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An analysis was performed of the fracture networks in the N-S trending thick-skinned Malargüe fold and thrust belt (MFTB). A total of 2000 planar structures including joints and veins were measured in different structural domains ranging from surficial thin-skinned systems detached in the cover to large-scale structures such as basement-cored folds. The investigated stratigraphic section ranges from the Middle Jurassic (Cuyo Group) to the Paleocene (Malargüe Group), including sandstones, siltstones, shales, and limestones. Four main fracture sets are identified trending, E-W, NW-SE, NE-SW, and N-S. The abutting relationships provide a reliable chronology between the four fracture sets which are ubiquitously found in the MFTB throughout the various structural domains. Due to this observation, we assume the fracture signal to be regional and developed in response to both large-scale processes and folding. In particular, based on a fold test and the characteristics of data dispersion, the fracture sets I, II, and III exhibit a prefolding origin, while set IV shows a synfolding origin. A regional interpretation of the various fractures is proposed, involving several stages of fracture formation from compaction to folding, including prefolding layer parallel shortening. The fracture signal yields useful insights about the structural history of the MFTB and the spatiotemporal evolution of the foreland tectonic regime since Late Cretaceous times. We then place the various identified fracture sets into the known pattern of geodynamic evolution since the Late Cretaceous.

This study aims at understanding the origin and nature of syn-orogenic fluid flow in the Jaca basin from the South Pyrenean fold and thrust-belt, as recorded in calcite and quartz veins of the Sierras Interiores (Spain) and the turbiditic basin, which cover upper Cretaceous to Late Eocene syntectonic deposits. The fracture network consists of a classical pattern of transverse and longitudinal fractures related to Layer Parallel Shortening (LPS) and folding respectively. Veins filled equally about the third of fractures in the carbonate shelf and turbidites. Carbon and oxygen isotopes of calcite veins mostly indicate precipitation from isotopically buffered water, consistent with high water-rock interaction. In the Sierras Interiores, petrographical observations and fluid inclusion microthermometry are consistent with two distinct stages of precipitation. The first stage is characterized by relatively low Th and low salinities (155-205°C and 0.5-3.2 wt% eq. NaCl). The second stage, which was characterized both by the formation of mode-I joints and by mode-I reactivation of pre-existing veins, shows higher Th and salinities (215-270°C and 2.2-5.7 wt% eq. NaCl). Waters recorded in the second stage are interpreted to have interacted with underlying Triassic evaporites and flowed along major thrusts before vein precipitation, which are locally in thermal disequilibrium with hostrocks. We suggest the transition from a rather closed hydrological system during the first stage of vein formation, interpreted to have occurred during Eaux-chaudes thrusting (upper Lutetian-Bartonian), to a more open hydrological system during the second stage, which likely occurred during Gavarnie thrusting (Priabonian-early Rupelian). Finally, we also document the migration in space and time of hydrothermal pulses along the South Pyrenean Foreland Basin, related to the westward propagation of major thrusts during the Pyrenean orogeny.Correspondence: N. Crognier,