Fluid flow patterns during Pyrenean thrusting

Abstract

Geochemical data for fluid circulation patterns during thrusting in the Pyrenees are reviewed. New halogen data from fluid inclusions suggests that brines responsible for metasomatic alteration in shear zones, and expelled along the Gavarnie Thrust, were of evaporitic origin. These brines mixed with more dilute formation waters in a topographically driven flow system at higher levels. The brines probably formed in the Triassic and were also involved in the formation of Mesozoic Pb–Zn deposits. Dense fluids are hard to completely expel from upper crustal rocks, and recycling of such fluids through several metasomatic events is probably a common process.