Résumé
Retrieving records of metamorphism and associated processes at peak pressure (peak-P) is challenging because most lithologies re-equilibrate at the thermal peak of metamorphism (peak-T). Accessing the record of peak-P (maximum depth) is critical to resolve the tectonic process in which metamorphism took place. Gneiss domes exhume material from lower- to shallow-crustal levels via vertical and lateral flow. Although dominated by felsic rocks that readily re-equilibrate at LP-HT in the shallow crust, gneiss domes often contain mafic rocks that have potential to preserve a more complete record of their metamorphism. In the Montagne Noire dome (French Massif Central), small volumes of eclogite outcrop in the core and margins of the dome. These eclogites provide a snapshot of the HP-conditions from which they were exhumed. Our work integrates multiple methods and tools from the metamorphic kitchen sink to investigate the records of metamorphism at maximum depth and in the early stages of exhumation preserved in these eclogites. We combine in situ O-isotope analyses (garnet, zircon) and U-Pb petrochronology of eclogite-facies minerals (zircon, rutile) with high-resolution quantitative EPMA mapping of textures developed at peak-P (eclogite-facies phases) and at the onset of exhumation (symplectites) to calculate P-T conditions associated with deep crustal flow at various stages of doming. Results show that eclogites record physicochemical interactions between felsic and mafic lithologies while residing in the deep crust and during the early stages of exhumation. We demonstrate that eclogites from distinct localities record different extents of interactions with the surrounding partially molten gneisses, and experienced distinct P-T paths ascribed to differing exhumation trajectories. Together, these results provide a glimpse of the processes, metamorphic conditions, and trajectory of deep crustal flow during orogenesis, consistent with numerical modeling of gneiss dome formation, and provide a unique view of how the deep crust is internally mobilized in orogens. Resolving the magnitude and conditions of exhumation of large, hot volumes of crust informs the processes involved in the internal recycling, thermal equilibration, and rheological evolution of reworked continental crust.