Syn‐orogenic fluid flow in the Jaca basin (south Pyrenean fold and thrust belt) from fracture and vein analyses

Abstract

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,

First investigation of quartz and calcite shape fabrics in strained shales by means of X-ray tomography

“…The Jaca basin is a piggyback basin of the South Pyrenean foreland, incorporated in the Pyrenean Orogeny from the Eocene to the Early Miocene (Labaume et al, 1985;Hogan & Burbank, 1996;Izquierdo-Llavall et al, 2013;Crognier et al, 2018). The Northern part of the Jaca Basin is made up of the Hecho turbiditic group.…”

“…Cleavage develops as axial planes parallel to the major folds axes (mostly oriented N100o) but damage is induced by thrust propagation. At ~2 km south from the emerged thrust, there is no cleavage, and shales are only affected by a fracture network (Crognier et al, 2018). We refer to this type of petrofabric, corresponding to a low strain area, as "cleavage-free" throughout the text.…”

From Early Contraction to Post-Folding Fluid Evolution in the Frontal Part of the Bóixols Thrust Sheet (Southern Pyrenees) as Revealed by the Texture and Geochemistry of Calcite Cements

“…Studies integrating the evolution of fracture systems and related cements are needed to constrain the fluid-flow history of an area during orogenic growth and, therefore, understand the nature and origin of fluids that circulate through time, the diagenetic process evolution, changes in reservoir properties such as porosity and permeability and the distribution of minerals and hydrocarbons [28,29].During recent years, the interest in this topic has significantly increased [30][31][32][33], giving rise to many new studies that have tackled this topic in compressional, extensional and strike-slip tectonic settings worldwide. Some recent examples are from the Ionian fold and thrust belt in Albania [22,34,35], the Apennines [36-40], the Alps [41,42], the Zagros Mountains [43], the Sicilian belt [44], the Oman Mountains [45-48], the Catalan Coastal Range [49-53] and the Pyrenees [16,17,19,24,[54][55][56][57]. The South Pyrenean fold and thrust belt is well known as an outstanding field analogue for the study of fluid migration during orogenic compression due to the excellent preservation of its sedimentary record, the high-quality exposure of structures and the complex relationships between folding and thrusting and syntectonic sediments [19,58].…”

Brittle tectonics and fluids overpressure during the early stage of the Bay of Biscay opening in the Jard-sur-Mer area, (northern Aquitaine Basin, France)

“…Recently, several episodes of fluid overpressure-related fracturing have been documented at the southern boundary of the Aquitaine Basin: during the Lower Cretaceous first (Salardon et al, 2017;Renard et al, 2019) and then during the Eocene (Crognier et al, 2018). We focus here on an area that offers good outcropping conditions in the north of the Basin and shows a thick mineralization-bearing cover (Fig.…”