Pantelleria is a 84 km² extended volcanic island located in the Mediterranenan Sea between Sicily (Italy) and Tunisia. Previous studies described that in Pantelleria island both tectonic structures and the volcano-tectonic features had a common tectonic origin controlled by a NW-SE directed extension in accordance with the regional trend of the Sicily Channel arising interest for multiapproach investigations.

Indeed, in the last decades this area has been field of widespread analysis useful for the investigation of the volcano-tectonic and tectonic activity, as well as for geodetic study and resources exploration.

Our approach focused on the gravimetric analysis of Pantelleria island and in particular we provided a 3D inverted model of the area, starting from in-situ gravity measurements. The 250 m model resolution has been endorsed by the presence of a total of  290 measurement stations, distributed both onshore and offshore and acquired during some field surveys up to 2006; 236 of them were already published and inverted in past using 2.5D modelling. Input data consisted of a database containing Bouguer anomaly data reduced using a  density of 2500 kg/m³ and referred to the Geodetic Reference System 1980 (GRS80) Ellipsoid.

As a result, the 3D modelling allowed exploring density differences through the about 4 km depth, emphasizing interesting geological structures.

Such results would help any drilling program in the island (e.g. for geothermal purposes), lead to more successful drilling programs, and serve as well-constrained geologic input to improve the accuracy of future numerical (e.g. reservoir) models.

How to cite: Samperi, L., Berrino, G., and Greco, F.: Subsurface 3D modeling of Pantelleria island (Italy) using gravity data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13204, https://doi.org/10.5194/egusphere-egu24-13204, 2024.

Data-driven methods based on deep learning have been applied to magnetic inversion and achieved excellent results. However, the existing neural network structures used for inversion are relatively complex, resulting in increased computational costs. Different from the inversion structure of existing encoder-decoder structures, this study designed a streamlined neural network inversion architecture based on the characteristics of magnetic anomaly forward modeling. The network structure only contains a decoder that maps magnetic anomaly data to a three-dimensional magnetic susceptibility model, which can save computational costs. First, the single-channel input data is transformed into multi-channel data through a transformation, then it is transformed into the dimensions of the magnetic susceptibility model through a four-layer decoder, and then the multi-channel data is transformed into a single channel through transformation, and finally the output is 3D magnetic susceptibility model. The transformation coefficients are trained by neural network. The neural network structure designed by this method is interpretable. It can reduce the parameters that need to be trained, reduce training time, and achieve high accuracy. It was verified through simulated and measured magnetic anomaly data, and high-precision inversion results were obtained. This idea can also be generalized to the inversion of other data.

How to cite: Shi, X., Geng, H., and Liu, S.: A Streamlined Neural Network Architecture for Magnetic Data Inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8633, https://doi.org/10.5194/egusphere-egu24-8633, 2024.

Here we assessed surface gravity monitoring as tool for detecting the CO₂ plume in deep saline aquifers during the injection and post-injection phases. We used the available benchmark model of the Johansen reservoir to conduct the simulation of CO₂ storage at about 3 km of depth for 70 years and using different injection rates. We calculated the gravity response at surface from the estimated models of reservoir density and saturation at different time intervals. The forward calculation is achieved by assuming a tetrahedral mesh discretization, such as to ensure an accurate and detailed reconstruction of the complex reservoir.

We proposed a new approach for monitoring the mass stored into the reservoir based on the DEXP method, which allows an effective reduction of interference effects from nearby sources and provide accurate results even when the anomaly is incompletely defined, due to a not proper areal coverage of the survey.

This study clearly shows that the appropriate choice of the injection rate strongly impacts on the ability to recover useful gravity signal at the surface, beyond the measurement error threshold. We also provide an in-depth analysis of the effect of noise on the mass change estimates.

Our approach could be a valid tool for conducting real time monitoring of the CO₂ as it could accurately determine the effective mass stored in the reservoir. This is particularly important as it does not require information about the source and could make surface gravity surveying as an independent monitoring strategy.

How to cite: Milano, M. and Fedi, M.: A new approach of monitoring CO2 storage in deep saline aquifers from time-lapse gravity data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18708, https://doi.org/10.5194/egusphere-egu24-18708, 2024.

Serpentinization of ultramafic rocks is a key process in forming natural hydrogen. In deep settings, such as subduction zones, this process can be kinetically favored by high P-T conditions making the study of mantle rocks from these settings a compelling target for high-pressure sources of energy. Serpentinization of peridotites can lead to the formation of magnetite and it is commonly associated with a decrease in density and an increase in magnetization of the protolith rock. Gravity and magnetic methods can therefore be used to map and quantify the extent and degree of serpentinization. Here, we used a comprehensive dataset consisting of ground and Unmanned Aerial Vehicle (UAV) magnetic data, gravity data, and an extensive petrophysical data collection to explore the natural hydrogen potential in exhumed mantle rocks from the Monte Maggiore (MM) massif, in Corsica. The MM massif consists of a ∼4 km² peridotite body, intruded by mafic pods and gabbroic dykes and surrounded by blueschist-facies continental units. It represents sub-continental mantle that underwent tectonic and magmatic evolution during the rifting stage of the Jurassic Ligurian Tethys oceanic basin and successive Alpine subduction to blueschist-facies conditions. On-going geochronological and geochemical investigations suggest that serpentinization occurred primarily in subduction making this area a suitable case study to investigate the formation of high-pressure sources of energy in such settings. We analyzed densities and magnetic properties of rocks from more than 100 sites across the massif and we used these data to identify domains exhibiting different degree of serpentinization and to model the current 3D structure of the massif using both forward and inverse modeling approaches. We estimated a minimum volume of the MM massif of 1.2 km³ and a vertical extent to a depth of 428 m below sea level. We used the modeled volumes and the amount of magnetite within each domain as a proxy for a conservative estimation of natural H₂ production.

How to cite: Pastore, Z., Vitale Brovarone, A., Gattacceca, J., Church, N., Ressico, F., Peverelli, V., Quesnel, Y., Uehara, M., and Kuzina, D.: Using potential field data to investigate high-pressure sources of energy in deeply serpentinized mantle rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18236, https://doi.org/10.5194/egusphere-egu24-18236, 2024.

The current effort to move to more renewable energy sources and away from a petroleum based energy economy, ‘Net Zero’, places a renewed need for improving identification and characterization of mineral deposits in order to provide the materials required. Recent work, has demonstrated the benefit of larger aperture investigations of mineral systems for both determining the processes responsible for their emplacement as well as identifying indicative geophysical signatures associated with metal endowment. The central Norwegian Caledonides historically represent a zone of large mineral endowment, though; the large-scale structural history and process that formed the mineralization remain enigmatic. Formation and concentration of metals into economic mineral deposits requires a combination of processes operating at different scales. With the near surface mineral deposit being a small component of the larger mineral system which encompasses deep fluid sources and metals, an energy source for driving circulation pathways for the migration of enriched fluids, a depositional mechanism responsible for the formation of the deposit and a fluid outflow. The Norwegian mineral deposits lie within the allochthonous nappes, detached from the original Precambrian Svecokarelian and Sveconorwegian basement and having undergone tens to hundreds of km of lateral transport. Regional scale geophysical modelling of petrophysical properties has the ability to characterize and identify the structure and process occurring throughout the entire mineral system  and determine indicative structures at mid-lower crustal depths indicative of economically viable near surface regions of metal endowment (i.e. the near surface mineral deposit). To determine the processes associated with formation of the Norwegian Caledonides and its associated mineral deposits a dense network of ~300 broadband magnetotelluric soundings covering the period range 10^-3-10³s have been collected over two field campaigns in 2022 and 2023 in the Trondelag area of central Norway. Phase tensor analysis indicates that the data set is 3D at all scales – we have modelled the MT data using a 3D approach (GoFEM) capable of incorporating the rugged topography of the survey area. Preliminary modeling results reveal lithospheric-scale structural controls associated with known near surface mineral deposits and processes related to the lateral transport from the underlying lower crustal source regions. As such, regional geophysical surveys offer both an economic and environmentally friendly approach to large-scale exploration efforts through identification of regional scale structural controls that are indicative of metal endowment.

How to cite: Kovacikova, S., Hill, G., Gradmann, S., Klanica, R., Karcioglu, G., Vozár, J., Kamm, J., Mishra, P., Smirnov, M., and Rydman, O.: Image of the crust and upper mantle tectonic structure and associated mineral systems of the central Norwegian Caledonides from 3D inverse geoelectrical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8386, https://doi.org/10.5194/egusphere-egu24-8386, 2024.

We used potential field data to help unravel the geological characteristics of the West Antarctic rift system, one of the largest and least known rift systems on our planet. A comprehensive understanding of this region is lacking, as it is covered by the West Antarctic Ice Sheet (WAIS), which reaches thicknesses of over 3 km. Aeromagnetic and aerogravity datasets collected by the British Antarctic Survey (Ferraccioli et al., 2007) were analyzed via a multiscale analysis (Fedi et al., 2015) useful for identifying the main structural lineaments, i.e., contacts, dykes, sills, volcanic bodies and intrusions in the Pine Island Glacier catchment of WAIS. Our results reveal that several regions are characterized by contact-type sources associated to fault systems bordering major magma-rich rift basins, like the Pine Island Rift, Byrd Subglacial Basin, and Bentley Subglacial Trench, as well as those associated with Pine Island glacier tributaries, which lie at high angle wrt to the glacier trunk and rift basins. Furthermore, we identified magmatic sources near or off-rift zones, such as the edges of the Bentley Subglacial Basin, which allow a better understanding of the sub-ice depth of the magmatic sources. In addition, our results provide new information about the main magmatism trends and their average depths. We thus showcase that potential field anomalies allow a better comprehension of the West Antarctic Rift System regional geology, tectonic architecture and magmatic patterns. This research opens interesting scenarios about the extent and position of magmatic sources and on how they contribute towards shaping the sub-ice topography within this sector of the rift system, which in turn is a primary control on ice sheet flow in this highly dynamic and potentially unstable sector of WAIS. In conclusion, potential field analysis with a multiscale approach emerges as a pivotal tool and provides valuable insights into continental rifting processes, especially in inaccessible areas such as West Antarctica, where there are only very few geological outcrops.

How to cite: Ferrara, G., Ferraccioli, F., and Fedi, M.: Potential fields characterization of inaccessible areas: multiscale analysis of the West Antarctic Rift System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21317, https://doi.org/10.5194/egusphere-egu24-21317, 2024.

According to previous reconstructions, the South Atlantic Ocean is the biggest gap of
Gondwana, with important crustal limits that controls convergent and divergent tectonic
events since the Paleoproterozoic. In the SE Brazilian continental margin, a Cambrian NE-SW
suture zone is marked by an expressive magnetic anomaly onshore that extends offshore to
the proximal Santos basin (Rio de Janeiro). This suture separates two contrasting geological
terranes: a Neoproterozoic magmatic domain (Oriental Terrane), to the west, and a
Paleoproterozoic gneissic terrane, to the east (Cabo Frio Tectonic Domain). The focus is to
determine how this suture extends offshore, hence determining the nature of the basement
that constitutes the continental margin, and how it continues in depth, determining the
orientation of the Ediacaran paleo subduction zone. We made a geological and geophysical
integration aiming to characterize the magnetic pattern of terranes and structures in order to
determinate the geometry and dip direction of the suture in depth. The methodology included
the generation and interpretation of aeromagnetic images combined with geological mapping.
Also, two magnetic sections were made on field along the suture zone and modeled on GMSYS
adopting magnetic susceptibility values obtained both on field and laboratory. The studied
area comprises mainly two geological units separated by a thrust fault (suture zone): dioritic to
granitic Paleoproterozoic rocks with metabasite layers (Região dos Lagos Complex - RLC) and
Ediacaran aluminous paragneisses with calcsilicate layers (Palmital Succession). Based on the
amplitude (intensity), geometry, magnetic signal’s texture and lineament pattern, in map view,
two domains were defined: A1 and A2. The A1 is correlated with the Paleoproterozoic
gneisses, with high amplitude, long wavelength (55 km) with numerous magnetic rectilinear
and curvilinear lineaments. Amplitude ranges between -100 and 452 nT, mostly higher than
150 nT. A2 coincides with the Palmital paragneisses, defined by a low frequency, long
wavelength (55 km) magnetic domain, with amplitudes <0 nT, resulting in a lateral contrast of
more than 500 nT with A1, where the magnetic gradient decreases to NW. Magnetic
lineaments display a preferential NE-SW direction, but in A1 a deep NW-SE fabric occurs, that
might be related with the Paleoproterozoic tectonic fabric. The suture is represented by a high
positive curvilinear lineament, extending offshore, crossing the coastline to SW before
inflecting to the east. Modeling and geological/magnetic maps correlation suggest that the
suture dips to NW. 

How to cite: de Andrade Silva, R. L., da Silva Schmitt, R., Santos Gomes Stanton, N., and Gonçalves Martins, G.: Mapping a Gondwana suture zone integrating magnetic methods and geology at the SE Brazilian continental margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21105, https://doi.org/10.5194/egusphere-egu24-21105, 2024.

Within the Iberian Peninsula and specifically in the Iberian Massif (the westernmost outcrop of the Variscan orogen in Europe), several aeromagnetic anomalies stand out, and many of them are related to late-Variscan gneiss domes. However, some of them are not fully understood because: 1) they are not clearly linked to extensional structures and/or gneiss domes, 2) they are not related with the outcropping rocks, and/or 3) the aeromagnetic map does not provide enough resolution to relate them with the local geology. For example, the Salamanca Magnetic Anomaly (SAMA), in the central-western part of Spain, is a conspicuous reverse polarity magnetic anomaly that features a maximum amplitude of 56.1 nT. However, it does not show any relationship with the magnetic properties of outcropping rocks. In this regard, preliminary studies show that the outcropping Ordovician Slates present randomly reverse polarity Natural Remanent Magnetization which is compatible with that of the SAMA but with very low intensity. Therefore, we have undertaken a large magnetic survey of this anomaly and its continuation to the south. Gravity has also been measured in an effort to constrain the source of the SAMA. The study area, which extends to the south of the city of Salamanca is affected by the Alba-Villoria NE-SW oriented Alpine fault that puts into contact Neoproterozoic and Paleozoic rocks of the Iberian Massif with Cenozoic sedimentary rocks. In addition, the Variscan Salamanca Detachment Zone, a late-Variscan extensional structure allowed deep rocks and crustal melt products to reach shallow crustal levels, probably easing Sn-W mineralization in the area. Our new Bouguer and magnetic anomaly data depict the Alba-Villoria Fault and show a straightforward correlation between gravity and magnetic maxima. Although the magnetic maxima could be the potential field response of dense and magnetic slates common in the area, the ones measured do not present high magnetic susceptibility. Accordingly, this new data might indicate that late-Variscan extension triggered the intrusion of dense and magnetic basic rocks in a process that could have contributed to Sn-W mineralization.

Acknowledgements: We thank the funding provided by the Junta de Castilla y León and Fondo Europeo de Desarrollo Regional (SA084P20), the Fundación Memoria de D. Samuel Solórzano Barruso grant (FS3-2021), Grant PID2020-117332GB-C21 (MCIN/AEI/10.13039/501100011033) and TED2021-130440B-I00 (MCIN/AEI/10.13039/501100011033) and EU NextGenerationEU/PRTR. IDF received support from the Ayuda para la recualificación de sistema universitario español 2021-2023 and MRM from the Programa Margarita Sala, Ministerio de Universidades and UCM (CT18/22).

How to cite: DeFelipe, I., Santamaría Barragán, A., Pérez-Cáceres, I., Ayarza, P., Palomeras, I., Yenes, M., Gómez Barreiro, J., Prieto, R., Rivero-Montero, M., and Sánchez-Sánchez, Y.: High-resolution magnetic and gravimetric map of the South of Salamanca (Spain): tectonic insights and implications on Sn-W mineralization, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5563, https://doi.org/10.5194/egusphere-egu24-5563, 2024.

Delineation of Subsurface Tectonic Structures Using Gravity, Magnetic and Geological Data in the Sarir-Hameimat Arm of the Sirt Basin, NE Libya

By

Mohamed Saleem¹ and Hana Ellafi²

1 &2 Petroleum Research Center

ABSTRACT

The study area is located in the eastern part of the Sirt Basin, in the Sarir-Hameimat arm of the basin, south of Amal High. The area covers the northern part of the Hamemat Trough and the Rakb High. All of these tectonic elements are part of the major and common tectonics that were created when the old Sirt Arch collapsed, and most of them are trending NW-SE. This study has been conducted to investigate the subsurface structures and the sedimentology characterization of the area and attempt to define its development tectonically and stratigraphically.

About 7600 land gravity measurements, 22500 gridded magnetic data, and petrographic core data from some wells were used to investigate the subsurface structural features both vertically and laterally. A third-order separation of the regional trends from the original Bouguer gravity data has been chosen. The residual gravity map reveals a significant number of high anomalies distributed in the area, separated by a group of thick sediment centers. The reduction to the pole magnetic map also shows nearly the same major trends and anomalies in the area. Applying the further interpretation filters reveals that these high anomalies are sourced from different depth levels; some are deep-rooted, and others are intruded igneous bodies within the sediment layers. The petrographic sedimentology study for some wells in the area confirmed the presence of these igneous bodies and defined their composition as most likely to be gabbro hosted by marine shale layers. Depth investigation of these anomalies by the average depth spectrum shows that the average basement depth is about 7.7 km, while the top of the intrusions is about 2.65 km, and some near-surface magnetic sources are about 1.86 km. The depth values of the magnetic anomalies and their location were estimated specifically using the 3D Euler deconvolution technique. The obtained results suggest that the maximum depth of the sources is about 4938m.

The total horizontal gradient of the magnetic data shows that the trends are mostly extending NW-SE, others are NE-SW, and a third group has an N-S extension. This variety in trend direction shows that the area experienced different tectonic regimes throughout its geological history.

How to cite: Saleem, M. and Ellafi, H. and the Mohamed Saleem: Delineation of Subsurface Tectonic Structures Using Gravity, Magnetic and Geological Data, in the Sarir-Hameimat Arm of the Sirt Basin, NE Libya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2060, https://doi.org/10.5194/egusphere-egu24-2060, 2024.

Similar to the feature in the U.S. East Coast, an obvious roughly NE-SW trending high-amplitude magnetic belt (NSCSMA) appears in the northern South China Sea (SCS) continental margin, which extends from southwest Taiwan to the area about 114.5°E and 20°N. The likely cause of this magnetic high is important and interesting but still controversial. This study uses wavelet spectrum analysis, 2-D magnetic modeling, and compact inversion to constrain its causative sources. Our analysis results show the evidence indicating that the geometry and depth of the causative magnetic sources were varied along the strike of the NSCSMA (~15 km in the east and ~25 km in the west). Based on our findings and previous studies, we proposed that the major causative source of the NSCSMA could be the serpentinized upper mantle material.

How to cite: Doo, W.-B., Huang, Y.-S., and Wang, H.-F.: Origins of the high-amplitude magnetic anomaly zone in the northern South China Sea continental margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2767, https://doi.org/10.5194/egusphere-egu24-2767, 2024.

In November 2023, the ESA Swarm constellation mission celebrated 10 years in orbit, offering one of the best-ever surveys of the geomagnetic field and the topside ionosphere. Swarm provides an ideal platform for observing ultra-low frequency (ULF) waves and thus offers an excellent opportunity for space weather studies. For this purpose, a specialized time-frequency analysis (TFA) toolbox has been developed for deriving Pc1 (0.2-5 Hz) and Pc3 (20-100 MHz) wave indices, thus making it a useful tool for the study of magnetic storms. The TFA toolbox is also capable to identify in Swarm time series another category of natural-source electromagnetic signals, i.e., the post-sunset Equatorial Spread-F (ESF) events or plasma bubbles. There have been several studies suggesting that ULF pulsations may be associated with earthquakes. Previous studies refer mainly to the detection of these signals in ground-based magnetometer measurements. Besides, we note only a handful of studies that have been attempted to correlate ULF pulsations with seismic activity, using space-borne magnetometer measurements provided by Low Earth Orbit (LEO) satellites (e.g., CHAMP, DEMETER). Therefore, in this study we focus on the ULF pulsation and ESF activity observed by Swarm satellites during a time interval centered around the occurrence of the August 2016 Central Italy earthquake. Swarm has offered a variety of interesting observations around the time of this earthquake that could be associated with the occurrence of this extreme geophysical event.

How to cite: Balasis, G., De Santis, A., Cianchini, G., Papadimitriou, C., Giannakis, O., and Potirakis, S. M.: Swarm observations of ULF wave activity and plasma instability activity around extreme geophysical events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13361, https://doi.org/10.5194/egusphere-egu24-13361, 2024.