The South Pyrenean triangle zone represents the southernmost front of the Pyrenees at its central portion deforming the Upper Eocene‐Miocene Ebro Basin deposits. Two main structures characterize its western termination, the Barbastro anticline and the San Román backthrust, which detached on the Barbastro Formation (and lateral equivalents), an Upper Eocene‐Lower Oligocene syntectonic evaporite‐rich formation that acted as a multidetachment unit. Northward, the south directed Pyrenean thrust unit (i.e., Gavarnie‐Sierras thrust sheet) detached along the Middle‐Upper Triassic evaporitic rocks to finally ramp up and glide along the same Upper Eocene‐Lower Oligocene multidetachment unit. A multidisciplinary approach allowed constructing a detailed structural and stratigraphic model of the study area. The workflow consisted of (1) constraining the geometry and structural architecture based on surface geology, interpretation of seismic lines (>900 km), and wells and (2) obtaining the 3‐D density distribution of the multidetachment unit using gravity stochastic inversion (more than 7,000 gravity stations and 1,500 density data). The geometry of the sole thrust of the Gavarnie‐Sierras thrust sheet was controlled by the distribution of the evaporite‐rich units of the Barbastro Fm. Weak detachments promoted thrust salient formation and thrust flat geometries. The western termination of the South Pyrenean triangle zone is defined as a westward transition from a ramp‐dominated and multiple triangle zone to a detachment‐dominated one. Its geometry, kinematics, and location were controlled by the heterogeneous lithology of the Barbastro Fm. and its basal, halite‐based detachment southern pinch‐out., This work was financed by the DR3AM (CGL2014‐54118‐C2‐2‐R) and E‐28(GeoApp Research Group) projects by the Spanish Ministry of Science and the Aragón Government, respectively. This work has received support from and it also aligns with methodological goals of the GeoERA project 3DGeoEU (ERANET Cofund action 731166 [H2020], Project code GeoE.171.005) and GeoPiri3D project (from the Spanish Ministry of Education and Universities, project code CGL2017‐84901‐C2‐2‐P). We acknowledge the TopoIberia project for providing the gravity data from SITOPO databases.The Academic agreement with MVE is also acknowledged. The IHS is also acknowledged for providing the Kingdom Suite software. José María
Llorente and Agustín Gonzalez are here acknowledged for gravity data acquisition
and processing. We also want to thank reviewers Christoph v. Hagke and Jonas Kley and Editor Laurent Jovilet for their productive suggestions and comments that helped to enrich our work and improve the manuscript., Peer reviewed

A new gravity survey (1164 gravity stations and 180 samples for density analysis) combined with two new geological cross sections has been carried out in a sector of the Central Pyrenees in order to improve the characterization of basement and cover architecture. From North to South, the study area comprises the southern half of the Axial Zone and the northernmost part of the South-Pyrenean Zone. New gravity data were combined with previous existing databases to obtain the Bouguer and residual anomaly maps of the study area. The two cross sections, oriented NNE–SSW, were built from field data and previous surficial and subsurface data and cross the La Maladeta plutonic complex. The residual anomaly map shows values ranging from −18 to 16 mGal and anomalies mainly oriented N120E. The two 2.5D modelled cross sections show similar observed gravity curves coinciding with similar interpreted structural architecture. Data show a gravity high oriented N120E coinciding with the Orri basement thrust sheet and an important gravity depression, with the same orientation, coinciding with the leading edge at depth of the Rialp basement thrust sheet and interpreted as linked to a large subsurface accumulation of Triassic evaporites. The volume at depth of the La Maladeta and Arties granites has been constrained through gravity modelling. This work highlights that the combination of structural geology and gravity modelling can help to determine the structural architecture of an orogen and localize accumulations of evaporites at depth., This work is part of the project CGL2017-84901-C2-2-P funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe” and project PID2020-114273GB-C22 funded by MCIN/AEI/10.13039/501100011033 from Spanish Ministry of Science, Innovation and Universities. Seequent has provided us the GM-SYS module of the Oasis Montaj. The authors acknowledge the contribution of José María Llorente and Agustin González for the acquisition of the gravity data. We thank to Aigüestortes National park and Alt Pirineu Natural park their logistic support. We thank anonymous reviewer for improving the content in the manuscript. This study represents a contribution to GeoAp Research Group (E01-20R) (Aragón Government)., Peer reviewed

The data is available under request and free of charge. Gravity data from the GeoPiri3D project (2.5D and 3D characterization of the crustal structure of the Catalan Pyrenees with special attention to granitic bodies and Permocarboniferous volcano-sedimentary basins http://hdl.handle.net/10261/254934, In this work, we present new Bouguer and residual Bouguer anomaly maps of the Central Pyrenees calculated from 3590 stations, of which 1141 are new observations acquired from surveys performed between 2018 and 2019. The most prominent feature of the Bouguer anomaly is the long wavelength elongated minimum in its central part that continues to the W and ends towards the E with a positive gradient that seems to envelope the minimum. Other short and medium wavelength minima are superimposed, some placed over the batholithic outcrops. In the residual Bouguer, the main relative minima are related with outcrops of batholiths or interpreted buried granites except for the prominent minimum South of La Maladeta Granite, associated with Triassic evaporitic accumulations. These maps (shown on the Main Map) will help characterizing the Permo-Carboniferous batholiths of the Central Pyrenees, in particular La Maladeta and Andorra Mont-Louis granites in order to add constraints to the mechanism of their emplacement., The authors thank the financial support from the CGL2017-84901-C2-2-P funded by MCIN/AEI/10.13039/501100011033 and ‘ERDF A way of making Europe’ and project PID2020-114273GB-C22 funded by MCIN/AEI/10.13039/501100011033. T, Peer reviewed

The aim of this work is the application of the anisotropy of magnetic susceptibility (AMS) to the study of volcanic materials from the Late Carboniferous-Permian Cadí basin (southern Pyrenees) in order to (i) explore the limits of this technique in ancient volcanic materials that have undergone strong chemical alteration and a complex tectonic evolution and (ii) provide new insights on the deposition of volcanic materials in this tectonically controlled sedimentary basin. To establish a comparison with the petrofabric of rocks, AMS was complemented with observations and orientation analyses at the outcrop scale, in oriented polished blocks and in thin sections under the microscope. High resolution sampling (620 specimens from 56 sites located in five transects along a sequence 150 m thick) allowed to characterize the volcaniclastic and lava flow series. The AMS results show a fairly constant average magnetic lineation oriented WNW-ESE (in situ and tilt-corrected) and two secondary maxima (N-S to NE-SW in some areas). The magnetic mineralogy analyses indicate the contribution of paramagnetic and ferromagnetic (magnetite, Tc 580 °C) phases to susceptibility. The magnetic fabric has a close relationship with the spatial distribution and orientation of the mineral and grain components of the studied rocks, mainly controlled by depositional processes, with a negligible contribution of the tectonic imprint. Therefore, the magnetic lineation (i.e. K1 axes) can be reliably used as a paleoflow indicator. Nevertheless, it was not possible to establish a clear correspondence between lithological and magnetic fabric types. The results obtained indicate that the AMS approach represents a powerful tool to infer the paleoflow pattern in ancient volcanic and volcaniclastic rocks, even under a priori unfavourable conditions., This work was supported by projects grants CGL2017-84901-C2-2-P, PID2020-114273GB-C22, PID2019-108753GB-C22 and FPU19/02353 funded by MCIN/AEI/10.13039/501100011033, “ERDF A way of making Europe” and “ESF Investing in your future”., Peer reviewed

In this work we establish reliable correlations between density and magnetic susceptibility in three paramagnetic granites from the Pyrenees. In total, 128 sites (310 density measurements and >2600 susceptibility ones) were studied in the Mont Louis-Andorra, Maladeta and Marimanha granitic plutons covering the main range of variability of magnetic susceptibility. Regressions were calculated for every granitic body and an integrated linear function was obtained for the entire dataset: ρ (kg/m3) = 2566 (kg/m3) + 0.541κ (10−6 S.I.) (R:0.97). This relationship is only valid in the paramagnetic domain, where iron is mostly fractioned in iron-bearing phyllosilicates and the occurrence of magnetite is negligible (or at least its contribution to the bulk susceptibility). This relationship, likely different in other bodies, allows for transforming magnetic susceptibility data into density data, helping to constrain gravity modelling when density data from rock samples are scarce. Given the large amount of AMS studies worldwide, together with the quickness and cost-effectiveness of susceptibility measurements with portable devices, this methodology allows for densifying and homogenizing the petrophysical data when modelling granite rock volumes based on both magnetic and gravimetric signals., This work was financed by the projects GeoPiri3D (CGL2017-84901-C2-2-P), UKRIA4D (PID2019-104693GB-I00/CTA) and IMAGYN (PID2020-114273GB-C22) from the Spanish Ministry of Science (funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”). This work is methodologically related also with the 3DGeoEU project financed by the European Commission under the ERANET Cofound action GeoERA (Grant No.: 731166). The GeoAp Research group from the Aragonian Government is also acknowledged. We are also in debt to the staff of the Petrophysical Laboratory (IGME, Tres Cantos) and to the Geophysics technicians (José Mª Llorente and Agustín González). The help of the Rock Magnetism Laboratory of the Centre Européen de Recherche et d’Enseignement de Géosciences de l’Environnement (CEREGE) in Aix en ProvenceMarseille is also acknowledged. P.C. acknowledges funding from PTA2017-14779-I and FJC2019- 041058-I (AEI-Spain) contracts. E.B. thanks the Geomodels Research Institute of the University of Barcelona and GGAC-2017SGR596 (Generalitat de Catalunya)., Peer reviewed

The Pyrenees constitutes an exceptional example of an Alpine orogenic belt characterized by basement thrust sheets involving Paleozoic rocks and Mesozoic and Cenozoic cover units detached on the Triassic evaporites, the main décollement level. This work is located in the Central Pyrenees, where gravity data help to better constrain the internal architecture of the upper crust of the southern half of the Axial Zone and the northern part of the South Pyrenean Zone, a key area to understand the orogenic evolution of the chain. Previous and new gravity, petrophysical and geological data have been used to obtain the Bouguer and residual anomaly maps of the study area and six serial gravity-constrained cross sections perpendicular to the main structural trend. The residual anomaly map shows a good correlation between basement units involved in thrust sheets of the study area and gravity highs whereas negative anomalies are interpreted to correspond with Mesozoic/Cenozoic basins, Triassic evaporites, Late Variscan igneous bodies, and Ordovician gneisses. The six gravity-constrained cross sections highlight strong along-strike variations on the gravity signal due to lateral differences of the superficial and subsurface occurrence of Triassic evaporites, different geometry at depth of the Late Variscan igneous bodies outcropping in the study area, and geometric lateral variations of the basement thrust sheets and their relationship with the Mesozoic-Cenozoic units., This work was funded by projects CGL2017-84901-C2-2-P funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”, PID2020-114273GB-C22 funded by MCIN/AEI/10.13039/501100011033 from the Spanish Ministry of Science and Innovation, and "Severo Ochoa” extraordinary grants for excellence IGME-CSIC (AECEX2021)., Peer reviewed

El proyecto GeoPiri3D tiene como objetivo caracterizar la geo-metría y la cinemática de los batolitos permo-carboníferos del Piri-neo Central por medio de una combinación de campos potenciales y de datos estructurales. Durante 2018 se han adquirido 824 nuevas estaciones de gravedad y 186 muestras de roca. Los datos de gra-vedad se han procesado e integrado en la base de datos del IGME y se ha calculado un nuevo mapa de anomalías de Bouguer. Los dos cuerpos graníticos principales (La Maladeta y Andorra-Mount Louis) proporcionan diferentes respuestas gravimétricas. La anomalía sobre el afloramiento de granito de La Maladeta presenta pequeñas variaciones en su amplitud que se asocian con cambios de facies. Los datos petrofísicos proporcionan una densidad media de ca. 2, 6 g/cm3 que son consistentes con su composición, predominantemente granodiorítica. El afloramiento del plutón de Mount Louis-Andorra se caracteriza por un mínimo relativo, lo que sugiere una composición predominantemente granítica (aún no se tienen resultados de las me-didas de densidad). Además, el mínimo se extiende en dirección NE, lo que sugiere que parte del plutón está enterrado. El mínimo relativo al SO del granito de La Maladeta probablemente está relacionado con las acumulaciones de evaporitas triásicas.

The GeoPiri3D project aims to characterize the geometry and kinematics of the Permo-Carboniferous batholiths of the Central Pyrenees through a combination of potential fields and structural data. During 2018 we have acquired 824 new gravity stations and 186 rock samples. The gravity data were processed and integrated into the IGME database and a new Bouguer anomaly was calculated. The two main granite bodies (La Maladeta and Andorra-Mount Louis) provide different gravimetric responses. The anomaly on the La Maladeta granite outcrop presents a zonation with small variations in its amplitude. The petrophysical data provide an average density of ca. 2.6 g/cm3, which is consistent with its granodioritic composition. The outcrop of the Andorra-Mount Louis pluton is characterized by a relative minimum, suggesting a dominant granitic composition. In addition, the minimum extends in an oblique NE direction indicating that part of the pluton is buried. The relative minimum to the SW of La Maladeta is probably linked to accumulations of Triassic evaporites.

The South Pyrenean triangle zone represents the southernmost front of the Pyrenees at its central portion deforming the Upper Eocene-Miocene Ebro Basin deposits. Two main structures characterize its western termination, the Barbastro anticline and the San Román backthrust, which detached on the Barbastro Formation (and lateral equivalents), an Upper Eocene-Lower Oligocene syntectonic evaporite-rich formation that acted as a multidetachment unit. Northward, the south directed Pyrenean thrust unit (i.e., Gavarnie-Sierras thrust sheet) detached along the Middle-Upper Triassic evaporitic rocks to finally ramp up and glide along the same Upper Eocene-Lower Oligocene multidetachment unit. A multidisciplinary approach allowed constructing a detailed structural and stratigraphic model of the study area. The workflow consisted of (1) constraining the geometry and structural architecture based on surface geology, interpretation of seismic lines (>900 km), and wells and (2) obtaining the 3-D density distribution of the multidetachment unit using gravity stochastic inversion (more than 7, 000 gravity stations and 1, 500 density data). The geometry of the sole thrust of the Gavarnie-Sierras thrust sheet was controlled by the distribution of the evaporite-rich units of the Barbastro Fm. Weak detachments promoted thrust salient formation and thrust flat geometries. The western termination of the South Pyrenean triangle zone is defined as a westward transition from a ramp-dominated and multiple triangle zone to a detachment-dominated one. Its geometry, kinematics, and location were controlled by the heterogeneous lithology of the Barbastro Fm. and its basal, halite-based detachment southern pinch-out.

In this work, we present new Bouguer and residual Bouguer anomaly maps of the Central Pyrenees calculated from 3590 stations, of which 1141 are new observations acquired from surveys performed between 2018 and 2019. The most prominent feature of the Bouguer anomaly is the long wavelength elongated minimum in its central part that continues to the W and ends towards the E with a positive gradient that seems to envelope the minimum. Other short and medium wavelength minima are superimposed, some placed over the batholithic outcrops. In the residual Bouguer, the main relative minima are related with outcrops of batholiths or interpreted buried granites except for the prominent minimum South of La Maladeta Granite, associated with Triassic evaporitic accumulations. These maps (shown on the Main Map) will help characterizing the Permo-Carboniferous batholiths of the Central Pyrenees, in particular La Maladeta and Andorra Mont-Louis granites in order to add constraints to the mechanism of their emplacement.

The aim of this work is the application of the anisotropy of magnetic susceptibility (AMS) to the study of volcanic materials from the Late Carboniferous-Permian Cadí basin (southern Pyrenees) in order to (i) explore the limits of this technique in ancient volcanic materials that have undergone strong chemical alteration and a complex tectonic evolution and (ii) provide new insights on the deposition of volcanic materials in this tectonically controlled sedimentary basin. To establish a comparison with the petrofabric of rocks, AMS was complemented with observations and orientation analyses at the outcrop scale, in oriented polished blocks and in thin sections under the microscope. High resolution sampling (620 specimens from 56 sites located in five transects along a sequence 150 m thick) allowed to characterize the volcaniclastic and lava flow series. The AMS results show a fairly constant average magnetic lineation oriented WNW-ESE (in situ and tilt-corrected) and two secondary maxima (N-S to NE-SW in some areas). The magnetic mineralogy analyses indicate the contribution of paramagnetic and ferromagnetic (magnetite, Tc 580 °C) phases to susceptibility. The magnetic fabric has a close relationship with the spatial distribution and orientation of the mineral and grain components of the studied rocks, mainly controlled by depositional processes, with a negligible contribution of the tectonic imprint. Therefore, the magnetic lineation (i.e. K1 axes) can be reliably used as a paleoflow indicator. Nevertheless, it was not possible to establish a clear correspondence between lithological and magnetic fabric types. The results obtained indicate that the AMS approach represents a powerful tool to infer the paleoflow pattern in ancient volcanic and volcaniclastic rocks, even under a priori unfavourable conditions.

In this work we establish reliable correlations between density and magnetic susceptibility in three paramagnetic granites from the Pyrenees. In total, 128 sites (310 density measurements and >2600 susceptibility ones) were studied in the Mont Louis-Andorra, Maladeta and Marimanha granitic plutons covering the main range of variability of magnetic susceptibility. Regressions were calculated for every granitic body and an integrated linear function was obtained for the entire dataset: \u03c1 (kgm3) = 2566 (kgm3) + 0.541\u03ba (10\u22126 S.I.) (R:0.97). This relationship is only valid in the paramagnetic domain, where iron is mostly fractioned in iron-bearing phyllosilicates and the occurrence of magnetite is negligible (or at least its contribution to the bulk susceptibility). This relationship, likely different in other bodies, allows for transforming magnetic susceptibility data into density data, helping to constrain gravity modelling when density data from rock samples are scarce. Given the large amount of AMS studies worldwide, together with the quickness and cost-effectiveness of susceptibility measurements with portable devices, this methodology allows for densifying and homogenizing the petrophysical data when modelling granite rock volumes based on both magnetic and gravimetric signals.

A new gravity survey (1164 gravity stations and 180 samples for density analysis) combined with two new geological cross sections has been carried out in a sector of the Central Pyrenees in order to improve the characterization of basement and cover architecture. From North to South, the study area comprises the southern half of the Axial Zone and the northernmost part of the South-Pyrenean Zone. New gravity data were combined with previous existing databases to obtain the Bouguer and residual anomaly maps of the study area. The two cross sections, oriented NNE–SSW, were built from field data and previous surficial and subsurface data and cross the La Maladeta plutonic complex. The residual anomaly map shows values ranging from -18 to 16 mGal and anomalies mainly oriented N120E. The two 2.5D modelled cross sections show similar observed gravity curves coinciding with similar interpreted structural architecture. Data show a gravity high oriented N120E coinciding with the Orri basement thrust sheet and an important gravity depression, with the same orientation, coinciding with the leading edge at depth of the Rialp basement thrust sheet and interpreted as linked to a large subsurface accumulation of Triassic evaporites. The volume at depth of the La Maladeta and Arties granites has been constrained through gravity modelling. This work highlights that the combination of structural geology and gravity modelling can help to determine the structural architecture of an orogen and localize accumulations of evaporites at depth. © 2021, The Author(s).