively localises and how ductile and brittle deformations interact, we apply an approach combining field work, experimental deformation, Ar-Ar radiometric dating and numerical modelling. The targets of the field work are exhumed crustal shear zones within the Mediterranean domain or the Norwegian Caledonides and deep domains of fossil accretionary prisms in Japan. Dense sampling of Ar-Ar radiometric ages across km-scale shear zones coupled with fine-scale P-T and petrofabric analysis is applied to constrain localisation as a function of exhumation across the ductile-to-brittle transition. State-of-the-art facilities including in situ (UV laser) and step-heating (CO2 lasers) microprobes are employed to investigate grain-scale Ar-Ar age variations as a function of deformation. Finally, the parameters governing strain localisation are explored through numerical modelling. This research topic is financially supported by the ERC Senior Grant “Rheolith” of Laurent Jolivet and Evguenii Burov.

Interactions between chemical reactions and rheology

In a wide range of geological settings, including subduction, collision and extension, deforming rocks are also experiencing simultaneously chemical reactions. These reactions bear a great influence on rheology, through the variations in the mineral assemblages, the metastability of some mineral phases, the production/consumption of fluid or the change in grain size. To address this general question, we designed experiments in the Paterson and the Griggs apparatus and focus on four different problems: the frictional stability of subducting sediments, the relation between melting and deformation in granitic magmas, the role of water for quartz weakening and the formation of mantle shear zones.

Intracontinental orogens

Our research project aims at constraining the role of inherited crust structure on the development of intracontinental collisional ranges. In the Pyrenees (southern France) the compressional structures developed during the Iberian-Eurasian collision are strongly controlled by structures resulting from the Variscan orogeny, Trias to lower Lias extension and magmatism and, then, from a rifting episode localized in this area and developed during Cretaceous. Our work particularly focuses on the structures developed within the Mesozoic series (in particular the marble units) during compression, in order to better understand their role in the localisation of the deformation during compression.

Mesozoic magmatism of South China

The Mesozoic magmatic province of South China is one of most important in the world. In addition to the various petrological rock types, it includes numerous ore deposits (Au, W, Sn, Sb, Pb, Zn, U) associated to plutonism. In order to understand its petrogenesis, the tectonics-magmatism relationships and the geodynamic context, most of investigations conducted up to now were focused on geochemistry and geochronology. A few number of studies have been carried out in structural geology, thermo-barometry, experimental petrology, rock magmatism, and gravity modelling. Our multidisciplinary study, led in collaboration with Nanjing University aims at deciphering the understanding of this exceptional magmatism.

Paleozoic accretionary orogens of Central Asia

The Central Asia Orogenic Belt (CAOB), with more than 5 000 km long, is one of the largest Paleozoic accretionary belts in the world, associated with many world-class ore deposits. However, the relative role of orogenic mechanisms: oceanic subduction, continental/microcontinental subduction, and strike-slip motion, and the timing (Early or Late Paleozoic–Early Mesozoic) of this accretion are still hotly debated. Moreover, the evolution after accretion is also poorly constrained. Our collaborations in structural geology, paleomagnetism, sedimentology and geochronology with Nanjing University and Peking University will improve the fundamental understanding of the accretion and its evolution, and contribute to debate as well.