A Thermal Model of the Flamanville Granitic Diapir Deforming Aureole

Diapiric intrusions induce significant thermal and mechanical changes in the surrounding host rock, including heating and deformation. While previous studies have focused on intrusion formation, few models detail the thermal field evolution during progressive pluton boundary migration, even less, with the associated host-rock deformation. This study aims to simulate the Flamanville granitic diapir's growth and cooling processes to investigate the coupling between thermal evolution and deformation in the aureole during contact metamorphism. The Flamanville intrusion, located in Normandy, northwest France, is a homogeneous, coarse-grained granodioritic diapir with an elliptical geometry, measuring 7.4 km (E-W) by 4.5 km (N-S), and a maximum depth of over 3 km. The pluton intruded Cambrian to Devonian meta-sediments around 318 ± 1.5 Ma. The contact metamorphic aureole extends up to 1 km from the pluton boundary, where intense deformation is characterized by radial shortening, concentric stretching, boudinage, and shear structures. A thermal model is constructed using OpenFOAM 11, an open-source computational fluid dynamics (CFD) platform. To accurately capture the dynamic emplacement of the Flamanville pluton, a custom solver is developed to incorporate an adequate advection term into the thermal diffusion equation, representing the gradual migration of the Flamanville pluton boundary during its emplacement. The solver accounts for the spatial variation in deformation intensity within the aureole, where deformation decreases systematically with increasing distance from the diapir, reflecting observed field patterns of shortening, stretching, and shear structures. Approximately 90 host-rock samples were collected across the aureole to determine maximum metamorphic temperatures using the Laser Raman Spectroscopy Carbon Geothermometer (RSCM) method. The temperatures, ranging from 250°C to 650°C, provide a robust dataset for validating the thermal model and defining the thermal variation in the aureole. This numerical model will simulate the thermal evolution of the host rock during diapiric growth and cooling. By comparing the results with Raman-derived temperature profiles, it is expected to facilitate a quantitative analysis of the evolution of the thermal field within the aureole, offering advanced insights into the thermal regimes governing aureole deformation and contact metamorphism processes.

 

Key words: Numerical modeling; thermal evolution; aureole deformation; Flamanville granitic diapir; contact metamorphism; Raman Spectroscopy Carbon Geothermometer (RSCM)