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In orogens, shortening is mainly accommodated by thrusts, which constitute preferential zones for fluid-rock interactions. Fluid flow, mass transfer, and mineralogical reactions taking place along thrusts have been intensely investigated, especially in sedimentary basins for petroleum and uranium research. This study combines petrological investigations, mineralogical quantifications, and geochemical characterizations with a wide range of analytical tools with the aim of defining the fluid properties (nature, origin, temperature, and redox) and fluid-host rock interactions (mass transfers, recrystallization mechanisms, and newly formed synkinematic mineralization) in the Pic-de-Port-Vieux thrust fault zone (Pyrenees, Spain). We demonstrate that two geochemically contrasted rocks have been transformed by fluid flow under low-grade metamorphism conditions during thrusting. The hanging-wall Triassic red pelite was locally bleached, while the footwall Cretaceous dolomitic limestone was mylonitized. The results suggest that thrusting was accompanied by a dynamic calcite recrystallization in the dolomitic limestone as well as by leaching of iron via destabilization of iron oxides and phyllosilicate crystallization in the pelite. Geochemical and physical changes highlighted in this study have strong implications on the understanding of the thrust behavior (tectonic and hydraulic), and improve our knowledge of fluid-rock interactions in open fluid systems in the crust., Author(s): Vincent Trincal [sup.1] [sup.2] , Martine Buatier [sup.1] , Delphine Charpentier [sup.1] , Brice Lacroix [sup.3] , Pierre Lanari [sup.4] , Pierre Labaume [sup.5] , Abdeltif Lahfid [sup.6] , [...]

The mechanisms of Mg-phyllosilicate formation in a hydrothermal system at a sedimented ridge, Middle Valley, Juan de Fuca, provide vital information on fluid pathways and the movement of chemical elements. The precipitation of minerals depends on the permeability, fluid chemistry and temperature. Details of the geochemical and mineralogical study of the hydrothermal system are given.