Understanding how deformation, fluids, and mineral changes interact is central to crustal evolution models. The North Pyrenean Zone, located in the Pyrenean retrowedge, corresponds to an inverted early-Cretaceous rift leading to mantle exhumation. It comprises Mesozoic basins and Variscan basement massifs. Key rifting markers include: (i) thick Albian-Cenomanian detrital sequences, (ii) peridotite bodies reworked into syn-rift sediments, (iii) HT-LP metamorphism of pre-/syn-rift series, and (iv) large-scale metasomatism, evidenced by several talc schists and albitite occurrences. The 3D-4D fluid reservoir model linked to this metasomatism remains poorly constrained.
Our study focuses on the eastern part of the Arize Massif, which exposes a Variscan section from migmatites in the south to low-grade Carboniferous schists in the north. Its northern and eastern borders correspond to a curved fault transitioning from N100°E-oriented normal fault in the north to N–S-oriented left-lateral fault in the east. This fault separates two structural domains: to the east, the Saint-Barthelemy Massif shows a gently dipping, N100°E-oriented foliation, while to the west, the eastern Arize shows a N140°E-oriented left-lateral fault network and a kilometer-scale fold with a steeply-plunging fold axis (304°/62°). This fold, affecting the foliation, hosts all metasomatized rocks.
At structurally shallower levels (Carboniferous), the fault network is filled by Fe-mineralization or massive quartz. At deeper levels, pervasive albitization is associated with a three-stages alteration: (i) biotite chloritization and quartz disappearance; (ii) albite replace feldspars; (iii) calcic paragenesis crystallization and neoformed albite. Locally, a late quartz, chlorite ± carbonates assemblage precipitated in the secondary porosity. Initial results show that fluid inclusions trapped in metasomatized apatite and late quartz contain H2O-NaCl-CaCl2 brines (≈ 15% salinity). To further characterize albitization processes, microthermometric, microstructural, geothermometric, and geochronological analyses are ongoing.
These data reveal the functioning of a N140°E linkage-zone connecting two N100°E rift segments. High fault connectivity favored deep fluid percolation. We propose seawater-derived fluids interacted with Triassic evaporites before migrating into the basement. Upward flow, progressively enriched in Fe through albitization at intermediate levels, controls Fe mineralization higher up. This integrated study highlights the role of linkage-zones in fluid flow in thinned continental crust, with implications for hydrothermal and geothermal systems.