Fluid evolution from extension to compression in the Pyrenean Fold Belt and Basque-Cantabrian Basin: A review

Abstract

We propose a review to discuss the large number of studies dealing with the fluid history in extensional and compressional sedimentary basins that evolved along the Iberian-Eurasian plate boundary during the full Mesozoic-Cenozoic Wilson Cycle in the Pyrenean fold belt and the Basque-Cantabrian Basin. We integrate classic and modern geochemical and geochronological datasets used in fluid studies with the current tectonic knowledge of the studied area.Late Hercynian fluid systems were dominated by Carboniferous-early Permian magmatic intrusions related to large-scale lithospheric delamination at the end of the collision, which caused the accumulation of skarns at depths of 8000–10,000 m during contact metamorphism. During the Mesozoic extension, early and widespread shallow burial dolomitization of Jurassic and Early-Cretaceous carbonates occurred at burial depths of 500–1000 m due to seawater influx. From Albian to Cenomanian, along the North Pyrenean extensional fault zone, contact metamorphism processes occurred in association with mantle-derived and deep-crustal fluids at temperatures higher than 300 °C, which interacted with Triassic evaporites and formation and marine waters and depths of 2000–3000 m. Away from this fault, fluid systems were dominated by hydrothermal dolomitization and the accumulation of ZnPb mineralization along diapir walls and faults, whereas in the less extended and proximal domains of the extensional system, fluids were formation waters at temperatures up to 150 °C. The Alpine compressional fluid history registers the increasing influence of meteoric fluids as the foreland basin became overfilled and fluid flow occurred at depths of 2.5–4 km in tectonic units detached in Triassic evaporites and of >4 km in units rooted at depth with the Paleozoic basement. Along and across strike differences in the fluid evolution of the Pyrenees are attributed to changes in the structure of the cover and basement tectonic units, the westward decrease of shortening and in the oblique directions of Upper Triassic successions, which acted as very efficient seals for deep-sourced fluids.Subvertical walls of diapirs are baffles for fluid flow, whereas fracturing and deposition of porous halokinetic successions are effective conduits. Evaporite detachments compartmentalize paleohydrological systems during tectonic deformation, although they may be breached by fluids reaching lithostatic pressures. In large evaporite-bearing provinces, fluid systems may share common patterns during successive extensional and compressional tectonic events, as documented in the Western Mediterranean Mesozoic extensional rift system. In this area, metal-bearing and deep-sourced fluids interacted with Triassic sulphates and organic matter, triggering the accumulation sulphides in rock porosity. However, more research is needed in other large-scale evaporitic provinces of different ages to identify common fluid flow patterns.