Basement structure of the Hontomín CO2 Geological storage facility (Burgos, Spain): integration of microgravity & 3D seismic reflection data

The structure of the Hontomín CO2 geological storage research facility has been addressed combining 3D seismic reflection data, borehole information and microgravity data. The integrated interpretation constrains the basement structural setting geometry and that of the sedimentary succession. The study unravels the deep structure and topography of the basement and quantifies the thickness of the Triassic Keuper evaporites. We describe a half-graben setting filled with Keuper evaporites (up to 2000 m) forming an extensional forced fold. Three set of faults are identified with two main fault systems compartmentalizing the area into three differentiated blocks. These faults have been interpreted to be reactivated normal faults that have led to the formation of the Hontomín dome.The datasets in this work have been funded by Fundación Ciudad de la Energía (Spanish Government, www.ciuden.es) and by the European Union through the “European Energy Programme for Recovery” and the Compostilla OXYCFB300 project. Dr. Juan Alcalde is currently funded by NERC grant NE/M007251/1.Peer Reviewe

Basement structure of the Hontomín CO2 Geological storage facility (Burgos, Spain): integration of microgravity & 3D seismic reflection data

The structure of the Hontomín CO2 geological storage research facility has been addressed combining 3D seismic reflection data, borehole information and microgravity data. The integrated interpretation constrains the basement structural setting geometry and that of the sedimentary succession. The study unravels the deep structure and topography of the basement and quantifies the thickness of the Triassic Keuper evaporites. We describe a half-grabensetting filled with Keuper evaporites (up to 2000 m) forming an extensional forced fold. Three set of faults are identified with two main fault systems compartmentalizing the area into three differentiated blocks. These faults have been interpreted to be reactivated normal faults that have led to the formation of the Hontomín dome.The datasets in this work have been funded by Fundación Ciudad de la Energía (Spanish Government, www.ciuden.es) and by the European Union throughthe “European Energy Programme for Recovery” and the Compostilla OXYCFB300 project. Dr. Juan Alcalde is currently funded by NERC grant NE/M007251/1.Peer Reviewe

El Perfil sísmico ALCUDIA: una imagen de la Zona Centroibérica (Varisco Ibérico meridional, España)

The 250 km long, vertical incidence seismic reflection profile ALCUDIA was acquired in spring 2007. It samples the Variscan Central Iberian Zone from Toledo to Fuenteovejuna. Its main goal was to continue the structure obtained for the crust and mantle from the IBERSEIS transect towards the N and NE. The acquisition parameters, similar to those used in the IBERSEIS profile have proven to be adequate to show a detailed image of the whole crust and upper mantle. After preliminary processing, the upper crust shows a moderate reflectivity that can be easily correlated with identifiable surface geologic features. The middle and lower part of the crust seems to be very reflective, laminated and afected by deformation, although to a different extent. The Moho is placed at approximately 10 s TWT and appears to be flat in the time section. The section can be divided into four domains of reflectivity that can be key to stablish different domains of crustal evolution. This new transect, together with the previous IBERSEIS profile, complete an almost 600 km long lithospheric section that crosses the southern half of the Iberian Variscides.El perfil sísmico de reflexión ALCUDIA , de 250 km de longitud, fue adquirido en la primavera del año 2007. Este perfil ha muestreado la Zona Centroibérica entre Toledo y Fuenteovejuna, y su objetivo principal ha sido continuar hacia el NE la estructura de corteza y manto ya obtenida mediante el perfil IBERSEIS. Los parámetros de adquisición, similares a los de IBERSEIS, han sido adecuados para mostrar una imagen detallada de toda la corteza y el manto superior. Una vez efectuado el procesado preliminar, la corteza superior presenta una reflectividad moderada que puede correlacionarse fácilmente con rasgos geológicos de superficie. Las partes media e inferior de la corteza son muy reflectivas, laminadas y afectadas por una deformación que varía a lo largo del perfil. La Moho se localiza a unos 10 s TWT y tiene geometría plana en la sección de tiempo. La variación en los patrones generales de reflectividad permite dividir el pefil sísmico en cuatro dominios, que corresponden a diferentes evoluciones corticales. Este nuevo perfil sísmico, unido al anterior perfil IBERSEIS, constituye una sección litosférica de casi 600 km de longitud, que atraviesa la parte meridional del Varisco Ibérico.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Ciencia e Innovación (MICINN)Generalitat de CatalunyaJunta de Comunidades de Castilla La Mancha.pu

Petrophysical characterization of non-magnetic granites; density and magnetic susceptibility relationships

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 reviewe

Density and magnetic susceptibility relationships in non-magnetic granites; a “wildcard” for modeling potential fields geophysical data

EGU2020: Sharing Geoscience Online, 4-8 May 2020Geophysical surveying (both gravity and magnetic) is of great help in 3D modeling of granitic bodies at depth. As in any potential-field geophysics study, petrophysical data (density [r], magnetic susceptibility [k] and remanence) are of key importance to reduce the uncertainty during the modeling of rock volumes. Several works have already demonstrated that ¿18O or [SiO2] display a negative correlation to density and to magnetic susceptibility. These relationships are particularly stable (and linear) in the so-called ¿non-magnetic¿ granites (susceptibilities falling within the paramagnetic range; between 0 and 500 10-6 S.I.) and usually coincident with calc-alcaline (CA) compositions (very common in Variscan domains). In this work we establish robust correlations between density and magnetic susceptibility at different scales in CA granites from the Pyrenees. Other plutons from Iberia were also considered (Veiga, Monesterio). The main goal is to use the available and densely sampled nets of anisotropy of magnetic susceptibility (AMS) data, performed during the 90¿s and early 2000¿s, together with new data acquired in the last few years, as an indirect measurement of density in order to carry out the 3D modelling of the gravimetric signal. We sampled some sections covering the main range of variability of magnetic susceptibility in the Mont Louis-Andorra, Maladeta and Marimanha granite bodies (Pyrenees), all three characterized by even and dense nets of AMS sites (more than 550 sites and 2500 AMS measurements). We performed new density and susceptibility measurements along two main cross-sections (Maladeta and Mont Louis-Andorra). In these outcrops, numerous measurements (usually more than 50) were taken in the field with portable susceptometers (SM20 and KT20 devices). Density data were derived from the Arquimedes principle applied on large hand samples cut in regular cubes weighting between 0.3 and 0.6 kg (whenever possible). These samples were subsampled and measured later on with a KLY-3 susceptibility bridge in the laboratory. Additionally, some density data were derived from the geometry and weighting of AMS samples. After the calibration of portable and laboratory susceptometers, density and magnetic susceptibility were plotted together. Regressions were derived for every granite body and they usually followed a linear function similar to: r = 2600 kg/m3 + (0.5 * k [10-6 S.I.]). As previously stated, this relationship is only valid in CA and paramagnetic granites, 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). These relationships allow transforming magnetic susceptibility data into density data helping in the 3D modelling of the gravimetric signal 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 densifying and homogenizing the petrophysical data when modelling granite rock volumes based on both magnetic and gravimetric signal

Estudio de las rocas paleozoicas y los macizos graníticos que afloran en el Parc Natural de l'Alt Pirineu y zonas colindantes mediante datos geológicos, geofísicos y petrofísicos

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

Petrophysical properties in the Iberian Range and surrounding areas (NE Spain): 1-density

Pueyo, E.L. et. al.We introduce the first map of density data in Northeastern Spain which can help in the interpretation of gravimetric surveying. The background map is a simplified version of the Geode continuous geological cartography (scale 1:200.000) of the Iberian Range and Ebro basin. These maps are synthetic and homogeneous maps based on previous 1:50,000 scale geological maps (MAGNA). The map uses the ETRS89 datum and UTM coordinates (30T northern zone) and covers an area of 140,000 sq km. The compiled data shown in the map come from previous papers of the region (≈ 700 points) as well as from more than 800 additional points developed in the course of an exploratory project focused on the underground characterization of a potential CO2 reservoir in the so-called ‘Linking Zone'. The new data accomplish some basic criteria; they are accurately georeferenced and lithology, stratigraphic age and other technical details about the measurements (e.g. means and error) and methods are fully displayed.Peer reviewe