Polyorogenic structure of the San Rafael Block, Mendoza, Argentina: New data for the interpretation of the Chanic Orogen

The Paleozoic pre-Carboniferous rocks of the San Rafael Block, located to the east of the Los Reyunos Gondwanan Thrust, show Chanic structures (Late Devonian–early Carboniferous) with east vergence, which were generated in the absence of metamorphism. This Paleozoic succession is unconformably located on the basement of Cuyania. The rocks, located to the west of the Los Reyunos Thrust, were deformed by two fold episodes, the first and main (D1) west verging, developed under low to very low-grade metamorphic conditions, and the second (D2) east verging and mainly developed near Los Reyunos Reservoir. Therefore, the Los Reyunos Thrust must be considered a reactivation of a Chanic structure during the Gondwanan Orogeny (late Carboniferous–early Permian). The ancient Chanic thrust could be responsible for the overlay of the hinterland of the western branch of the Chanic Orogen on the foreland of its eastern branch, at the end of the collision between the Cuyania and Chilenia subplates. The results of this work have been related to those of nearby areas located to the north and west, which has allowed the elaboration of a model that explains the characteristics of the Chanic Orogen in this area. During the Carboniferous, the Los Reyunos Thrust was reactivated as a normal fault, facilitating the sedimentation of carboniferous rocks thousands of meters thick in its hanging wall and later, during the Gondwanan deformation, it underwent a tectonic inversion. During the Andean cycle, the Permian–Triassic beds of the Choiyoi Group were deposited in relation to NW–SE trending normal faults, giving rise to rollover structures. Finally, during the Cenozoic, Andean compression gave rise to the formation of an open antiform, in whose core is the Mesoproterozoic–Paleozoic basement of the San Rafael Block.Facultad de Ciencias Naturales y Muse

Assessing the internal uppermost crustal structure of the central pyrenees by gravity-constrained cross sections

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 reviewe

High-resolution scan of the Pyrenean crustal structure combining magnetotelluric and gravity data

The Pyrenees have undergone complex geodynamic evolution starting with experiencing significant tectonic events during the Variscan Orogeny, followed by the intrusion of large granitic complexes during the late Variscan stage, then the collision between the Iberian and European plates during the Alpine Orogeny, and finally, Mesozoic extension. Despite extensive studies and the application of various geophysical methods (two-dimensional seismic reflection data, gravity, and long period magnetotellurics) to investigate the Pyrenean structure, there are still fundamental questions regarding its basement and cover architecture. Specifically, the geometry at depth of significant bodies such as the Late Variscan intrusive granites and Triassic evaporitic accumulations, remains unclear. To better understand these issues, we have conducted joint magnetotelluric and gravity surveys along a 60-kilometer-long transect, spanning the boundary between the Axial and South Pyrenean Zones. Our final geological interpretation shows that the La Maladeta batholith consists of two distinct granitic bodies related to different intrusive pulses. In addition, we identify important Triassic evaporitic accumulations at depth. This work shows the high potential of integrating two geophysical models for understanding the geological evolution of structurally complex areas. The magnetotelluric and gravity data are complementary, with each dataset providing a different resolution for investigating the basement and cover architecture of the Pyrenees. These resolutions depend on the varied petrophysical properties of the rocks involved, including water content and deformation grade

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

Variaciones laterales en el basamento y cobertera de los Pirineos Centrales

La deformación Alpina en los Pirineos Centrales dio lugar a un cinturón de pliegues y láminas de cabalgamiento que involucran al basamento paleozoico y a la cobertera mesozoico-cenozoica, esta última despegada sobre las evaporitas del Triásico. La zona de estudio abarca la mitad meridional de la Zona Axial, desde el granito de la Maladeta al oeste hasta el granito de Andorra-Mont Louis al este, así como la parte más septentrional de la Zona Surpirenaica. Este trabajo tiene como objetivo analizar las variaciones laterales de la estructura del subsuelo de la zona de estudio, en base a la estructura ya establecida a partir de trabajos geológicos y geofísicos previos. Para ello se han elaborado seis cortes geológicos seriados partiendo de dichos trabajos, de cartografías geológicas previas e introduciendo datos propios; también se ha llevado a cabo la recopilación y homogenización de los datos gravimétricos existentes (base de datos SITOPO (proyecto TopoIberia) y base de datos del ICGC), y la adquisición de más de 1000 nuevos datos; finalmente se han realizado 231 medidas de densidad de todas las litologías que afloran en el área estudiada. Todo ello para elaborar los mapas de anomalías de Bouguer y anomalía gravimétrica residual de la zona, así como la modelización gravimétrica 2.5 D de los cortes geológicos realizados. Los mapas gravimétricos y los cortes seriados obtenidos permiten observar variaciones laterales relacionadas con (i) la existencia o no de rocas evaporíticas, (ii) variaciones de la geometría en profundidad de los cuerpos ígneos tardi-variscos y (iii) variaciones laterales en la geometría de las láminas de cabalgamiento alpinas que involucran al basamentoThe Alpine deformation in the Central Pyrenees generated a fold-and-thrust belt involving Paleozoic basement and decou- pled Mesozoic-Cenozoic cover units detached on the main décollement level located in the Triassic evaporites. The study area comprises the southern sector of the Axial Zone from la Maladeta granite in the west to the Andorra-Mont Louis granite to the east as well as the northernmost part of the South Pyrenean Zone. The goal of this work is to analyse lateral varia- tions of subsurface structure of the study area, which was established based on previous geological and geophysical works. With this aim, six serial geological cross sections were built using available geological maps and previous published works together with new data. More than 1000 new gravity stations were acquired and harmonized together with available data from SITOPO database (TopoIberia project) and ICGC database as well as 231 new density measurements taken from all rock types outcropping in the study area. Integration of all this information allowed us to calculate the Bouguer and residual gravity anomaly maps and to carry out 2.5 D gravity modelling along the six cross sections. Both, maps and cross sections, show lateral variations related to (i) occurrence or absence of Triassic evaporites, (ii) different geometry at depth of the Late Variscan igneous bodies and (iii) geometric lateral changes of the alpine basement-involved thrust sheet

Nuevos datos gravimétricos y geológicos de la Zona Axial y límite con la Zona Surpirenaica del Pirineo Central

El conocimiento de la geometría del subsuelo se basa en la integración de datos geológicos y geofísicos. En la Zona Axial del Pirineo Central y sector septentrional de la Zona Surpirenaica, la ausencia de perfiles de sísmica de reflexión dificulta esta labor y hace necesaria la búsqueda de otras técnicas, como la gravimetría, para inferir su estructura en profundidad. En este trabajo los equipos del IGME e ICGC han tomado 1164 nuevas estaciones gravimétricas en la zona de estudio, se han recopilado 2740 estaciones previas de las bases de datos de SITOPO (proyecto TopoIberia) e ICGC y se ha realizado su homogenización. Se ha obtenido un nuevo mapa de la anomalía de Bouguer caracterizado por un mínimo elongado de longitud de onda larga de más de -100 mGal asociado a la raíz cortical de los Pirineos. Cabe destacar la diferente respuesta gravimétrica que ofrecen los dos principales granitos de la zona de estudio, La Maladeta y Andorra-Mont Louis (menor densidad que las rocas Paleozoicas del encajante). Al SO del granito de La Maladeta aparece un mínimo relativo que se interpreta asociado a acumulaciones evaporíticas triásicas (menor densidad) en profundidad. Además se ha realizado: (i) un mapa de anomalía residual asumiendo una anomalía regional correspondiente a un polinomio de tercer grado para inferir la estructura más superficial y (ii) mapas de las derivadas vertical y horizontal de la anomalía gravimétrica residual para observar cómo varían espacialmente los valores de densidad de las rocas existentes. Este trabajo destaca el potencial de la gravimetría en el estudio de la estructura en profundidad de orógenos y cinturones de pliegues y cabalgamientos con presencia de rocas ígneas y/o evaporíticas con valores de densidad menores al de las rocas sedimentarias encajante

Towards 3D databases and harmonized 3D models at IGME-CSIC

IGME-CSIC has a highly relevant geological and geophysical database that includes a continuous digital geological cartography at 1:50000; 1:200000 and 1:1000000 scales and a fair amount of geophysical data: gravity, magnetic, well-logs in tiff and LAS format, seismic lines in tiff and SEG-Y format, borehole and petrophysical data, together with other geophysical and geological studies. Since the 2004, an important effort has been done to undertake 3D geological and geophysical modelling ranging from local studies (mineral exploration or CO2 storage sites) to regional geology for a better understanding of the subsurface structure and its geodynamic evolution as a base for other studies on natural hazards or mineral resources. These studies were ¿stand alone¿ and now IGME is designing a new strategy. It includes the available data and models harmonization (stratigraphy sequences, structural interpretations, faults distribution, seismic velocity models, spatial distribution of physical properties such as density and magnetic susceptibility, workflows, methodologies, evaluation of uncertainties, visualization, etc.) to comply with the FAIR (Findable, Accessible, Interoperable and Reusable) data standardization. In this way, the new 3D models will be easily integrated and available from the databases. This strategy includes collaboration with the Bureau de Recherches Géologiques et Minières of France (BRGM) and Laboratório Nacional de Energia e Geologia of Portugal (LNEG) in order to harmonize the Spanish geological data and models with their neighbours across national borders. The first step is being done in the framework of GeoERA projects. Plain-language Summary IGME-CSIC owns a large database that includes a highly valuable geological and geophysical data and geophysical studies containing the interpretation of some of the data of Spain (onshore and offshore) Since 2004 the authors of this work have been working in 3D geological and geophysical modelling that includes local (mineral exploration or CO2 storage sites) and regional studies. The goal is to improve our understanding of the subsurface structures and processes as a base for deepening our knowledge in how the natural hazards occur, how to improve the exploration for mineral resources, etc. These studies were made ad hoc within different projects and now IGME-CSIC is designing a workflow to harmonize these models in order to comply with the FAIR (Findable, Accessible, Interoperable and Reusable) data standardization so the models will be available to being used beyond the initial objectives that generated their creation. This strategy includes collaboration with other European institutions like the Bureau de Recherches Géologiques et Minières of France (BRGM) and Laboratório Nacional de Energia e Geologia of Portugal (LNEG) in order to harmonize the models across national borders. The first step is already being done in the framework of the GeoERA projects

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

Characterization of the Cerdanya Neogene Basin by combining geophysical methods: passive seismic, magnetotelluric and gravimetry.

Congreso realizado en Toledo del 28 de noviembre al 1 de diciembre de 2022.[EN] The Cerdanya Neogene basin, located in the eastern sector of the Central Pyrenees, has been studied to characterize its structure in depth. The thickness of the Neogene filling of the basin (detrital materials with some levels of lignite) has been inferred by combining different geophysical exploration methods in a NW-SE trending profile that crosses, perpendicularly, the basin in its central part: passive seismic (H/V spectral ratio method and array technique), electromagnetic methods (MT and AMT) and gravimetry. Applying the array technique, the shear wave velocity (Vs) of the basin materials has been calculated, both for the Neogene deposits and the bedrock. These data combined with the results obtained from the H/V spectral ratio method allow deriving the bedrock geometry. The electromagnetic method provides the 2D electrical resistivity model, characterizing the geoelectric properties of the basin and depicting the presence of the d'Alp-la Tet fault, an important structural element of the basin. The electrical model inversion uses as an initial model the bedrock depth obtained from the passive seismic. In the residual Bouguer anomaly modelling, a satisfactory gravimetric model is obtained when the thickness of the Neogene deposits varies between 0 and 650 meters and assigned density of 2.2 g/cm3 , supported by the low Vs obtained. The thickness of the Neogene filling presents variations that are related to the presence of normal fault with small vertical offset. The application of this methodology, based on the combination of different geophysical exploration methods, has reduced the different uncertainties inherent in each geophysical method, and aim to characterize the Cerdanya Neogene basin geometry.Este trabajo se ha financiado con el proyecto PID2020-114273GB-C22 financiado por MCIN/AEI/10.13039/501100011033 del Ministerio de Ciencia e Innovación de España.Peer reviewe

Orogenias paleozoicas en los Andes de Argentina y Chile y en la Península Antártica

Congreso Geológico Argentino (20º. 2017. San Miguel de Tucumán, Argentina). Simposio de Téctonica pre-andinaDurante el Neoproterozoico y Paleozoico, los Andes de Argentina y Chile, y desde fines del Paleozoico también la Península Antártica, formaron parte del margen SO de Gondwana. Durante este tiempo se acrecionaron a dicho margen varios fragmentos continentales de tamaño y aloctonía variable; denominados de N a S: Antofalla, Chi-Cu, Patagonia Occidental y Antártida Occidental. Estos fragmentos formaban parte de placas litosféricas, en ocasiones divididas en subplacas. La colisión de dichos fragmentos continentales con Gondwana y una última subducción bajo dicho margen, dieron lugar a 6 orogenias de extensión temporal y espacial limitada.Instituto Geológico y Minero de España, EspañaDepartamento de Geología, Universidad de Oviedo, EspañaUniversidad de Río Negro, ArgentinaServicio Geológico y Minero Argentino, ArgentinaInstituto De Bio y Geociencias Del NOA, Consejo Nacional de Investigaciones Científicas y Técnicas, ArgentinaInstituto De Bio y Geociencias Del NOA, Universidad Nacional de Salta, ArgentinaDepartamento de Geodinámica, Universidad del País Vasco, EspañaFacultad de Geología, Universidad de Barcelona, EspañaDepartamento de Geología, Universidad de Chile, ChileUniversidad Andrés Bello, ChileUnidad de Tectónica, Consejo Nacional de Investigaciones Científicas y Técnicas, ArgentinaFacultad de Geología, Universidad de Buenos Aires, ArgentinaÁrea de Geología, Universidad Rey Juan Carlos, EspañaUniversidad de Salta, ArgentinaInstituto de Investigación en Paleobiología y Geología, Universidad de Río Negro, ArgentinaInstituto de Investigación en Paleobiología y Geología, Consejo Nacional de Investigaciones Científicas y Técnicas, ArgentinaCentro de Investigaciones Geológicas, Universidad de La Plata, ArgentinaUniversidad de San Juan, ArgentinaPeer reviewe