Geochronological and geochemical data from fracture-filling calcites from the Lower Pedraforca thrust sheet (SE Pyrenees)

U-Pb dating using laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), δ13C, δ18O, clumped isotopes and 87Sr/86Sr analysis, and electron microprobe have been applied to fracture-filling calcites and host carbonates from the Lower Pedraforca thrust sheet, in the SE Pyrenees. These data are used to determine the type and origin of migrating fluids, the evolution of the palaeohydrological system and timing of fracturing during the emplacement of this thrust sheet, as described in the article “From hydroplastic to brittle deformation: controls on fluid flow in fold and thrust belts. Insights from the Lower Pedraforca thrust sheet (SE Pyrenees)” – Marine and Petroleum Geology (2020). The integration of these data is also used to compare the fluid flow evolution of the Southern Pyrenees with that of other orogens worldwide and to generate a fluid flow model in fold and thrust belts. At a more local scale, the U-Pb dataset provides new absolute ages recording the deformation in the Lower Pedraforca thrust sheet, which was previously dated by means of indirect methods such as biostratigraphy of marine sediments and magnetostratigraphy of continental deposits

From early contraction to post-folding fluid evolution in the frontal part of the boixols thrust sheet (southern pyrenees) as revealed by the texture and geochemistry of calcite cements

Structural, petrological and geochemical (δ13C, δ18O, clumped isotopes, 87Sr/86Sr and ICP-MS) analyses of fracture-related calcite cements and host rocks are used to establish a fluid-flow evolution model for the frontal part of the Bóixols thrust sheet (Southern Pyrenees). Five fracture events associated with the growth of the thrust-related Bóixols anticline and Coll de Nargó syncline during the Alpine orogeny are distinguished. These fractures were cemented with four generations of calcite cements, revealing that such structures allowed the migration of different marine and meteoric fluids through time. During the early contraction stage, Lower Cretaceous seawater circulated and precipitated calcite cement Cc1, whereas during the main folding stage, the system opened to meteoric waters, which mixed with the connate seawater and precipitated calcite cement Cc2. Afterwards, during the post-folding stages, connate evaporated marine fluids circulated through newly formed NW-SE and NE-SW conjugate fractures and later through strike-slip faults and precipitated calcite cements Cc3 and Cc4. The overall paragenetic sequence reveals the progressive dewatering of Cretaceous marine host sediments during progressive burial, deformation and fold tightening and the input of meteoric waters only during the main folding stage. This study illustrates the changes of fracture systems and the associated fluid-flow regimes during the evolution of fault-associated folds during orogenic growth

Paleostress evolution in the South Pyrenean fold and thrust belt based on the structural analysis of fractures and U-Pb dating of carbonates

Structural analyses of vein and faults related with the growth of the South Pyrenean fold and thrust belt are coupled with the U-Pb ages of fracture-filling calcites compiled in Cruset et al. (2020) and Muñoz-López et al. (2022). Fractures include conjugated vein systems and reverse, strike-slip and normal faults cemented by calcite. The results reveal the orientation of tectonic stresses during the Pyrenean compression and their spatial and temporal evolution since the Late Cretaceous. Late Cretaceous to late Palaeocene U-Pb dates between 70.6 and 55.3 Ma registered compressional deformation in the inverted Mesozoic salt-related extensional basins corresponding to the Bóixols and Upper Pedraforca thrust sheets. Calculated paleostresses show a predominant N-S direction of tectonic transport, with more pronounced NW-SE directions in the western termination of the Bóixols and in the northern sector of the Upper Pedraforca. Fracture data and U-Pb ages between 47.9 and 42.3 Ma measured in the Lower Pedraforca thrust sheet reveal N-S and NW-SE directions of tectonic transport during the middle Eocene, similar to those in the Bóixols and Upper Pedraforca thrust units. Contrarily, younger late Eocene to Oligocene U-Pb ages between 36.2 and 28.4 Ma measured in the lowermost Cadí thrust sheet reveal an homogeneous N-S trend during the emplacement of this unit. Fractures cutting the Bóixols and Upper Pedraforca thrust sheets, and filled with cements yielding U-Pb ages from 48.8 to 25.68 Ma, show the same directions of tectonic transport than those measured for the Late Cretaceous-Paleocene. These Eocene and Oligocene ages also register the post-emplacement deformation of upper tectonic units on top of the Lower Pedraforca, Cadí, Montsec and Serres Marginals lower thrust sheets.This research was funded by the project ALORBE (PIE-CSIC-202030E310), DGICYT Spanish Projects PID2021-122467NB-C22 and PGC2018-093903-B-C22 Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación/Fondo Europeo de Desarrollo Regional, Unión Europea. David Cruset acknowledges the Spanish Ministry of Science and Innovation for the "Juan de la Cierva Formación¿ contract FJC2020-043488-I AEI/10.13039/501100011033

Crestal graben fluid evolution during growth of the Puig-reig anticline (South Pyrenean fold and thrust belt)

The Puig-reig anticline, located in the South Pyrenean fold and thrust belt, developed during the Alpine compression, which affected the upper Eocene-lower Oligocene sediments of the Solsona and Berga Formations. In this study, we highlight the controls on formation of joints and reverse, strike-slip and normal faults developed in the crest domain of the Puig-reig anticline as well as the relationships between fluids and these fractures. We integrated structural, petrographic and geochemical studies, using for the first time in the SE Pyrenees the clumped isotopes thermometry to obtain reliable temperatures of calcite precipitation.Structural and microstructural analysis demonstrate that at outcrop scale fracturing was controlled by rigidity contrasts between layers, diagenesis and structural position within the anticline, whereas grain size, cementation and porosity controlled deformation at the microscopic scale. Petrographic and geochemical studies of calcite precipitated in host rock porosity and fault planes reveal the presence of two migrating fluids, which represents two different stages of evolution of the Puig-reig anticline. During the layer-parallel shortening, hydrothermal fluids with temperatures between 92 and 130. °C circulated through the main thrusts to the permeable host rocks, reverse and most of strike-slip faults precipitating as cement Cc1. During the fold growth, meteoric waters circulated downwards through normal and some strike-slip faults and mixed at depth with the previous hydrothermal fluid, precipitating as cement Cc2 at temperatures between 77 and 93. °C.Integration of the results from the Puig-reig anticline in this work and the El Guix anticline indicates that hydrothermal fluids did not reach the El Guix anticline, in which only meteoric and evolved meteoric waters circulated along the fold. © 2016 Elsevier Ltd.This research was performed within the framework of DGICYT Spanish ProjectCGL2015-66335-C2-1-R, Grup Consolidat de Recerca “Geologia Sedimentària” (2014SGR-251).Peer reviewe

Fluid Flow during compressional and subsequent extensional regimes in the Estamariu thrust (Pyrenean Axial Zone).

X Congreso Geológico de España, 5-7 Julio 2021, Vitoria - GasteizCalcite veins precipitated in the Estamariu thrust during two tectonic events have been investigated in order to decipher the relationships between deformation and fluid migration in Paleozoic basement rocks. Structural observations constrain the timing of vein formation and fluid migration, whilst geochemical analyses (¿13C, ¿18O, 87Sr/86Sr and elemental composition) of the related calcite cements indicate the fluid origin, pathways and extent of fluid-rock interaction. The first tectonic event, related to the Alpine reactivation of the Estamariu Variscan thrust, is characterized by the upward migration of fluids derived from the crystalline basement, giving rise to the precipitation of calcite cements Cc1 and Cc2. The second tectonic event, developed during the Neogene extension, was responsible of the reactivation of the Estamariu thrust and the development of normal faults and shear fractures in which calcite cements Cc3, Cc4 and Cc5 precipitated. Cc3 and Cc4 precipitated from meteoric fluids that interacted at depth with basement rocks before upflowing through fault zones and related structures. Cc5 precipitated from meteoric fluids percolating from the surface through small fractures.This research was funded by the Spanish Projects CGL2015-66335-C2-1-R and PGC2018-093903-B-C22, and by the Grup Consolidat de Recerca “Geologia Sedimentària” (2017-SGR- 824). The PhD research of DM-L is supported by the FPI2016 (BES-2016-077214) Spanish program from MINECO

Influence of basement rocks on fluid evolution during multiphase deformation: The example of the Estamariu thrust in the Pyrenean Axial Zone

Calcite veins precipitated in the Estamariu thrust during two tectonic events are studied in order to (i) decipher the temporal and spatial relationships between deformation and fluid migration in a long-lived thrust and (ii) determine the influence of basement rocks on the fluid chemistry during deformation. Structural and petrological observations constrain the relative timing of fluid migration and vein formation, whilst geochemical analyses (13C, 18O, 87Sr=86Sr, clumped isotope thermometry, and elemental composition) applied to the related calcite cements and host rocks indicate the fluid origin, pathways, and extent of fluid rock interaction. The first tectonic event, recorded by calcite cements Cc1a and Cc2, is attributed to the Alpine reactivation of the Estamariu thrust. Analytical data indicate that these cements precipitated from heated meteoric fluids (temperatures in the range of 50 to 100 C) that had interacted with basement rocks (87Sr=86Sr 0.71) before upflowing through the thrust zone. The second tectonic event, attributed to the Neogene extension, is characterized by the reactivation of the Estamariu thrust and the formation of normal faults and shear fractures sealed by calcite cements Cc3, Cc4, and Cc5. Analytical data indicate that cements Cc3 and Cc4 precipitated from hydrothermal fluids (temperatures between 130 and 210 C and between 100 and 170 C, respectively) that had interacted with basement rocks (87Sr=86Sr 0.71) and been expelled through fault zones during deformation. In contrast, cement Cc5 probably precipitated from meteoric waters that likely percolated from the surface through small shear fractures. The comparison between our results and already published data in other structures from the southern Pyrenees suggests that regardless of the origin of the fluids and the tectonic context, basement rocks have a significant influence on the fluid chemistry, particularly on the 87Sr=86Sr ratio. Accordingly, the cements precipitated from fluids that have interacted with basement rocks have significantly higher 87Sr=86Sr ratios (0.710) with respect to those precipitated from fluids that have interacted with the sedimentary cover (0.710), which involves younger and less radiogenic rocks. © 2020 Copernicus GmbH. All rights reserved.This research was carried out within the framework of the DGICYT Spanish project PGC2018-093903-B-C22 (Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación/Fondo Europeo de Desarrollo Regional, Unión Europea) and the Grup Consolidat de Recerca “Geologia Sedimentària” (2017-SGR-824). The PhD research of DML is supported by the FPI2016 (BES-2016-077214) Spanish program from MINECO.Peer reviewe

Changes in fluid regime in syn-orogenic sediments during the growth of the south Pyrenean fold and thrust belt

The eastern sector of the south Pyrenean fold and thrust belt developed during the Alpine compression and affected Upper Cretaceous to lower Oligocene foreland basin deposits. In this study, we determine the changes in fluid regime and fluid composition during the growth of this fold and thrust belt, integrating petrographic and geochemical data obtained from fracture-filling cements.Hydrothermal fluids at temperatures up to 154. °C, migrated from the Axial zone to the foreland basin and mixed with connate fluids in equilibrium with Eocene sea-water during lower and middle Eocene (underfilled foreland basin). As the thrust front progressively emerged, low-temperature meteoric waters migrated downwards the foreland basin and mixed at depth with the hydrothermal fluids from middle Eocene to lower Oligocene (overfilled non-marine foreland basin).The comparison of the fluid flow models from the Southern Pyrenees with other orogens worldwide, seems to indicate that the presence or absence of thick evaporitic units highly control fluid composition during the development of fold and thrust belts. Whereas in thrusts not detached along thick evaporite units, mixed fluids are progressively more depleted in δ18O and have a lower temperature and lower Fe and Sr contents as the thrust front emerges, in thrust detachments through thick evaporite units, the mixed fluids are enriched in δ18O. © 2017 Elsevier B.V.This research was performed within the framework of DGICYT Spanish Project CGL2015-66335-C2-1-R and ALPIMED Project (PIE-CSIC-201530E082), Grup Consolidat de Recerca “Geologia Sedimentària” (2014SGR-251).Peer reviewe

Changes in the fluid regime during successive reactivations of a Pyrenean thrust fault.

3rd Conference of the Arabian Journal of Geosciences (CAJG), Sousse, Tunisia, November 2-5 2020.The Estamariu thrust, in the Pyrenean Axial Zone, resulted from a long-lived Variscan to Neogene tectonic history. Structural data together with petrological and geochemical analyses of synkinematic calcite veins and host rocks, constrain the fault-fluid system evolution during two successive tectonic events. Despite the Estamariu thrust is known to be Variscan in origin, in the study area, it places a Devonian pr-eVariscan unit on top of a Stephano-Permian late- to post-Variscan sequence, indicating that the structures present within this fault zone have to be post-Variscan. Analytical data suggests that during the Alpine compression, the thrust was reactivated allowing the transposition of the Variscan regional foliation (Sr) within the main thrust zone and generating a subsidiary thrust zone in the footwall of the main thrust. During this episode, meteoric fluids (¿18O fluid = -6.4 to -0.3 ¿VSMOW), heated at depth (temperatures between 56 and 98 ºC) and interacted with basement rocks (87Sr/86Sr ratio > 0.71) before ascending through the fault zone. These ascending fluids progressively increased the fluidrock interaction from the thrust plane towards the hanging wall. During the Neogene extension, the Estamariu thrust was reactivated and normal faults and shear fractures developed. During this period, hydrothermal fluids (temperatures up to 208 ºC), derived from the basement (¿18 Ofluid up to +12 ¿VSMOW and 87Sr/86Sr ratio > 0.71), migrated upwards through reactivated and newly formed fault zones. Finally, during the latest to post stages of extension and uplift of the structure, the fluid regime changed to percolation of low temperature meteoric fluids migrating from the surface through small shear fractures. Neogene extensional faults are still conduits of current hydrothermal springs in the study area. Thus, these structures have probably been acting as conduits for hydrothermal fluids from Neogene times to present in the Pyrenean Axial Zone