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

Gravity data on the Central Pyrenees: a step forward to help a better understanding of the Pyrenean structures http://hdl.handle.net/10261/256413, This database corresponds to the new Bouguer and residual Bouguer anomaly gravity data of the Central Pyrenees calculated from 3588 stations, of which 1140 are new observations acquired from surveys performed between 2018 and 2019.
The processing, calculations and interpretations can be found in Gravity data on the Central Pyrenees: a step forward to help a better understanding of the Pyrenean structures (Ayala et al., 2020, DOI … ).
Please note that there is a difference of one data from this database respect the number that appears on the paper. This is due to the identification of a duplicated point after the publication of the paper. The duplicated point has been deleted from this database., This database is part of the project CGL2017-84901-C2-2-P funded by MCIN/AEI/10.13039/501100011033 and "ERDF A way of making Europe", 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 Parc Natural de l’Alt Pirineu is located
between the La Maladeta and Andorra-
Mount Louis granites. The characterization
of the Parc’s geology at depth can help to
know the emplacement mechanism of these
granites, their relationships with the plutonic
and volcanic rocks outcropping to the North
and South of the Parc, respectively, and if all
these rocks belong to the same magmatic
system.
To achieve these objectives, in the frame
of the present research project, we have
compiled and homogenezed previous
gravimetric and magnetic data, and
acquired new geophysical data, in particular,
gravity data. We have also constructed
new geological cross-sections oriented
NE-SW from previous and new acquired
geological data and characterized the
petrophysical properties of the geological
units in order to obtain the density and
magnetic susceptibility of all different
rocks outcropping in the study area. The
geological cross-sections together with the
petrophysical data will be used in the 2,5
and 3D gravimetric modelling to improve our
understanding of the subsurface geology of
this part of the Central Pyrenees and of the
Parc Natural de l’Alt Pirineu., El Parc Natural de l’Alt Pirineu se encuentra
en la zona situada entre el granito de La
Maladeta y el granito de Andorra-Mount
Louis. Conocer y entender la geología del
subsuelo del Parc nos ayudará a saber
cómo se produjo el emplazamiento de
ambos macizos graníticos, su relación
con las rocas plutónicas y volcánicas que
afloran en la parte norte y sur del Parc,
respectivamente, y si forman parte de un
mismo sistema magmático.
Para alcanzar estos objetivos, se
está realizando una recopilación y
homogeneización de datos gravimétricos
y magnéticos ya existentes, así como la
adquisición de nuevos datos geofísicos,
en particular de gravimetría. Además,
partiendo de estudios geológicos previos
y datos propios, se está llevando a cabo
la realización de cortes geológicos de
dirección NE-SO y el estudio petrofísico
de las unidades geológicas para obtener
los valores de densidad y susceptibilidad
magnética de todos los tipos de rocas que
afloran en el área de estudio. Los cortes
geológicos junto con los datos de petrofísica
se utilizarán en la modelización gravimétrica
2,5D y 3D para mejorar la interpretación de
la geología del subsuelo en este sector de
II Jornades de Recerca del Parc Natural de l‘Alt Pirineu 87
los Pirineos Centrales y del Parc Natural de
l’Alt Pirineu., Este trabajo se está llevando a cabo en el marco de los subproyectos CGL2017-84901-C2-1 y CGL2017-84901-C2-2-P del Ministerio de Ciencia, Innovación y Universidades. Los desarrollos metodológicos en exploración con técnicas geofísicas se encuentran alineados con el proyecto europeo 3DGeoEU- GeoERA (ERANET Cofund action 731166 [H2020], Project code GeoE.171.005). Los autores agradecen al Parc Natural de l’Alt Pirineu las facilidades prestadas y la organización de las jornadas de investigación para mostrar los trabajos realizados.

Major challenges in volcanology are the abilities to recognise if, when and how fast magmatic systems can switch from states of dormancy into states of unrest or eruption. Despite an increasingly large body of geophysical information on magma migration and accumulation within magma plumbing systems, there are currently no integrated views on how mush-dominated magma plumbing systems evolve in space and time, how magma is stored, transferred and processed within these systems and how mush processes affect the behaviour, duration and intensity of volcanic eruptions. This is particularly critical as mush processes can perturb seemingly dormant or steady-state volcanoes, leading to dramatic changes in behaviour. Thus, understanding the dynamics of mush-to-magma conversion is not only important for describing the physical evolution of magma plumbing systems, but is also vital for carrying out effective volcano monitoring and risk assessment.

In this session we welcome contributions that use the physical and chemical properties of volcanic eruption products, and those of crystals in particular, to improve our understanding of mush-bearing magma plumbing systems. We especially welcome contributions that focus on critical timescales of magma storage, re-mobilisation and transfer within mush-bearing systems as well as those that investigate and compare rates of mush-to-magma conversion in chemically distinct systems. We also invite contributions that exploit recent improvements in analytical, experimental and computational techniques to extract P-T-t-X conditions of mush processes more generally. Contributions that consider the implications of mush-to-magma conversion for volcano monitoring and risk assessment are also highly welcome.
The volcanic-plutonic connection has been postulated mostly based on indirect evidence coming from geochemical, petrological, and geophysical approaches, and theoretical modelling. However, very few direct field examples of such connection have been offered. The reason is that most well exposed volcanic terrains are so young for erosion or tectonics to have exhumed their deeper plutonic roots, while plutonic terrains are too old to preserve possible coeval volcanic equivalents. The Pyrenees, an Alpine mountain range located between Spain and France, offers an exception to this general rule, and exposes co-genetic and coeval plutonic, subvolcanic and volcanic rocks that offer good field evidence of the existence of such plutonic-volcanic connection. A significant portion of the continental crust ranging in age from the Cambro-Ordovician to Permian, exposes two examples of such connection corresponding to the upper Ordovician and the Upper Carboniferous-Lower Permian magmatic episodes. In both cases, volcanic rocks are the eruptive expression of these magmatic episodes, which also generated large plutonic bodies and subvolcanic dyke complexes emplaced at very sallow depths. The field-based stratigraphic and structural reconstruction of some of these plutonic-subvolcanic-volcanic complexes, as well as new zircon U-Th radiometric ages and petrological and geochemical data, demonstrate that there was a time-space and genetic relationship between them, thus offering one of the scarce direct evidence of the existence of the so many times postulated but still not clearly proved plutonic-volcanic connection., This research is supported by MINECO grant SIMPROP (CGL2017-84901-C2)

El empleo de métodos de campo potencial en la exploración geofísica, en especial la gravimetría,
es una herramienta clásica para el estudio del subsuelo y viene siendo utilizada ampliamente
desde principios del S. XX (para una visión histórica más amplia ver LaFerh, 1980). El primer
gravímetro moderno fue desarrollado por LaCoste & Romberg en 1936 quienes inventaron la
mayoría de los refinamientos posteriores. Desde entonces el desarrollo de los gravímetros, cada
vez más portables y precisos, ha permitido la aplicación de este método en un amplio rango de
objetivos que incluyen la investigación en recursos naturales (hidrocarburos, minería,
geotermia, hidrogeología, etc.), estudios superficiales de detalle (detección de cavidades,
arqueología, caracterización de reservorios), investigación básica (caracterización tanto de las
estructuras del basamento y la corteza superior como de toda la litosfera), apoyo a la cartografía
geológica proporcionando información de geología no aflorante que ayude al entendimiento de
la geología regional (p. ej. apoyo a los cortes geológicos), etc., La obtención de los ejemplos aportados en este documento ha sido posible gracias a los
siguientes proyectos de financiación pública (nacional y europea):
- Establecimiento de bases metodológicas para la obtención de Cartografía Gravimétrica
1:50000. Aplicación a la modelización 2D y 3D en varias zonas de la Península Ibérica (IGME
2005). Fondo documental del IGME, informes nº: 64058, 64059, 64060, 64061, 64062,
64063 y 64064. http://info.igme.es/ConsultaSID/Index.asp.
- High-resolution imaging of the crustal-scale structure of the Central Pyrenees and role of
Variscan inheritance on its geodynamic evolution (IMAGYN) (Proyecto de I+D+I PID2020-
114273GB-C22 financiado por MCIN/AEI/10.13039/501100011033).
- Caracterización 2.5 y 3D de la estructura cortical del Pirineo Catalán con especial atención
a los cuerpos graníticos y cuencas volcano-sedimentarias permocarboníferas (GeoPiri3D)
(Proyecto de I+D+i CGL2017-84901-C2-2-P financiado por
MCIN/AEI/10.13039/501100011033 y "FEDER, una manera de hacer Europa").
- Unravelling the kinetics of burial remagnetizations; an integrated 4D approach (UKRIA4D)
(Proyecto de I+D+I PID2019-104693GB-I00 financiado por
MCIN/AEI/10.13039/501100011033 y "FEDER, una manera de hacer Europa").
- 3D geomodeling for Europe-Optimizing reconstructions of the subsurface to reduce
structural uncertainty in 3D models (GeoERA-3DGEO-EU). Proyecto financiado por ERANET
CA 731166 (H2020) de la Unión Europea (Project code GeoE.171.005).
- Research network for including Geothermal technologies into Decarbonized Heating and
Cooling grids Geothermal DHC (CA18219/ OC-2018-2-23361).
- Detachment folds and diapirs; recognition, reconstruction, restoration advanced
methodologies (DR3AM) (CGL2014-54118-C2-2-R).
- Consistent 3D restoration in complex structures by using structural and paleomagnetic 3D
references Pmag3DRest (CGL2009-14214-BTE).
- Geociencias en Iberia: Estudios integrados de topografía y evolución 4D. Topo-Iberia.
(CGL2010–15416). SiTopo Base de datos de Topo-Iberia (acceso controlado)., 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).