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Large‐scale impact events are some of the most catastrophic and instantaneous geological processes in nature, and leave in their wake conspicuous geological structures with characteristic magnetic anomalies. Despite magnetic anomalies in craters being well‐documented, their relationship with the magnetic mineral composition of the target and impactites is not always straightforward. Furthermore, the influence of impact shock and post‐impact events in the magnetism of natural craters remains elusive. In the Ries crater, Germany, the negative magnetic anomalies are attributed to a reverse polarity remanent magnetization in the impact‐melt bearing lithologies. We report new chemical, rock‐, and mineral‐magnetic data from the shocked basement and impactites, from surface samples, NR73 and SUBO‐18 boreholes, and explore how temperature and hydrothermalism may influence the magnetic mineralogy in the crater. We identified shocked, pure magnetite in the basement, and low‐cation substituted magnetite in the impactites as the main magnetic carriers. The shocked basement is demagnetized but remains largely unaltered by post‐impact hydrothermalism, while the impactites show weak magnetization and are extensively altered by neutral‐to‐reducing post‐impact hydrothermalism. We suggest that the magnetic mineralogy of the demagnetized uplifted basement may contribute significantly to the magnetic anomaly variation, in line with recent findings from the Chicxulub peak‐ring. [ABSTRACT FROM AUTHOR]

The total magnetization of an underground magnetic source is the vector sum of the induced magnetization and the natural remanent magnetization. The direction of the total magnetization serves as important a priori information in the inversion and processing of magnetic data. We demonstrated that the total gradient of the magnetic potential with vertical magnetization constitutes the envelope of the vertical component of the magnetic field for all directions of the Earth's field and source magnetization. The total gradient of the magnetic potential with vertical magnetization and the reduction‐to‐the‐pole field simultaneously tend to achieve maximum symmetry near the correct total magnetization direction. As a result, the total magnetization direction can be estimated by computing the correlations between the reduction‐to‐the‐pole and the total gradient of the magnetic potential with vertical magnetization. The proposed method yields accurate magnetization directions in synthetic model examples. The total gradient of the magnetic potential with vertical magnetization is less susceptible to data noise than transforms which are derived from the high‐order magnetic field derivatives or tensors. The estimation results are slightly affected by changes in the source magnetization direction. In a field example in the Weilasito region (North China), the reduction‐to‐the‐pole fields calculated using the estimated magnetization directions are well centred over the source. The proposed method obtained a more focused magnetization direction than that of a three‐dimensional magnetization vector inversion. The total gradient of the magnetic potential with vertical magnetization therefore provides a novel and accurate approach to determine the total magnetization direction from the total field anomaly in a variety of situations. [ABSTRACT FROM AUTHOR]

Inversion of magnetic basement interfaces in basins is essential for interpreting potential field data and studying geothermal resource distribution, as well as basin formation and evolution. This paper introduces a novel method for inverting magnetic basement interfaces using a random forest regression (RFR) algorithm that combines potential field processing and machine learning techniques. The method creates magnetic base interface models and corresponding magnetic anomaly data through the random midpoint displacement method and magnetic interface finite element forward simulation. These anomalies are then processed using techniques such as directional transformations, analytical continuation, spatial derivatives, and fractional transformations. Feature attributes are extracted, and Gini importance is utilized to measure the contributions of feature factors, identify effective features, and enhance algorithm efficiency. The validity and practicality of the method are demonstrated through the analysis of both idealized and noisy models. The proposed machine learning‐based approach is more intelligent, efficient, and accurately represents the relief of magnetic base interfaces. When applied to magnetic survey data in the Datong Basin, it produced a reliable basin base model that aligns with known structural information, paving the way for further research in magnetic interface inversion. Key Points: A machine learning method based on random forest regression algorithm is used to recover the relief of the magnetic basement interface by using high‐precision magnetic dataApplying potential field processing and transformation to feature extraction for machine learningThe proposed technique intelligently and efficiently restores the 3D relief of the magnetic basement interface, and it has been successfully implemented in the Datong Basin's Tianzhen‐Yanggao sag [ABSTRACT FROM AUTHOR]

The Wayand‐Nilambur granulite terrain in Kerala (India) is well‐known for vein‐type gold mineralization within the quartz veins. Based on the previous geological, petro‐physical and geophysical characteristics of Wayand‐Nilambur gold deposit, the integrated geophysical survey was carried out to delineate the favourable prospecting zones. In the present study, detailed ground geophysical surveys, that is, magnetic, electrical resistivity/chargeability surveys were carried out in an area of 2 km2 in Kattikallu and Kalkulam blocks to delineate the ore deposits in terms of depths and extensions through the structural shear zone, locate the anomalous sources and the geometry of the Au‐rich sulphide zone and its depth continuity in the subsurface. These surveys brought out prominent resistivity and chargeability zones over known magnetite‐quartz veins that are associated with low‐grade sulphide bands at the central part of the Kattikallu block. The prominent potential zone is characterized by strong bipolar magnetic anomalies over the quartz veins. Based on the 2D inversion of resistivity data, the resistivity low zone of order 80–600 Ω m and chargeability of 21–25 mV/V are observed at a depth range of 5–20 m. In Kalkulam block, the magnetic survey has also brought out high intensity anomaly zones over quartz veins, the same quartz veins are mapped by high chargeability of 10–35 mV/V and low resistivity of 185–400 Ω m. The dipole‐dipole configuration produces two parameters, that is, resistivity and chargeability, these methods distinguish the anomalies along the two selected profiles in the study area. An attempt was made for combining the resistivity and chargeability values to identify the anomalous zone boundaries. The results of inversion indicated that the conductive bodies are located at the subsurface, with depths ranging from 5 to 25 m. Based on this integrated geophysical study, we suggested two borehole sites for further geo‐scientific studies in view of mineralization. [ABSTRACT FROM AUTHOR]

Fault structure reconstruction is an important aspect of magnetic prospecting as it contributes to understanding tectonic history, hazard assessment, and infrastructure planning. Metaheuristics have proven useful in estimating fault structure parameters from geophysical anomalies. Recently, a modified version of the Backtracking Search Optimization Algorithm (BSA), named mBSA, has been proposed that combines mutation steps of BSA and Differential Evolution (DE) algorithms to achieve a better balance between exploration and exploitation. Here, we present imBSA as an efficient approach that builds on the improvements of mBSA. It uses an adaptive amplitude control factor in the mutation step derived from a normally distributed random number obtained via an exponential function. The performances of these approaches were tested on some widely used benchmark functions such as Rosenbrock, Rastrigin, Griewank, and Himmelblau. Synthetic magnetic fault anomalies were evaluated with and without noise, as well as three real anomalies from the Dehri (India), Perth Basin, and Lachlan Fold Belt (Australia). Prior to the optimizations, the solvability of the model parameters was examined using some error topography images. The obtained solutions in the synthetic cases were evaluated using principal component analysis. In addition, a novel visualization option for high‐dimensional optimization problems was introduced. The experiments showed that imBSA has a faster convergence rate and better optimization statistics compared to BSA and mBSA. Therefore, it is believed to be an efficient and good alternative tool to widely used metaheuristics such as Particle Swarm Optimization and DE in explaining geophysical anomalies and optimization problems in other geoscientific disciplines. Key Points: Magnetic anomalies of fault structures are interpreted by an improved Backtracking Search Optimization AlgorithmThe efficiency of the proposed algorithm is validated using some benchmarks, synthetic and real magnetic anomaliesThe proposed algorithm has a faster convergence rate to the solutions than its basic and modified versions [ABSTRACT FROM AUTHOR]

Detachment faults at slow‐ and ultraslow‐spreading mid‐ocean ridges are essential for lithosphere‐hydrosphere interactions. However, their coupling with subseafloor hydrothermal circulation is poorly understood. Here, we investigated shallow hydrothermal fluid circulations in the active Dragon Horn detachment fault system of the Southwest Indian Ridge using combined near‐bottom magnetic anomaly data and rock magnetic analyses. We observed enhanced magnetic anomalies related to the high magnetization of basaltic country rocks and highly serpentinized (>80%) peridotite, whereas the hydrothermally altered basalts and sulfide deposits had weak magnetization and reduced magnetic anomalies. Therefore, the low‐magnetization zone was interpreted as a proxy for the hydrothermal fluid channel. The spatial distribution of the low‐magnetization zone revealed that the inactive Suye field expanded more than 500 m in diameter horizontally and ∼100 m vertically, and the active Longqi hydrothermal field had a >1 km fluid channel, both centered around the detachment fault fracture zone. Our results establish a robust link between detachment faulting and shallow hydrothermal circulation in which the detachment fault system provides critical fluid paths. Therefore, detachment tectonics are important elements for evolving seafloor hydrothermal fields along the Southwest Indian Ridge and possibly other slow‐ and ultraslow‐spreading mid‐ocean ridges globally. Plain Language Summary: The detachment faults of slow‐ and ultraslow‐spreading mid‐ocean ridges are geological structures motivated by seafloor spreading. Intermitted movements of detachment faults exhume deep oceanic crust or mantle rocks and provide pathways for seafloor hydrothermal systems. The magnetic properties of rocks in seafloor detachment fault systems are sensitive to hydrothermal fluids and can be used to study fluid circulation within seafloor detachment fault systems. Using magnetic methods, we found that magnetic minerals in fresh basalt and highly serpentinized peridotite created positive magnetic anomalies, whereas the absence of magnetic minerals in hydrothermally altered basalts and sulfides decreased the magnetic anomalies. As represented by the low‐magnetization zones, the shallow hydrothermal fluid channels sit on the detachment fault, highlighting the close relationship between detachment tectonics and the evolution of seafloor hydrothermal systems. We conclude that the detachment fault system primarily controls the formation of black‐smoker chimneys along the magma‐poor mid‐ocean ridges. Key Points: Altered basalt and sulfide deposits attenuated the magnetic anomaly of the normal‐polarity zone in the Dragon Horn areaSerpentinized peridotite (>80%) produced significant positive magnetic anomalies in the Dragon Horn areaDetachment faulting controls the formation of fluid channels for hydrothermal circulation [ABSTRACT FROM AUTHOR]

The 2018 crisis of Kīlauea volcano stands as a major event in its evolution with a large down‐rift effusive eruption that drained a shallow magma reservoir at the summit. The characterization of such active magmatic systems and associated hazardous events remains a necessity and a challenge. The summit area is hydrothermally active and strongly altered as indicated by geological mapping. A unique data set of geophysical measurements was collected around Halemaʻumaʻu crater before its collapse. Magnetic data are interpreted here in combination with geological information, temperature anomalies at the surface, self‐potential measurements, and a model of electrical conductivity. 3D forward modeling shows that the main magnetic dipole‐like anomaly observed around the crater is not only caused by the crater topography but suggests the presence of an important volume of weakly magnetic material beneath the crater, which may be caused by higher temperature and/or hydrothermal alteration. 3D inversion of the data allows us to explore the first order geometry of the magnetic structures. We complement this inversion with 2D forward modeling in order to refine the geometry of major structures. This study shows the presence of major geological structures in the 2018 collapsed area that may have been associated with mechanical weaknesses and could have played a role in the geometry of the collapse. Therefore, mapping magnetic anomalies and monitoring their temporal evolution are of great interest for constraining the nature and mechanical properties of the underlying formations and their temporal evolution in order to help predict future behavior. Plain Language Summary: Kīlauea ranks among the world's most active volcanoes alternating between effusive and explosive events, implying for example, large caldera collapses. The 2018 eruption is the most recent major volcano‐tectonic event that has significantly affected the Kīlauea summit. Assessment of associated hazards is a necessity and a challenge and requires the imaging of hidden weakness zones within the volcano and the monitoring of their evolution through time. We use here a survey of magnetic measurements collected in 2015 at the Kīlauea summit in order to image the subsurface distribution of rock magnetization. These data allow us to demonstrate the presence below the Halemaʻumaʻu crater of a large volume of material characterized by weak magnetization and to delineate its geometry. This weak magnetization can be caused by high subsurface temperatures and/or rock modifications caused by interaction with hot fluid circulations. We also identify major structures that may have been weakness zones and could have played an important role in the geometry of 2018 collapse. This study suggests that the repetition of magnetic surveys over volcanoes in order to monitor the temporal evolution of their subsurface magnetization could help predict the future evolution of the volcanic system. Key Points: We present a new ground magnetic data set collected at the Kīlauea summit around the Halemaʻumaʻu crater before its collapse in 20182D and 3D modeling of these data indicate the presence of weakly‐magnetized material below the crater and along a major fissure zoneThis data set shows the presence of major structures that may have been pathways to fluids and may have played a role in the 2018 collapse [ABSTRACT FROM AUTHOR]

Changes in Earth's magnetic field during the Cretaceous Normal Superchron (CNS) spanning ∼121 Ma to ∼84 Ma hold important clues about the geodynamo evolution. Canonical models predict a persistently strong geomagnetic field with low variability during CNS, which, however, has not been observed in the available absolute paleointensity data and seafloor marine magnetic anomaly (MMA) records. The lack of relative paleointensity (RPI) data across CNS further impedes tests of model predictions. Here, we present a ∼9‐Myr (∼94–∼85 Ma) RPI record from a Turonian to Santonian hemipelagic succession from IODP Site U1512 offshore southern Australia. Detailed paleomagnetic and rock magnetic analyses demonstrate that the ratio of natural remanent magnetization (NRM) demagnetized at 20 mT over magnetic susceptibility (MS), that is, NRM20mT/MS, as a reliable proxy for the RPI of the Upper Cretaceous succession. The new RPI record shows marked changes in both intensity and variability at ∼90.8 Ma. Also, the 6 Myr‐long (∼94–∼88 Ma), near‐continuous, ∼1.2 kyr‐resolution RPI record exhibits a strong positive correlation between field intensity and variability. Assuming this correlation holds for the entire CNS, an extrapolated RPI curve for the entire CNS is obtained by integrating the positive correlation with field variability estimates from the MMA data. The extrapolated RPI curve shows a strong and highly variable field in the middle CNS but a weak and stable field at its beginning and ending. These features imply a much more dynamic geodynamo than previously thought, and provide crucial benchmarks for unraveling the geodynamo evolution during CNS. Plain Language Summary: Cretaceous Normal Superchron (CNS, ∼121 to ∼84 million years ago) marks a nearly 40 million years interval of almost constant normal geomagnetic polarity. Changes in Earth's magnetic field during CNS hold important clues about the evolution of the geodynamo, by which the geomagnetic field was generated. However, whether the geomagnetic field was persistently strong and stable during CNS has been controversial based on estimates from snapshot recordings of igneous rocks and marine magnetic anomaly data. Here, we report a high‐resolution near continuous relative paleointensity (RPI) record of the ∼88–94 million years old interval from a hemipelagic sedimentary succession at IODP Site U1512. The new RPI record documents salient changes in both intensity and variability of the geomagnetic field at ∼90.8 million years ago and a positive correlation between these two parameters toward the ending of CNS. These features imply that the geomagnetic field was strong and highly variable in the middle CNS, but weak and stable at its beginning and ending. These findings indicate much more dynamic geodynamo behavior during the CNS than previously thought, and thus provide important benchmarks for "ground truthing" model simulations to unravel the geodynamo evolution during CNS. Key Points: We report a ∼9 Myr high‐resolution RPI record for the late stage (∼94–∼85 Ma) of CNS from IODP Site U1512 coresThe new RPI record shows a marked change in intensity and variability at ∼90.8 Ma and a positive correlation between these two parametersSalient changes in geomagnetic field's strength and variability imply a much more dynamic geodynamo than previously thought during CNS [ABSTRACT FROM AUTHOR]

Craters on Mars are a window into Mars' past and the time they were emplaced. Because the crust is heated and shocked during impact, craters can demagnetize or magnetize the crust depending on the presence or absence of a dynamo field at the time of impact. This concept has been used to constrain dynamo timing. Here, we investigate magnetic anomalies associated with craters larger than 150 km. We find that most of those craters, independent of age, exhibit demagnetization signatures in the form of a central magnetic low. We demonstrate a statistically significant association between such signatures and craters, and hypothesize that the excavation of strongly magnetic crustal material may be an important contribution to the dominance of demagnetized craters. This finding implies that the simple presence or absence of crater demagnetization signatures is not a reliable indicator for the activity of the Martian dynamo during or after crater formation. Plain Language Summary: Craters on Mars allow studying the time at which they were emplaced and as such they are a window into Mars' past. Because the crust is heated and shocked during impact and thus recrystallization occurs, craters can demagnetize or magnetize the crust depending on the presence or absence of a dynamo field at the time of impact. A classic magnetization signature is expressed by a magnetic high in the crater interior and the youngest of those craters have been used to constrain dynamo timing. Here, we investigate magnetic anomalies associated with all craters larger than 150 km. We find that most of those craters and independent of age exhibit a demagnetization signature, and fewer a magnetization signature. In general, the largest craters show a demagnetization signature. To explain the dominance of demagnetization signatures we hypothesize that the excavation of strongly magnetic crustal material may be an important process. This finding implies that the simple presence or absence of crater magnetization signatures is not a reliable indicator for dynamo activity and magnetic signatures of craters are dependent on multiple parameters such as crustal thickness. Key Points: Craters on Mars dominantly show demagnetization signaturesLarge craters and thin crust promote magnetic lows in the crater interior irrespective of dynamo activityCrustal excavation is likely an important process that promotes demagnetization signatures [ABSTRACT FROM AUTHOR]

The slow spreading Reykjanes Ridge overlies the Iceland hotspot and has undergone well ordered changes in crustal segmentation. Previous studies have attributed these changes to varying mantle plume thermal effects, rendering the lithosphere ductile or brittle. Here we use seafloor spreading magnetic anomalies to show that crustal accretion has been focused throughout its spreading history and to determine the detailed evolution of Reykjanes Ridge segments. By ∼53 Ma, organized spreading had developed on an orthogonally spreading linear axis following continental breakup. After a plate motion change at ∼38 Ma, orthogonally spreading offset ridge segments formed by ridge propagation forming varying length fracture zones. From then to the present, the offset segments diachronously migrated back to the original linear geometry from north to south replacing orthogonal with oblique spreading as the axis became linear again. Fracture zones were not terminated, however, simply by reducing segment offsets even to zero. Their termination involved the axial propagation of buoyant upwelling instabilities across the discontinuities, correspondingly extending V‐shaped crustal ridges southward. This evolution was guided by a persistent linear deep damp mantle melting interval maintained by the episodic propagation of buoyant upwelling instabilities. Our study indicates that at slow spreading ridges, where buoyant upwelling instabilities govern crustal segmentation, spatial gradients in mantle melting properties may direct the behavior of the instabilities. Where ridges overlie regional hotspot gradients in mantle melting, buoyant instabilities may propagate systematically, and plate boundary evolution may follow an organized pattern. Plain Language Summary: As the Reykjanes Ridge overlies the Iceland hotspot, much of its evolution has been proposed to reflect varying mantle plume thermal effects. Here we use seafloor spreading magnetic lineations to study this evolution and better understand controlling mechanisms. We find that typical plate tectonic processes can account for the evolution without resorting to changing mantle plume thermal effects. However, a persistent regional gradient in mantle melting associated with the Iceland hotspot strongly directs the evolution. The ridge originated as a linear axis. It became fragmented by rift propagation following a plate motion change. The offset segments then progressively reassembled their original linear geometry by asymmetric spreading. Axial propagation of buoyant upwelling instabilities terminated fracture zones when segment offsets became small. This evolution was guided by a deep zone of mantle melting that remained linear, maintained by axially propagating buoyant instabilities that also form V‐shaped crustal ridge on the ridge flanks. Our study indicates that at slow spreading ridges where buoyant mantle upwellings govern crustal segmentation, factors that influence mantle melting can direct the motion of the instabilities. Where hotspots form pronounced along‐axis melting gradients, buoyant upwelling centers and crustal segmentation can follow an organized evolution. Key Points: Overlying the Iceland hotspot, the Reykjanes Ridge underwent a remarkably organized plate boundary evolutionThe linear ridge became fragmented following a plate motion change then systematically reassembled its original linear configurationThe Iceland hotspot melting gradient causes buoyant mantle upwelling cells to propagate, reestablishing the original linear axis [ABSTRACT FROM AUTHOR]

The South Atlantic Anomaly (SAA) refers to a region where the strength of the magnetic field is notably weaker compared to a dipole field. While previous studies have primarily focused on its effects on the inner radiation belt, this study investigates its impact on the aurora system. By analyzing 2 years' worth of data obtained by the Fengyun‐3E/ACMag instrument, we discover that magnetic fluctuations within the auroral oval are significantly weaker in the longitude sector corresponding to the SAA, as compared to those outside this area. This characteristic remains permanent and independent of seasons and geomagnetic activities. Additional investigation using Defense Meteorological Satellite Program/Special Sensor Ultraviolet Spectrographic Imager (DMSP/SSUSI) observations reveals a similar phenomenon in the auroral intensity. Therefore, our results demonstrate that the SAA substantially weakens the aurora system, shedding new light on the effects of magnetic anomalies on planetary auroras and magnetosphere‐ionosphere‐thermosphere coupling. Plain Language Summary: The South Atlantic Anomaly (SAA) is a unique location on Earth where the magnetic field is weaker than normal. This region has drawn a lot of attention because its weakened magnetic field brings the inner Van Allen radiation belt unusually close to the Earth's surface, which poses a threat to satellites passing through it. Here, we uncovered another interesting aspect of the SAA: its impact on the aurora system. To investigate this, we first examined 2 years' worth of data from the ACMag instruments on the Fengyun‐3E satellite, which orbits the Earth at an altitude of 836 km in a dawn‐dusk, Sun‐synchronous orbit. Our findings reveal that the magnetic fluctuations within the southern auroral oval are significantly weaker in the region that aligns with the SAA. This weakening effect is consistently present, regardless of the season or the level of geomagnetic activity. To reinforce our results, we also analyzed auroral intensity from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on the Defense Meteorological Satellite Program (DMSP) satellite, and it corroborated the same weakening trend in this data set. In conclusion, our observations demonstrate that the SAA has a substantial impact on weakening the aurora system. This discovery deepens our understanding of how magnetic anomalies can influence planetary auroras. Key Points: The effects of the South Atlantic Anomaly (SAA) on the terrestrial aurora system are examined using multiple instrumentsObservations reveal a substantial weakening of auroral magnetic fluctuations and auroral intensity in the SAA longitude sectorThe results indicate considering magnetic anomalies like the SAA is essential for comprehensively understanding planetary aurora systems [ABSTRACT FROM AUTHOR]

Large impact craters on Earth are associated with prominent magnetic anomalies, residing in magnetite of the shocked target rocks and impactites. Shock experiments on magnetite suggest that up to 90% of magnetic susceptibility is lost at pressures >5 GPa, but can be partially restored by post‐shock thermal annealing. The magnetic property changes are caused by shock induced grain size reduction and fragmentation, as well as domain wall‐pinning at crystal lattice defects. A recent study of granitoids from the peak‐ring of the Chicxulub crater found that annealing may occur naturally, but can also be overprinted by high‐temperature hematite‐to‐magnetite transformation in non‐oxidizing environments. In this study, we isolate the effect of defect annealing and hematite‐to‐magnetite transformation using the evolution of hysteresis, isothermal remanent magnetization components and first order reversal curve (FORC) diagrams at different high‐temperature steps. We used a laboratory‐shocked magnetite‐quartz ore, a non‐shocked naturally oxidized granite, and a naturally shocked and oxidized granite. Our findings suggest that annealing of shock‐induced lattice defects partially restores some pre‐shock magnetic behavior and causes an apparent average bulk‐sample domain state increase. Hematite‐to‐magnetite transformation creates new fine‐grained magnetite that strongly overprints the original signal, and decreases the average bulk‐sample domain state. Where annealing and hematite‐to‐magnetite transformation both occur, the new magnetite masks the annealing‐induced property restoration and apparent domain state modification in the shocked magnetite. As magnetite oxidation is a ubiquitous process in surface rocks, these findings are fundamental to understand hematite‐to‐magnetite transformation as a potential overprint mechanism, and could have broad implications for paleomagnetic interpretations. Plain Language Summary: Magnetite is the dominant magnetic mineral in the Earth's crust and is also found in shocked rocks of impact craters, where it can lose up to 90% of its induced magnetization due to fractures and defects in the crystal lattice. Previous experiments in shocked magnetite ore suggest that thermal treatment can recover some shock‐induced defects, and even restore some lost magnetic properties. Similar changes in magnetic properties have been observed in non‐shocked granites with magnetite and hematite after heating, because in non‐oxidizing environments hematite transforms back to very small magnetite grains at high temperatures. Shocked magnetite from the Chicxulub crater is also oxidized to hematite before the impact, and it is unclear if the heating‐induced change of magnetic properties is due to the recovery of shock defects, or hematite‐to‐magnetite transformation. We investigated magnetite from a laboratory‐shocked magnetite‐quartz ore, a non‐shocked naturally oxidized granite, and the granite from Chicxulub at different temperature steps with high‐resolution magnetic methods, and delineated the effects of physical and chemical alteration. We find that hematite‐to‐magnetite transformation overprints the original signal in a similar way to the annealing of shock‐induced features. This study is fundamental for discriminating shock and chemical alteration on the magnetic behavior of magnetite. Key Points: Shock‐induced lattice defects in magnetite alter magnetic behavior and apparent magnetic domain state; annealing partially restores themHematite in oxidized magnetite transforms back to magnetite with heating. Newly formed magnetite has a SD‐SP grain size rangeUsing high‐resolution FORC analysis, we distinguish between annealing and newly formed magnetite from transformation in heating experiments [ABSTRACT FROM AUTHOR]

Holleford Crater is a deeply buried, 2.35 km diameter late Proterozoic‐early Cambrian (550 ± 50 Ma) simple impact crater located in southeastern Ontario, Canada. Exploration drilling in the 1950–60s indicated a >450 m deep, simple impact structure with an infill stratigraphy of Cambro‐Ordovician clastic and carbonate sediments and a −2.2 mGal gravity anomaly. We conducted new ground‐based geophysical surveys (magnetics, gravity) and potential field modeling to better resolve the buried impact structure depth, subsurface geometry, and postimpact modification. Geophysical surveys reveal a well‐defined ~3 mGal Bouguer gravity low and <20 nT residual magnetic anomaly over the crater basin. The lack of a well‐defined magnetic anomaly is due to the low magnetic contrast between Mesoproterozoic metasedimentary target rocks and Paleozoic infill sediments. The modeled basement surface shows a deeply buried (>400 m), eroded simple impact structure with a rim‐to‐rim diameter (D) of 1.8–2 km, a residual rim height of about 30 m and a true depth (dt) >400 m. The modeled diameter is smaller than the previous estimate (2.35 km) based on the surface outcrop pattern of Paleozoic strata, which overestimates the buried impact structure dimensions. The modeled basement surface identifies a rim breach and a possible fluvial outflow channel in the southeast impact structure rim. The channel is up to 150 m deep and 400 m in width and has morphology similar to outlet channels produced by fluvial rim dissection of terrestrial impact structures and "tadpole craters" on Mars. [ABSTRACT FROM AUTHOR]

Materials exhibiting irreversible phase transitions, leading to changes in their properties, have a potential for novel application in electronic components such as a non‐rewritable high‐security memory. Here, we focused on the two salts, [(9‐triptycylammonium)([18]crown‐6)][Ni(dmit)2] (1) and [(9‐triptycylammonium)([15]crown‐5)][Ni(dmit)2] (2), which featured 2D sheet structures with alternately stacked cation and anion layers. Both salts exhibit similar cation arrangements, however, their anion arrangements differ significantly. The temperature‐dependent magnetic susceptibilities of 1 and 2 were well reproduced by the alternating chain model (JAC1/kB=−306(8), JAC2/kB=−239(3) K) and the Curie‐Weiss model (θ=−3.9(1) K), respectively. 1 experience a reversible phase transition around 40–60 K, causing anomalies in magnetic behavior. Moreover, an irreversible single‐crystal‐to‐single‐crystal phase transition to 1′ undergo at ~381 K, inducing a rearrangement of [Ni(dmit)2]− anions and a resistivity decrease from 6.5×106 to 6.5×102 Ω cm. The susceptibility curve of 1′ was reproduced by a combination of the Curie‐Weiss and dimer models (Jdimer/kB=−407(5), θ=−26.7(5) K). The irreversible transition of 1 is the first example for such supramolecule and [Ni(dmit)2]− system to our knowledge, in opening potential new‐type materials. [ABSTRACT FROM AUTHOR]

Crustal magnetic anomaly maps over oceanic regions are based largely on marine trackline surveys. These surveys, collected from the 1950s to the present, span a wide range of data quality and reliability. We discuss a methodology for constructing grids from these data with associated cell by cell estimates of grid uncertainty. The method is tested with a modern airborne survey for a representative region in the eastern Caribbean. The results are promising, producing an uncertainty estimate that is accurate to one standard deviation for the test area. As magnetic anomaly maps and grids are increasingly applied as constraints for geologic interpretation as well as for alternative navigation (e.g., navigation by magnetic field patterns in the absence of GPS), it is important to quantify the accuracy of these maps. Plain Language Summary: It is challenging to make maps of the variations in the Earth's magnetic field, called crustal magnetic anomalies, caused by the distribution of magnetic minerals in oceanic areas. The reason for this is that the best available data for most marine areas is from ship‐based measurements collected over many decades, from the 1950s to the present. The spatial distribution of these marine survey tracklines is highly variable as is their original data quality and reliability. Previous grids and maps constructed from marine trackline data have not included systematic estimation of the grid/map uncertainty. At best, earlier maps have included generalized statements about the estimated mean uncertainty. In this study, we present a methodology for estimating the crustal magnetic anomaly and the associated uncertainty from marine trackline data. The method is evaluated using a modern airborne survey of a test area in the eastern Caribbean, an area surrounding St. Croix in the US Virgin Islands. Key Points: Marine crustal magnetic anomaly maps are typically constructed from trackline data with variable uncertainties and spatial configurationsThis paper presents a methodology for creating data grids with associated cell by cell uncertainty from marine trackline dataThe method is tested against newly collected modern airborne magnetic data [ABSTRACT FROM AUTHOR]

Geomagnetic anomaly interpretation through inversion procedures often yields useful results in determining the key details of ore masses. However, the problem is complicated due to the known ambiguous phenomena of the inversion process. Thus, details such as location, depth and shape can only be estimated using an efficient algorithm. To this end, we presented here a novel global optimization algorithm called Hunger Games Search (HGS) for the inversion of geomagnetic anomalies caused by ore masses. HGS is a well‐organized metaheuristic inspired by the hunger‐driven instincts and social behavioral decisions of animals. This is the first work in the literature to introduce this optimizer for the inversion of geophysical anomalies. We revealed the model parameter dependencies and the optimum control parameter values of the algorithm by performing some modal analyses and parameter tuning studies, respectively. The capability of HGS was demonstrated on synthetically produced geomagnetic responses and on three real anomalies obtained from some exploration fields in India and the USA. Uncertainty appraisal studies showed the solidity of the outputs of the algorithm. Moreover, some comparative studies with the fine‐tuned standard Particle Swarm Optimization, a commonly used tool for the inversion of geophysical anomalies, indicated that HGS algorithm provides better results in terms of convergence characteristics and solution stabilities in the presented inverse problem. We therefore recommend the use of this metaheuristic in model parameter estimation studies when dealing with this kind of geophysical potential field problems. Plain Language Summary: A new global optimization algorithm, named Hunger Games Search (HGS), is presented for the inversion of geophysical data sets. The efficiency of the algorithm is tested on geomagnetic anomalies originated from different ore masses and synthetic data sets. The applications show that the proposed inversion algorithm produces reliable results and outperforms standard Particle Swarm Optimization, which is the most widely used global optimization algorithm in the inversion of geophysical data sets. We conclude that the HGS algorithm is a powerful inversion tool for geophysical anomalies. Key Points: This is the first study in the literature to apply Hunger Games Search algorithm to geophysical anomaliesPost‐inversion analyses showed the reliability of the solutions obtained in synthetic and field data casesCompared to the standard Particle Swarm Optimizer, proposed algorithm outperformed in the presented inverse problem [ABSTRACT FROM AUTHOR]

Recent observations and geophysical studies at the Vredefort impact structure have indicated that the impact melt dikes in the central uplift of the structure have small depth extents. In this study, we performed magnetic and electrical resistivity tomography (ERT) surveys of the Lesutoskraal granophyre dike (LGD) and trenched to confirm its depth extent. The ERT survey showed that outcrops of the LGD are associated with shallow resistive zones with <3 m depth extent, but such zones do not occur where outcrops are absent. Visual observations in the trench confirmed that the dike has a small depth extent (~0.75 m) at this location. However, the magnetic survey revealed anomalies along the entire strike of the dike, even where no outcrops occur. We suggest that remagnetization of the host rock within a metamorphic contact aureole could explain the presence of magnetic anomalies in the absence of outcrops. Considering the results of the ERT survey, the observations made in the trench, and the surface distribution of outcrops of the LGD, we confirm that this dike has a small depth extent (<3 m) along its entire length and propose that outcrops represent the intersection of the dike terminus with the current erosional surface. [ABSTRACT FROM AUTHOR]

Maar‐diatreme volcanoes are small volcanic structures with a funnel‐shaped crater surrounded by a tephra‐ring. They are usually formed by the explosive phreatomagmatic eruptions when groundwater comes into the contact with magma. We focus on such a structure in the geodynamically active western Eger Rift (Czech Republic) and present results from multidisciplinary geophysical investigation calibrated by drilling in the newly discovered Pleistocene Bažina maar. We evaluated morphological (LiDAR‐based DEM) data and confirmed the existence of a maar‐diatreme structure by combined geophysical methods. In the map view, they revealed circular negative gravity anomaly, funnel‐shape low‐resistivity anomaly, and strong magnetic anomaly. These results allowed for the optimal location of two boreholes in the maar crater, which evinced its contact with country rocks and lithologies of the maar‐diatreme filling. The drilling revealed coherent volcanic rocks and volcaniclastic deposits, moreover, it revealed a presence of a pyroclastic cone with the olivine nephelinite feeding conduit. Further investigations disclosed maar structure and subsequent pyroclastic cone(s) with several generations of eruptions and systematic decrease of water influence on the eruption style. Different eruption styles suggest a unique evolution of two volcanoes, one inside the other. The age of the Bažina maar eruption, estimated from the reverse polarity of the detected magnetic anomaly, implies that the effusion and solidification of the lava during the eruption must be older than 0.78 Ma (Pleistocene). This points to an active volcanism in the western Eger Rift in a span of ∼0.5 Ma, where Bažina represents the oldest (maybe opening) phase. Plain Language Summary: Maars are small volcanoes formed by the explosive eruptions when water comes into the contact with magma. They can form topographic depressions, however, their discovery is not easy and they can be easily missed in the fields. We focused on a newly discovered depression Bažina in the western Eger Rift (Czech Republic), which was supposed to be such a maar. Combination of geophysical surveys and drilling revealed small volcano with a complex structure. Geophysical results proved its magmatic origin and allowed for the optimal location of two exploration boreholes. They evinced the maar contact with the country rocks, coherent volcanic rocks and volcaniclastic deposits with basaltic conduit. Further investigations disclosed several subsequent eruptions within the maar with different eruption styles, from maar‐forming eruption to Surtseyan style eruption and finally to Strombolian style eruption. These different eruption styles suggest the unique evolution of two volcanoes, one inside the other. The schematized animated history of this volcano is accessible at https://www.youtube.com/watch?v=VxhFrM6WR8c. Key Points: We investigated maar‐diatreme structure of the new Pleistocene Bažina maar in the western Eger Rift by combined geophysical and drilling researchGeophysical methods verified the maar origin, lithologies from two boreholes revealed volcanic rocks with basaltic feeding conduitOur multidisciplinary approach disclosed several generations of eruptions leading to a formation of another scoria cone within the maar [ABSTRACT FROM AUTHOR]

Detailed models of crustal structure at volcanic passive margins offer insight into the role of magmatism and the distribution of igneous addition during continental rifting. The Eastern North American Margin (ENAM) is a volcanic passive margin that formed during the breakup of Pangea ∼200 Myr ago. The offshore, margin‐parallel East Coast Magnetic Anomaly (ECMA) is thought to mark the locus of syn‐rift magmatism. Previous widely spaced margin‐perpendicular studies seismically imaged igneous addition as seaward dipping reflectors (SDRs) and high velocity lower crust (HVLC; >7.2 km/s) beneath the ECMA. Along‐strike imaging is necessary to more accurately determine the distribution and volume of igneous addition during continental breakup. We use wide‐angle, marine active‐source seismic data from the 2014–2015 ENAM Community Seismic Experiment to determine crustal structure beneath a ∼370‐km‐long section of the ECMA. P‐wave velocity models based on data from short‐period ocean bottom seismometers reveal a ∼21‐km‐thick crust with laterally variable lower crust velocities ranging from 6.9 to 7.5 km/s. Sections with HVLC (>7.2 km/s) alternate with two ∼30‐km‐wide areas where the average velocities are less than 7.0 km/s. This variable structure indicates that HVLC is discontinuous along the margin, reflecting variable amounts of intrusion along‐strike. Our results suggest that magmatism during rifting was segmented. The HVLC discontinuities roughly align with locations of Mid‐Atlantic Ridge fracture zones, which may suggest that rift segmentation influenced later segmentation of the Mid‐Atlantic Ridge. Plain Language Summary: The East Coast of the United States is a passive margin that formed during continental breakup of Pangea, the most recent supercontinent. Although passive margins are generally not locales of active faulting and magmatism, by investigating their current structure, we gain insight into processes during past rifting. We know that extensive volcanism and magmatic addition to the Earth's crust occurred during the breakup of Pangea, but we do not fully understand how the distribution changes from north to south along the margin. To study these rocks, which are buried 10–20 km beneath the seafloor, we use ocean bottom seismometers to determine the sound speed of rocks beneath the surface, which can tell us about composition and rock type. We found that the thickness and extent of magma‐derived rocks are variable along the margin, with gaps up to 30 km wide. This variability is likely related to processes happening in the continental rift which may have influenced the structure of the Mid‐Atlantic Ridge that formed after rifting ended. Key Points: High velocity lower crust beneath the East Coast Magnetic Anomaly is variable along‐strike and discontinuous in some placesThe lower crust variability reflects variable intrusion into lower continental crust and represents magmatic segmentation during riftingThe high velocity lower crust discontinuities are coincident to Mid‐Atlantic Ridge fracture zones, suggesting a rift‐to‐ridge connection [ABSTRACT FROM AUTHOR]

Valdivia Bank (VB) is a Late Cretaceous oceanic plateau formed by volcanism from the Tristan‐Gough hotspot at the Mid‐Atlantic Ridge (MAR). To better understand its origin and evolution, magnetic data were used to generate a magnetic anomaly grid, which was inverted to determine crustal magnetization. The magnetization model reveals quasi‐linear polarity zones crossing the plateau and following expected MAR paleo‐locations, implying formation by seafloor spreading over ∼4 Myr during the formation of anomalies C34n‐C33r. Paleomagnetism and biostratigraphy data from International Ocean Discovery Program Expedition 391 confirm the magnetic interpretation. Anomaly C33r is split into two negative bands, likely by a westward ridge jump. One of these negative anomalies coincides with deep rift valleys, indicating their age and mechanism of formation. These findings imply that VB originated by seafloor spreading‐type volcanism during a plate reorganization, not from a vertical stack of lava flows as expected for a large volcano. Plain Language Summary: Oceanic plateaus are large, elevated underwater features commonly formed from volcanic material from a hotspot. Valdivia Bank is a Late Cretaceous oceanic plateau in the southeast Atlantic Ocean formed by volcanism from the Tristan‐Gough hotspot near the Mid‐Atlantic Ridge. The origin and evolution of Valdivia Bank is poorly defined, but new magnetic data suggests the edifice originated through ridge‐centered volcanism, with lateral accretion of crust. This is unlike the evolution of a massive volcano, which would be expected to create a vertical stack of lava flows. Magnetic inversion modeling suggests the plateau was formed by seafloor spreading during the formation of anomalies C34n‐C33r, with the plateau becoming younger from east to west, rather than north‐south as predicted by some hotspot models. Results from International Ocean Discovery Program Expedition 391 paleomagnetism and biostratigraphy confirm the anomaly interpretation. Key Points: Valdivia Bank is characterized by quasi‐linear magnetic anomalies that are parallel to the inferred paleo‐Mid‐Atlantic RidgeMagnetic anomalies imply that the plateau becomes younger E‐W consistent with formation via seafloor spreading during anomalies C34n‐C33rRift valleys, division of C33r, and anomaly curvature imply complex ridge tectonics and a ridge jump [ABSTRACT FROM AUTHOR]

The Mt. Melbourne Volcanic Field is a quiescent volcanic complex located in Northern Victoria Land, Antarctica, mostly covered by ice. Its inner structure has remained largely unknown, due to the paucity of outcrops and the lack of detailed multi‐disciplinary investigations. Here we present a novel high‐resolution aeromagnetic dataset, revealing strong long‐wavelength negative anomalies superimposed by short‐wavelength positive ones forming characteristic radial patterns. Automatic lineament detection, through the Hough transform technique applied to the tilt derivative of our magnetic dataset, shows prevailing NW‐SE‐to NNE‐SSW‐trending structural features, which combined with the few structural field observations contribute to define the deformation pattern. Pre‐existing and novel magnetic property measurements, coupled with available geochronological data, are used to constrain a two‐step 3D magnetic inversion. A layer‐structured Oldenburg‐Parker's inversion was utilized to model the deep and long‐wavelength components of the magnetic field, whereas a linear inversion based on a set of shallower prisms was used to model the short‐wavelength components. The final 3D model shows widespread reversely‐polarized volcanics, which are locally intruded and superimposed, respectively by swarms of normally‐polarized dikes and radial lava flows along paleo‐valleys. These results support the onset of volcanic activity in the entire field at least in the Matuyama magnetic epoch, that is, between 2.58 and 0.78 Ma. Plain Language Summary: Airborne high‐resolution magnetic data play a crucial role in the understanding of the geological structure of ice‐buried volcanoes. In fact, an interesting property of magnetic minerals contained in volcanic rocks is that of retaining, after cooling below a certain characteristic temperature (i.e., Curie temperature), a permanent magnetization called remanent. Its direction (polarization) at the South Pole can be normal if rocks are cooled when the Earth's magnetic field presents negative inclination (as the current Brunhes epoch), whereas reverse in the case the Earth's magnetic field shows positive inclination (i.e., the Earth's magnetic field poles swap places). As a consequence, at polar latitudes, positive magnetic anomalies are associated with normally‐polarized rocks and, conversely, negative anomalies with reversely‐polarized rocks. Thanks to this property, in this study we have carried out the first reconstruction of the internal architecture of the Mt. Melbourne Volcanic Field. Our results, constrained by independent geological and geophysical information, suggest the volcanic complex is composed mainly by an older reversely‐polarized unit superimposed and intruded locally by younger normally‐polarized lava flows. Being the periods of magnetic polarity reversal well known, we have been able to estimate the beginning of a widespread volcanic activity before the last Brunhes‐Matuyama polarity reversal. Key Points: First detailed geophysical model of the internal structure of the Mt. Melbourne Volcanic FieldMagnetic anomalies and rock magnetism data suggest the field is predominantly built‐up by reversely‐polarized volcanicsOur results support an establishment of the Mt. Melbourne edifice at least at the reverse polarity Matuyama magnetic epoch [ABSTRACT FROM AUTHOR]

The recent CDF‐II measurement of the W‐boson mass shows a strong tension with the corresponding Standard Model prediction. Once active neutrino masses are explained in the context of the Low‐Scale Seesaw mechanisms, this tension can be resolved. We investigate the possibility of explaining the longstanding muon anomalous magnetic moment anomaly within the same frameworks. We present a simplified extension of the Standard Model, accounting only for the second lepton generation, that describes a massive active neutrino and provides a combined solution to these anomalies. The model is renormalisable and introduces in the spectrum, beyond the sterile species of the Low‐Scale Seesaw mechanism, only one pair of exotic vector‐like leptons, doublets under the electroweak symmetry. We moreover discuss the extension of this model to the realistic three‐family case. [ABSTRACT FROM AUTHOR]

We report a systematic evaluation of the magnetic properties of FeAl2O4 focusing on the relationship between the fabrication conditions and its structural characteristics, in order to improve ceramics processing in applications of this material. For this purpose, the most important factor to control is the inversion parameter, expressed as y in the (Fe1−yAly)(Al1−y/2Fey/2)2O4 composition, which is relatively high for the spinel aluminate of a transition metal. The magnetic properties of these samples all show the spin glass phenomenon at low temperatures, and the cusp temperature depends systematically on this y value. This means that the evaluation of these magnetic properties will be an effective way to predict some characteristics of product FeAl2O4. Additionally, this study found an anomaly in the structural and magnetic characteristics of FeAl2O4 fabricated at a low temperature. This is thought to originate in a tiny and a small amount of impurity. It will be key for discussing the quality of chemically synthesized FeAl2O4, which is typically produced at low temperatures. [ABSTRACT FROM AUTHOR]

The unclear relationship between mineralization, hydrothermal alteration, and rock magnetization in volcanogenic massive sulfide (VMS) deposits limits us from fully understanding the magnetic anomalies and remagnetization process in this type of deposit. We address the issue by conducting systemic paleomagnetic, rock magnetic, petrographic, and X‐Ray diffraction studies in the Dapingzhang VMS deposit on the northwestern Indochina Block. Magnetite is the dominant magnetic carrier of hydrothermally altered surrounding rocks and orebody. Magnetite consumption and secondary magnetite formation occurred at different stages and types of hydrothermal alteration. The overall decrease in magnetite concentration from chloritization via silicification to mineralization implies that the magnetite was mostly consumed during hydrothermal alterations. Secondary single domain magnetite, which can carry a remagnetization direction, is proposed to be formed during illitization via the smectite‐to‐illite transformation. Secondary superparamagnetic magnetite, which was most likely formed during the late stage of chloritization, is unable to carry the stable characteristic remanent magnetization. The site‐mean direction of high‐temperature and high‐coercivity components is Dg/Ig = 324.5°/43.1°, and kg = 35.1, with α95 = 6.8° before tilt correction, and Ds/Is = 316.2°/37.6°, and ks = 16.4, with α95 = 10.1° after tilt correction, with a negative fold test. However, plate reconstruction is limited by the uncertainty of the tilting process following mineralization and the possibility of remagnetization during burial alteration. Therefore, this study provides a mechanism for rock magnetic variation and remagnetization during VMS mineralization. Plain Language Summary: We conducted paleomagnetic, rock magnetic, petrographic, and X‐Ray diffraction studies on volcanogenic massive sulfide (VMS) deposit to better understand the interaction between mineralization, hydrothermal alteration, and magnetization in this kind of deposit. Magnetite is the main magnetic carrier of orebodies and surrounding rocks. The overall decrease in magnetite concentration from chloritized samples to orebodies, via silicified samples, explains the low magnetic anomalies in VMS deposits. However, in samples containing a high concentration of chlorite, a significant amount of secondary superparamagnetic magnetite was discovered. Secondary single domain magnetite is ascribed to be formed through the transformation of smectite to illite during hydrothermal alteration, providing an explanation for remagnetization in VMS deposits. Therefore, magnetite consumption and secondary magnetite formation occurred during different types and stages of hydrothermal alteration. The site‐mean paleomagnetic direction is calculated, but it cannot be used in plate reconstruction due to the unclear bedding attitudes prior to mineralization and the possibility of remagnetization during burial alteration. This research improves our understanding of the processes of magnetic mineral variation and remagnetization during VMS mineralization. Key Points: Magnetite is the major magnetic carrier of hydrothermally altered surrounding rocks and orebodiesMagnetite consumption occurred from chloritization via silicification to mineralizationRock magnetism reveals the neoformation of superparamagnetic and single domain magnetite during chloritization and illitization, respectively [ABSTRACT FROM AUTHOR]

Marine magnetic anomaly strips are important for plate tectonic studies, thereby promoting the development of the geoscience revolution. Most previous studies typically consider a lava layer with vertical polarity boundaries as a simplified magnetic source layer. However, it cannot accurately explain the observed magnetic anomaly data; thus, complex oceanic crusts with multiple magnetic source layers, such as lava, dike, and gabbro layers, and various polarity boundary dip angles should be considered. To date, there is a lack of systematic understanding about how the dike and gabbro layers affect the total marine magnetic anomalies, particularly the effect of lava layers with different boundary inclinations on the intensity and polarity boundary of the magnetic anomaly. This study aimed to confirm the significance of these factors. Hence, we systematically simulated and analysed the magnetic anomaly characteristics with different inclination and magnetization settings for each layer using the forward modelling method and determined the impact of the complexity of the magnetic structure of the oceanic crust on the magnetic anomaly. Our results showed that the contributions of the dike and gabbro layers to the magnetic anomalies was up to 10%–30% and cannot be ignored. Moreover, the polarity transition point may shift with the inclination of the lava, dike, and gabbro layers but is insensitive to the magnetization of each layer. This study emphasizes the significance of the dike and gabbro layers and the inclination variations of different layers, which should be thoroughly studied. This study facilitates a reasonable interpretation of the magnetic structure of the oceanic crust and further refines the boundary of the magnetization zone with alternative polarity. [ABSTRACT FROM AUTHOR]

The Dead Sea Fault (DSF) is a crustal‐scale continental transform fault separating the African and the Arabian plates. Neogene to Quaternary volcanic activity is well‐spread in Northern Israel. Yet, the origin of the magmas that fed the eruptions is still unpinned. Our local earthquake tomography depicts velocity distributions typical of rifting settings. At 9 km depth, a prominent high Vp/Vs anomaly marks the presence of cooling melts. We propose that protracted transtension along the DSF caused crustal thinning promoting the emplacement of magmatic bodies. Crustal emplacements of magmas in Northern Israel reconcile multiple observations, including the high geothermal gradient, the prominent magnetic anomalies and the traces of mantle‐derived fluids in the springs across the Sea of Galilee. We provide a compelling evidence for rifting in segments of the DSF and identify the potential source of magmatism that fed part of the volcanic activity of the area. Plain Language Summary: The Dead Sea Fault (DSF) is a deep‐reaching fault separating the African and the Arabian plates. Geologically recent volcanic activity is well‐spread in Northern Israel but the origin of the magmas that fed the eruptions is yet to be found. We propose that protracted extensional motion along the DSF caused crustal thinning facilitating the emplacement of magmatic bodies in the crust. Our local earthquake tomography depicts velocity distributions typical of spreading margins. At 9 km depth, a prominent anomaly marks the presence of cooling melts. Crustal emplacements of magmas in Northern Israel reconcile multiple observations that are normally not common in sedimentary environments. The occurrence of magmas at depth would release fluids that would be compatible with the seismicity that sporadically affects the region. We provide a compelling evidence for rifting in segments of the DSF and identify the potential source of magmatism that fed part of the volcanic activity of the area. Our findings hold major implications for revisiting the natural hazard assessment of the Levant region. Key Points: Magma emplaced along the Dead Sea Fault (DSF)Localized rifting along the segment of the DSFOccurrence of cooling magmas may reconcile several geophysical, geological and geochemical observations in around the Sea of Galilee [ABSTRACT FROM AUTHOR]

The western segment of the suture zone between the Yangtze and Cathaysia blocks, which is the most important tectonic boundary related to the formation and rifting of south China, is enigmatic and not fully understood due to the sporadic exposure of Precambrian strata and ophiolites. Three‐dimensional electrical resistivity models derived from inversion of magnetotelluric data identified a lithospheric‐scale conductive zone extending northeastwards beneath the Youjiang basin, which was interpreted as the western segment of the suture zone. The high conductivity and coincident high magnetic anomalies closely match the location of Carlin‐type gold deposits, which can be explained by fluids and gold‐bearing sulfide minerals in a fossil suture zone. Inconsistent with the southeast‐dip resolved at the eastern segment of the suture zone (the Jiangshan‐Shaoxing fault) in the earlier study, the slightly north‐dipping geometry at the western suture zone implies the reactivation by northward subduction and closure of the Paleo‐Tethys Ocean. Plain Language Summary: Suture zones are tectonic scars that mark the subduction, collision, and amalgamation of different tectonic units. Imaging suture zones is critical because they are first‐order tectonic boundaries and can play a guiding role in continental rifting and breakup. The suture zone between the Yangtze and Cathaysia blocks is the most important tectonic boundary in south China. While the eastern segment of this suture zone is agreed to be located along the Jiangshan‐Shaoxing fault, the western segment of this suture zone is under debate. This study used magnetotelluric method to image the deep earth structure beneath the western boundary of the Yangtze and Cathaysia blocks. We identified a high‐conductivity zone from the subsurface to a depth of 80 km and interpreted this zone as being caused by fluids and gold‐bearing sulfide minerals in a fossil suture zone. The conductivity pattern observed in this suture zone differs from that in the earlier study about the eastern segment of the suture zone. This implies that the western suture zone has been modified after the initial collision of the two continents, perhaps by northward subduction and closure of the Paleo‐Tethys Ocean. Key Points: Magnetotelluric array data were inverted to obtain the lithospheric resistivity structure in southwestern ChinaThree‐dimensional resistivity model images a Precambrian suture beneath the Youjiang basinThe geometry resolved at the suture zone implies the reactivation by northward subduction and closure of the Paleo‐Tethys Ocean [ABSTRACT FROM AUTHOR]

Reeve et al. (2022) address the stratigraphic record of continental breakup by focusing on a set of stratigraphic unconformities from a proximal sector of the NW Australian continental margin, inboard from the Exmouth Plateau. They suggest that such unconformities can potentially document a well‐defined three‐stage process: end of the syn‐rift phase, formation of a wide continent‐ocean transition zone (COTZ) and generation of 'true' Penrose‐type oceanic crust. We counterargue that continental breakup is a protracted event that can only be understood via seismic‐ and chronostratigraphic correlations of strata, and their composing sequences, across and along rifted margins. Tying proximal stratigraphic unconformities to magnetic anomalies outboard from the study area in Reeve et al. (2022) is open to question. In parallel, we suggest that age resolutions of ca. 1 Ma are not achievable using the micropaleontological data presented in Reeve et al. (2022), with an important reworking of microfossil assemblages potentially occurring during the erosional process forming local and regional unconformities. Our discussion addresses these points in more detail. [ABSTRACT FROM AUTHOR]

The use of potential field methods for geophysical exploration purposes is nowadays quite common: these techniques consent to retrieve geological knowledge over extended regions and can give complementary information where other invasive or expensive techniques, such as seismic acquisitions, fail (e.g., in the recovery of geometries of geological horizons beneath a thick salt layer). Recent dedicated satellite gravity and magnetic missions, such as GRACE, GOCE and SWARM together with the exploitation of offshore satellite altimetry and airborne/shipborne surveys, have paved the way to the realization of a variety of global models, characterized by spatial resolutions of about 4 km (both for gravity anomaly and lithosphere magnetic anomalies) and high accuracy (about 3-5$3\text{-}5$ mGal and 20 nT). These models are a valuable source of information to study the geological evolution and characterization of the lithosphere structure, especially at a regional scale. In the present work, some preliminary technical aspects related to the use of these models to perform three‐dimensional inversion are discussed, thus defining an empirical but rigorous procedure to set up gravity and magnetic inversion. In particular, we address the questions whether the classical planar approximation is acceptable for regional inversions or if a spherical one is required. We also provide guidance for choosing the best gravity functional (e.g., gravity anomalies or second radial derivative of the anomalous potential) and the optimal sizing of the three‐dimensional volume area to be modelled depending on the specific target investigated. The application of the proposed methods to the Mediterranean case study is also presented. [ABSTRACT FROM AUTHOR]

Near‐real time analysis of magnetization can provide important information for the imaging of volcano systems and their spatiotemporal evolution. This study focuses on the contribution of volcano‐magnetic signals from reiterations of ground magnetic measurements to investigate the evolution of active structures at the Piton de la Fournaise volcano from 2017 to 2020. Changes are demonstrated by magnetic anomalies along a reference profile by means of the reiteration periods. These variations are first modeled qualitatively in 2D using electrical resistivity constraints in order to investigate the evolution of magnetization at depth through time, and the model is subsequently compared with the 3D intrusive activity from depth up to the surface from Interferometric Synthetic Aperture Radar (InSAR) inverse modeling. The shallow areas of demagnetization modeled from one reiteration to another are consistent with the geometry and location of the underlying intrusions revealed by the 3D InSAR models, suggesting strong thermal, stress, and electrokinetic effects due to magmatic activity not only at the surface but also at depth, along the main magmatic paths. It also raises a question as to the extent of the associated thermal diffusion processes at the scale of individual magma injections. This study confirms that detecting resistivity and magnetization anomalies, and quantifying their spatiotemporal evolution, can provide powerful tools for imaging volcanic systems at various scales and for providing warning of associated hazards. It also highlights the necessity for 4D monitoring of volcanic edifices using this method to provide greater precision, an important issue that is now made possible by the use of Unmanned Aerial Vehicle measurements. Plain Language Summary: Volcanic activity (through volcano‐tectonic, magmatic, and hydrothermal processes) undeniably disturbs the magnetic field, especially at a local scale. Recent studies have evidenced the potential of magnetic field measurements in imaging thermal anomalies (strong influence of temperature on magnetic measurements) and mechanical heterogeneities (fracturing‐alteration). Piton de la Fournaise (La Réunion Island, Indian Ocean) is an outstanding target to address such issues, being highly active and closely monitored. In this study, we used repeated magnetic measurements conducted over 3 years along a 3,780‐m‐length profile close to the summit of Piton de la Fournaise. We used the complementarities between magnetization and electrical resistivity parameters in a 2D magnetic modeling approach, in order to image the consequence of the eruptive dynamics on the edifice structure at depth. The temporal evolution of the magnetic anomalies appears strongly correlated to the depths and volumes of magmatic intrusions along the main active area. These results open new perspectives in studying the spatiotemporal changes in magmatic, hydrothermal, and mechanical changes and alteration processes within volcanic edifices. Key Points: Volcano‐magnetic variations at Piton de la Fournaise volcano (magmatic and mechanical changes, hydrothermal alteration processes)2D modeling of magnetic anomalies evolution under electrical resistivity constraints consistent with Interferometric Synthetic Aperture Radar 3D intrusions modelsImaging the main paths of weakness at depth that could be associated with potential future magmatic transfers [ABSTRACT FROM AUTHOR]

Previous works used marine magnetic survey data and interpreted magnetic anomalies related to seaward‐dipping reflectors (SDRs) as oceanic crust or SDR age constraints in the South Atlantic Ocean. However, we advise against using SDR‐related magnetic anomalies to constrain ages because of the mostly low‐dipping geometry causing the overlapping of rocks extruded during periods of different polarities. The data are difficult to interpret correctly because of the SDR compositional heterogeneity, sedimentary intercalations, variations in package thickness with different compositions and magnetic polarities, and the absence of a link between the SDR magmatic position and age. SDR‐related magnetic anomalies are mainly caused by magnetic susceptibility contrasts rather than remanent magnetism. Due to this complexity, the SDR geometry and variable composition make SDR‐related magnetic anomalies challenging to use for age constraints. The Pelotas Basin SDRs age cannot be estimated by magnetostratigraphy, and this method likely cannot constrain the age of any SDR wedge. Plain Language Summary: Since the 1960s, an increased understanding of oceanic crust chronology has quickly evolved into a field of study called magnetostratigraphy. Basaltic lavas extruded in a certain time interval acquire a positive or negative magnetic polarity according to the magnetic polarity on Earth during the extrusion. From the mid‐ocean ridge to the continental oceanic boundary, the continuous and progressive accretion of the oceanic crust provides age constraints for the sea bottom. However, on volcanic passive margins, the presence of volcanic rocks with wedge geometries is abundant. These volcanic rocks are called seaward‐dipping reflectors (SDRs) because of their wedge‐shaped geometry toward the ocean and are usually identified by seismic reflection surveys. The presence of these volcanic wedges makes the identification of the oceanic–continental crustal boundary a challenging task. Some magnetic anomalies that some researchers state as related to a regular vertical oceanic crust are SDR‐related. The SDR‐related magnetic anomalies are not related to that age because SDR‐related magnetic anomalies are mainly caused by magnetic susceptibility contrasts rather than remanent magnetism. We used seismic lines and magnetic data from the Pelotas Basin to illustrate how these magnetic anomalies are not age‐related. Key Points: Some magnetic anomalies interpreted as related to vertical fabric oceanic crust are related to seaward‐dipping reflectors (SDRs)Seaward‐dipping reflectors are different from typical oceanic crust in geometry and compositional heterogeneitySDR‐related magnetic anomalies should not be used to constrain ages [ABSTRACT FROM AUTHOR]

Solar wind ion sputtering is one of several non‐negligible loss mechanisms for water ice in permanently shadowed regions (PSRs) near the lunar poles. Previous estimates of the solar wind ion flux within south polar PSRs have considered only the ambient solar wind flow and effects of topography. Here, improved maps of crustal magnetic fields in the lunar polar regions are constructed, confirming that more anomalies are present near the south pole than near the north pole. These anomalies have moderate amplitudes, occur over at least two permanently shadowed craters, and correlate approximately with the exposed water ice distribution. Because of the low angle of solar wind incidence near the poles, these anomalies are likely effective in reducing the ion flux, and any resulting water ice loss rate. These anomalies may therefore explain why more water ice is found near the south pole than near the north pole. Plain Language Summary: Significant amounts of water ice are believed to be trapped in permanently shadowed regions (PSRs) near the lunar south pole. The extent to which water ice can survive in PSRs is limited by several factors, including the rate of sputtering losses from the solar wind ion bombardment. This loss rate has previously been estimated considering only the ambient solar wind flow and effects of topography. However, due to the low angle of solar wind incidence near the poles, even moderate magnetic anomalies may strongly deflect the ion bombardment within PSRs, helping to shield their interiors from ion sputtering losses. Here, new maps of crustal fields in the lunar polar regions are presented, confirming that more strong anomalies are present near the south pole than near the north pole, including over at least two permanently shadowed craters. These anomalies are about one‐quarter of the strength of the prototypical Reiner Gamma anomaly on the near side and should therefore be effective in shielding the interiors of these PSRs from the ion bombardment. The presence of stronger anomalies near the south pole than near the north pole may therefore help explain why more water ice is found near the south pole. Key Points: Moderately strong magnetic anomalies are present near the lunar south pole and correlate approximately with the ice exposure distributionThese anomalies are likely effective in reducing the solar wind ion flux and resulting water ice loss rate in permanently shadowed regionsThe presence of stronger anomalies over the south polar region than the north polar region may explain why more water ice is found there [ABSTRACT FROM AUTHOR]

Complementary independent and joint focusing inversion investigations are applied to the magnetic and gravity datasets for two kimberlite pipes, BK54 and BK55, in Botswana. The magnetic data are high resolution and, clearly, indicate two anomalies in the survey area. Independent inversion of this magnetic data provides a focused image of the subsurface with sharp boundaries for both pipes. The extensions of the pipes are close to those estimated by the available boreholes in the area. The spatial resolution of the gravity data is, on the other hand, relatively poor. The BK54 pipe does not appear on the residual gravity anomaly, while the BK55 is characterized by a positive anomaly. Independent inversion of the gravity data provides the geometry of the BK55 but does not identify the BK54 pipe. While there are some lower density materials in the place of the BK54 pipe, no specific target is revealed. Furthermore and relevant is that the reconstructed model for BK55 is not focused. A joint focusing inversion based on the structural cross‐gradient linkage is applied for the combined gravity and magnetic datasets. This algorithm produces structurally similar magnetic susceptibility and density models. A lower density distribution of material, similar to that of the magnetic susceptibility distribution, is revealed for the BK54 pipe. Moreover, in contrast to the result obtained by an independent inversion, the structure for BK54 is connected at depth, and the reconstructed models of BK54 and BK55 share the sparsity. The models are not as sparse as the magnetic susceptibility model that is obtained independently, but they are more focused than the independently obtained density model. A comprehensive comparison of the reconstructed models, and also computational CPU time, for independent and joint inversions is presented. [ABSTRACT FROM AUTHOR]

Two‐dimensional modeling of gravity and magnetic anomalies in terms of polygonal bodies is a popular approach to infer possible configurations of geological structures in the subsurface. Alternatively to the traditional trial‐and‐error manual fit of measured data, here we illustrate a probabilistic strategy to solve the inverse problem. First we derive a set of formulae for solving a 2.75‐dimensional forward model, where the polygonal bodies have a given finite lateral extent, and then we devise a Hamiltonian Monte Carlo algorithm to jointly invert gravity and magnetic data for the geometry and properties of the polygonal bodies. This probabilistic approach fully addresses the nonlinearity of the forward model and provides uncertainty estimation. The result of the inversion is a collection of models which represent the posterior distribution, analysis of which provides estimates of sought properties and may reveal different scenarios. Plain Language Summary: A probabilistic Monte Carlo method to infer the shape and properties of geological bodies in the subsurface from gravity and magnetic data is discussed in this paper. The geological bodies are represented as polygons with constant density and magnetic properties. The results of applying the proposed algorithm is a collection of models of the subsurface that can be statistically analyzed to infer structure and properties of the subsurface. Key Points: Contrary to the traditional manual approach, an objective procedure to jointly invert gravity and magnetic anomalies for 2.75D polygonsSampling using gradient information is an efficient nonlinear strategy to explore plausible solutions, where deterministic methods failInterrogation of the collection of posterior solutions provides statistical answers to complex questions including uncertainty estimation [ABSTRACT FROM AUTHOR]

Unmanned aerial vehicle (UAV)‐based magnetometer systems became more and more attractive for large‐scale archaeological prospection in recent years. Although their sensors exhibit the same sensitivity than the ground‐based prospecting systems, UAV prospecting is seriously handicapped by the magnetic and mechanical disturbances of the drone and by limitations of a low‐level flight. To minimize these disturbances, scalar magnetometers are attached only on a tether 2.5–10 m beneath the drone to be flown as close as possible above the ground. First, test measurements with UAV‐fixed fluxgate magnetometers provide more accurate results than the scalar magnetometers in any configuration but have to overcome disturbance by vibrations. Here, we present a case study choosing the compact set‐up of the Sensys MagDrone R4. The high sampling rate of 200 Hz of the three axis fluxgate sensors of the R4 allows sufficient filtering of the interferences generated by the UAV and external disturbances. High‐precision flight control of the drone allows operating the sensors by radar‐controlled flight height ∼1 m above the ground, which is a fundamental and indispensable prerequisite for archaeological prospecting. For our test, we choose the site Ganacker (southern Bavaria), where we expected a large range of archaeological structures and features with high magnetic contrast. We compare and verify the magnetogram with historical and recent geodata. Our results show that the R4 system offers an outstanding step forward regarding a successful application for archaeological prospection. Already now, the system is well suited for the fast mapping of large areas and archaeological sites with intense magnetic anomalies. [ABSTRACT FROM AUTHOR]

Magnetization is a natural property of magnetic materials which is widely used to analyze paramagnetic data, locate unexploded ordnance, explore mineral deposits and gas resources, and image anomalous magnetic structures in the Earth's crust. An essential and challenging task is to compute accurate magnetic anomalies caused by realistic magnetic 3D structures. In this study, for the first time, we derive the analytical expressions of magnetic potential, magnetic field and magnetic gradient tensor for magnetic materials with 3D polyhedral shapes and magnetization vectors that may vary in the space following polynomial trends. The order of polynomials can vary from one to high positive integers in both horizontal and vertical directions. Synthetic and realistic deposit models are used to validate our analytical solutions. We release the open‐source code in C++. Plain Language Summary: The geophysical magnetic exploration method is widely applied in the exploration of mineral deposits and gas resources, studies of sea‐floor spreading, detection of military and civilian magnetic objects, and Earth crust and other planets imaging. To interpret anomalous magnetic data acquired by ground, airborne, borehole, marine, and satellite magnetic surveys, geophysicists need to accurately compute the magnetic field and magnetic gradient tensor field of 3D magnetic structures with realistic magnetization. In this study, we successfully derive a set of closed‐form solutions of magnetic field and magnetic gradient tensor for 3D polyhedral structures with magnetization vectors which may vary in the space according to polynomial laws of arbitrary order. The intensity of magnetization can also vary in both horizontal and vertical directions. Based on the fact that 3D polyhedral bodies can well approximate arbitrary geometries of realistic structures and polynomial magnetization variations can well represent arbitrary distributions of magnetization, our closed‐form solutions could accurately compute the magnetic field and magnetic gradient tensor caused by realistic geological rocks and would play an essential role in the magnetic exploration method. Key Points: Closed‐form solutions of magnetic field and magnetic gradient tensor are derived for 3D polyhedral structures with complicated magnetizationThe magnetization in polyhedrons can vary in both horizontal and vertical directionsOpen source C++ software is free to use [ABSTRACT FROM AUTHOR]

Axial Seamount in the northeast Pacific erupted in 2015, 2011, and 1998. Although monitored by the Regional Cabled Array of the Ocean Observatory Initiative, few magnetic surveys have been conducted over the region. This study uses high‐resolution magnetic data over the seamount collected by autonomous underwater vehicle Sentry during three years (2015, 2017, and 2020). The goal is to investigate whether there are temporal changes in the near‐surface magnetic field observable over the time scale of one volcanic cycle. We compare magnetic maps from repeated tracklines from each year. We find maps of the yearly difference in magnetization show coherent patterns that are not random. The central region of the caldera has become more magnetic during recent years, suggesting cooling of the surficial lava flows since 2015. Sentry data are more sensitive to shallow crustal structure compared to sea surface data which show longer wavelength anomalies extending deeper into the crust. Plain Language Summary: Axial Seamount is an active underwater volcano located off the coast of Oregon that has recently erupted in 2015, 2011, and 1998. Though Axial is monitored by many seafloor instruments, the magnetism of the region and how it changes with time has not been studied. However, we believe studying the magnetics of Axial can provide powerful insights into the internal structure of the volcano. Specifically, volcanic rocks contain magnetic minerals called magnetite. Above a certain temperature, called the Curie temperature, these minerals become non‐magnetic. Thus, magnetism may be able to detect changes in the high temperature areas of the volcano between eruptions, such as the magma chamber or young lava flows. Here, we perform the first study analyzing three separate years of high‐resolution magnetic data collected using an autonomous underwater vehicle over Axial seamount. We create magnetic maps using repeated vehicle tracklines to highlight differences between each year and compare our findings with broader surveys of the region. Our results indicate the central region of Axial has become more magnetic during recent years, suggesting cooling of the lavas erupted in 2015 and their associated subsurface feeder zones. Key Points: Repeat magnetic surveys at active submarine volcanos image temporal change in thermal structure related to geologic and volcanic processesHigh resolution magnetic data can be used for low‐cost volcano monitoring in the marine environment over relevant timescales [ABSTRACT FROM AUTHOR]

Magnetic data can be acquired from a number of different platforms (e.g., ground, drone, helicopter) using a variety of sensors (e.g., caesium vapour‐type optically pumped magnetometers, fluxgate, superconducting quantum interference devices) with different flight line configurations. To detect a magnetic anomaly associated with a mineral commodity that is not exposed but is thought to be associated with the anomalous magnetic mineral content, it is necessary to optimize the survey parameters through a complete data integration process. Prior petrophysical measurements provide insight into the physical contrast that might be expected between adjacent lithologic units and between the ore zone and the encompassing lithology. Oriented rock samples provide access to magnetic remanence data through palaeomagnetic laboratory measurements. Knowing the typical morphology of the ore zone one can compute a forward model of the expected anomalous response and determine which combination of survey parameters provides the highest probability of detecting the commodity being sought. In this study, we analyse magnetic patterns associated with thin dipping skarn bodies from the Geyer mining district in Erzgebirge, Germany. Petrophysical measurements indicate that the skarns are more magnetic than the surrounding host rock. Partially oriented samples from a bore core record a Variscan age metamorphic remanence. Forward modelling indicates that clusters of skarn bodies are required to produce a reliably detectable magnetic signal. Ground, or low elevation drone surveys are needed to detect these anomalies with standard scalar‐type optically pumped magnetometer or fluxgate magnetic surveys. The enhanced spatial resolution and long‐wavelength rejection of a superconducting quantum interference device based full‐tensor magnetic gradiometer provide an improvement over optically pumped magnetometers for an aircraft‐based survey platform. [ABSTRACT FROM AUTHOR]

Three‐dimensional (3‐D) inversion of regional lithospheric magnetic anomaly data not only needs to be performed in the spherical coordinate system but also requires valid constraint information to suppress the nonuniqueness. We present a constrained inversion approach of regional magnetic data at near‐surface altitudes to recover a 3‐D susceptibility model in spherical coordinates. First, we use a synthetically forward modeling experiment to illustrate that a 3‐D model with susceptibility variations along the depth direction should be considered when the altitude of magnetic data is 5 km above the WGS84 ellipsoid. We then choose the least‐squares algorithm to recover the lithospheric susceptibility model. Meanwhile, a model objective function including sensitivity‐based weighting function and bottom depth constraint of the source (i.e., Curie point depth, CPD) is introduced to stabilize the inversion and guide an optimal solution. Both the synthetic test and the application to the real data over the Northern Xinjiang indicate that the constrained inversion approach is effective to obtain a geologically reasonable result above the CPD. The recovered 3‐D susceptibility distribution under the Northern Xinjiang corresponds well to the extension of the main tectonic frame. All the rigid and cold blocks are imaged as high‐susceptibility anomalies, whereas the pronounced low‐susceptibility anomalous body is observed beneath the Tianshan. In addition, the earthquakes are mostly (>95%) located in areas where the susceptibility is smaller than 0.03 SI and vertically integrated susceptibility is smaller than 0.8 SI· $\cdot $km. Plain Language Summary: Magnetic susceptibility is an important physical parameter of rocks in the lithosphere. Obtaining the lithospheric susceptibility distributions not only can help to describe the lithological and temperature architectures as well as understand the geological structure, evolution history, and mantle dynamics, but also is useful for natural hazards (e.g., earthquakes and volcanos) studies and explorations of metallic mineral and geothermal resources. Inversion of the lithospheric magnetic data is an effective approach to recover the three‐dimensional (3‐D) susceptibility model of the lithosphere. Especially for regional and even global studies, the proposed 3‐D inversion approach not only needs to be performed in the spherical coordinate system but also requires valid constraint information (e.g., the bottom of the magnetic layer) to suppress the nonuniqueness. This approach is first tested by using a synthetic susceptibility model and then applied to the magnetic anomaly over Northern Xinjiang in northwestern China. Both the results show that the constrained inversion obviously improves the reliability of the 3‐D susceptibility imaging. The recovered 3‐D susceptibility structure corresponds well to the extension of the main tectonic units. The proposed inversion approach will be submitted as an open‐source program and be updated for efficiently continental even global scale applications. Key Points: A constrained approach by Curie point depth (CPD) for the 3‐D inversion of lithospheric magnetic anomaly data in a spherical coordinate system is proposedCPD distribution and 3‐D susceptibility structure of the Northern Xinjiang are constructed using WDMAMv2 and LCS‐1 modelsThe recovered 3‐D susceptibility model of the Northern Xinjiang has a high vertical resolution and correlates well with the tectonic units [ABSTRACT FROM AUTHOR]

In aeromagnetic measurement, accurate compensation for the interference magnetic field generated by the aircraft platform due to the aircraft maneuvering in the Earth's magnetic field is an important prerequisite for the accurate identification of the magnetic anomaly signal of the detection target. The flaws of the traditional calibration flight scheme in aeromagnetic interference compensation are firstly analyzed, and then an improved scheme is proposed, featuring smaller calibration flight areas, more simplified maneuvers, shorter flight route and less influence from the magnetometer's direction and extreme weather. The improved scheme can enhance the robustness of the aeromagnetic interference compensation matrix and improve the compensation efficiency, and thus both the solved magnetic compensation coefficients and compensation effects are significantly improved. The experimental results of the aeromagnetic interference compensation in an area of Inner Mongolia of China show that the average accuracy of the repeated survey lines, which are compensated by the improved scheme, can be increased by 5 and 3 nT, respectively, compared with the uncompensated results and the results compensated by the traditional scheme. Therefore, the effectiveness and superiority of the improved calibration flight scheme is fully proved. Plain Language Summary: Aeromagnetic measurement technology is the most economical and effective technical means to obtain high‐precision and high‐resolution geomagnetic information. Because the aircraft used in aeromagnetic measurement is composed of ferromagnetic materials, it will produce an interference magnetic field when maneuvering in the Earth's magnetic field. In order to obtain pure geomagnetic field measurement data, it is necessary to compensate the interference magnetic field. The traditional calibration flight scheme is widely used in the aeromagnetic interference compensation, and has played an important role in the existing aeromagnetic measurement. However, with the continuous improvement of the measurement accuracy of airborne magnetometers, there are higher requirements for calibration, and some defects of the traditional calibration flight scheme are found in practice. Hence, an improved calibration flight scheme is proposed in this paper, which features smaller calibration area, shorter flight route, simplified maneuvers and less influence from the direction of the magnetometer. The experimental results show that the modified scheme can improve the average accuracy of repeated survey lines by 3 nT compared with the traditional one. Therefore, the improved scheme can be directly applied in the aeromagnetic interference compensation of scalar, vector and gradient magnetic measurement of manned and unmanned aerial vehicle (UAV). Key Points: An improved calibration flight scheme is proposed in the aeromagnetic interference compensationEffectiveness and superiority of the improved calibration flight scheme are validated by actual flight dataCompared with the traditional scheme, the improved one can increase the average accuracy of repeated lines by 3 nT [ABSTRACT FROM AUTHOR]

The article presents the results of archaeological prospection of site Dračevica (Donji Radišići, Ljubuški municipality, West Herzegovina Canton, Bosnia and Herzegovina) which was partly excavated in the late 19th century and so far has been interpreted as a Roman villa, possibly with a special function (road station) and a name attested in ancient sources (Bigeste). Through the use of various nondestructive prospecting methods (aerial photogrammetry, fieldwalking survey, magnetic susceptibility, magnetometry, earth resistance), precise location with RTK GNSS and integration of the data in GIS, the site was restudied and reinterpreted. It was established that the structures are not isolated, as was assumed in the earlier research but rather were a part of a much larger Roman settlement. The research proves that the internal spatial division of the site is more complicated than previously thought, consisting of several building complexes located along a road, as well as land division systems. Such settlement pattern suggests similar, average‐sized land plots and farms. The importance of the research lies also in the methodological approach and the outcome of the geophysical research. Our research was the first application of nondestructive methods of archaeological prospection on Roman sites in the karst landscapes of West Herzegovina, proving the usefulness of the applied methodology in these specific and difficult conditions. We have found dependencies in between the geological background (thin layer of low resistive, colluvial soil on shallow limestone bedrock and the occurrence of highly magnetic terra rossa, formed on weathered limestone) and the geophysical responses registered by various instruments, that is, moderate to good magnetic and electric contrasts between the features and their surroundings, with relatively strong anomalies from geological features. The most important was finding relationships between particular magnetic and electrical anomalies and the presence of very shallow bedrock or faint archaeological remains (e.g. limestone walls). Our methodology, as well as some of our interpretations, will be helpful as a reference for further surveys in the region. [ABSTRACT FROM AUTHOR]

The North Singhbhum Mobile Belt (NSMB) that lies in the Eastern Indian Shield between the Chotanagpur Granite‐Gneiss Complex (CGGC) and the Singhbhum Craton (SC) provides a unique opportunity to understand the Proterozoic crustal evolution of the Indian shield. In the present study, an integrated interpretation of petrophysical, Bouguer gravity, and aeromagnetic data was carried out to examine the crustal architecture and structural framework of the region. Three‐dimensional (3‐D) inversion of the aeromagnetic anomalies reveals that the magnetic basement depths range from 0.2 to 9.0 km in the region. The crustal models obtained from two‐dimensional (2‐D) and 3‐D forward modelling of potential field data reveal the Moho at 37–38 km depth beneath the NSMB and at a relatively deeper depth of 39–40 km and 40–44 km beneath SC and CGGC, respectively. Further, the distinct gravity high and the coinciding bipolar magnetic anomalies associated with the Dalma Formation can be attributed to the mafic/ultramafic intrusions. Gravity models across the Singhbhum Shear Zone (SSZ) and South Purulia Shear Zone (SPSZ) exhibit the crustal density inhomogeneity and Moho offset, typical of ancient suture zones of Precambrian terrains. In comparison, the absence of such crustal‐scale signatures across the North Purulia Shear Zone represents its intracratonic nature. Further, the Bouguer gravity and aeromagnetic signatures across the SPSZ, together with the crustal architecture and metamorphic ages, suggest that SPSZ marks the eastward continuity of the Gavilgarh‐Tan Shear Zone along which the amalgamation of northern and southern Indian cratonic blocks possibly took place at ca. 1.0–0.9 Ga. [ABSTRACT FROM AUTHOR]

With no significant topographic expression and limited bedrock exposure, the ~10 km diameter Karla impact structure (Tatarstan, Russia) is poorly known. The age of the impact is also poorly constrained stratigraphically to between 4 and 60 Ma, even if an upper Miocene age is more likely. Targeted gravity and magnetic field surveys were conducted over Karla to explore its size and structure in 2019. Bouguer gravity anomaly data reveal a central positive (+2 mGal) peak ~2 km in diameter surrounded by a concentric negative (−1 mGal) anomaly extending to ~3 km radius; a more irregular, outward‐decreasing (+1 to −1 mGal) positive anomaly extends to 6–8 km radius. A complex impact structure with diameter of 8–10 km is consistent with the Bouguer anomalies. Magnetic field data show 1 to several km‐wavelength anomalies with amplitude variation from +150 to −150 nT and little concentric structure, although the impact feature broadly corresponds to a magnetic low with a weak central high. A 2‐D numerical model of the structure was built using these potential‐field data and petrophysical properties measured on collected samples. It confirms a central uplift composed of Paleozoic sediments and Archean crystalline basement up to 1 km of depth. A 500 m deep collapsed disruption cavity filled by breccia and lacustrine deposits accounts for the Bouguer negative ring. The reversely polarized and weak central magnetic anomalies are controlled by the geometry of the crystalline basement associated with the deformation during the central uplift. [ABSTRACT FROM AUTHOR]

Magnetic anomalies commonly contain anomalies generated by crustal rocks that have variable mineral compositions and natural remanent magnetizations. Recovery of magnetic parameters from superimposed magnetic anomaly sources is therefore important for mineral exploration and geological studies. Superposition of magnetic anomalies leads to nonnegligible errors of inversion and interpretation. Therefore, extraction of magnetic anomalies is essential for magnetic data processing; however, existing methods cannot extract magnetic anomalies caused by sources without substantial depth differences. A novel low‐rank method is proposed for extracting a target magnetic anomaly from a superimposed anomaly. The low‐rank feature of the magnetic anomaly is used to obtain the target anomaly by reducing the Schatten‐p norm of the superimposed anomaly according to the possible target source distribution. The target magnetic anomaly can then be extracted from the data generated by the source interference at the same or different depths. The accuracy of the proposed method was verified using synthetic modeling. Magnetization vector information for individual igneous rocks was recovered from extracted magnetic anomalies via 3‐D inversion of field data from Yeshan (eastern China) that contain complex magnetic anomaly superpositions. The distributions and lithologies of five buried igneous rocks, including basalt, diabase, and granodiorite, were then identified. The proposed method expands the problem of separating magnetic information from rocks in different layers with large depth differences to rocks within the same or other layers and recovers geometric and physical information for each targeted magnetic source from the superimposed anomaly. Plain Language Summary: Magnetic rocks inherit different magnetic characteristics that depend on the type of rock and the features of the geomagnetic field present when the rock formed. Even for rocks at the same locality, the magnitude and direction of the magnetic vectors caused by the rocks are often different. Magnetic field observations contain mixed magnetic information from the geomagnetic core field and from all the rocks under and near the observation area, which causes serious problems for certain types of geological study. Therefore, we developed a new method to recover the magnetic anomaly caused by a target source from mixed magnetic information. We explain how the proposed method works and present a mathematical model. The robustness of the parameters of the proposed method is assessed using synthetic models. Synthetic experiments designed to test the accuracy of the proposed method indicated that the magnetic anomaly of the target rock could be recovered with high accuracy. Finally, we applied the proposed method to study field magnetic information in Yeshan, eastern China. Five magnetic anomalies caused by five isolated rocks were obtained using the proposed method, and the magnetic information, distributions, and lithologies of the five rocks were determined. Key Points: Magnetic data contain superimposed signals from multiple rocks that make extraction of magnetic anomalies for targeted sources challengingA novel low‐rank framework is proposed to extract target anomalies from superimposed magnetic anomaliesDetailed information derived from superimposed anomalies includes a magnetization vector model for each target source [ABSTRACT FROM AUTHOR]

The Antarctic Digital Magnetic Anomaly Project's first‐generation magnetic anomaly map (ADMAP‐1) was produced for the region south of 60°S from about 1.5 million line‐kms of airborne and marine magnetic anomaly data (Golynsky et al., 2001; https://www.bas.ac.uk/data/our‐data/maps/thematic‐maps/admap‐magnetic‐anomaly‐map‐of‐the‐antarctic/). The second‐generation ADMAP‐2 compilation (Golynsky et al., 2017; https://doi.org/10.22663/ADMAP.V2) incorporated an additional roughly 2.0 million line‐kms of airborne and marine magnetic anomaly data from international mapping through 2015. The present study integrates satellite magnetic observations from the Swarm mission with the near‐surface data of ADMAP‐2 to help fill the regional coverage gaps and better define the altitude behavior of the Antarctic's magnetic anomalies for enhanced geological analysis. The resulting satellite magnetic data‐supplemented compilation, ADMAP‐2s, yields further constraints on the enigmatic geology of the Gamburtsev Subglacial Mountains, Prince Charles Mountains, Wilkes Land, Dronning Maud Land, and other poorly explored Antarctic areas. It offers insights on the global tectonic processes and crustal properties of the Antarctic and helps to unify disparate geologic and geophysical studies by linking widely separated outcrops. It also supports studies on the geological controls of the Antarctic ice sheet, the crustal transitions between Antarctica and the adjacent oceans, and the geodynamic evolution of the Gondwana and Rodinia supercontinents. Plain Language Summary: This study integrates the second‐generation magnetic anomaly compilation with Swarm satellite magnetic data to offer important new constraints on the geology of the Antarctic's crust that is largely hidden beneath a pervasive blanket of seawater, ice, and snow. The satellite data‐supplemented magnetic anomaly compilation links widely separated outcrops to facilitate enhanced understanding of the lithospheric transition between Antarctica and its adjacent oceans, as well as the Antarctic's role in the tectonic evolution of the Gondwana and Rodinia supercontinents. The satellite data‐supplemented magnetic anomaly compilation in combination with complementary geological information, and ice‐probing radar, gravity, and other geophysical data enhances understanding Antarctic crustal rifting, mountain building and basin formation, plate subduction and accretion, and other regional lithospheric processes. Key Points: Swarm satellite magnetic gradient anomaly observations provide useful constraints to help fill regional coverage gaps in the more than 3.5 million line‐km of ship and airborne magnetic anomaly data of the ADMAP‐2 compilation. They also substantially enhance Antarctic crustal studies of the near‐surface magnetic survey dataOnshore, the ADMAP‐2 anomalies over West Antarctica include the effects of extensive late Cenozoic volcanic rocks within the West Antarctic Rift System and Mesozoic arc magmatism and terrane accretion along the paleo‐Pacific active margin of Gondwana. Over East Antarctica, they mark the Mawson Craton's southernmost boundary along 85.5°S between 157°E to 135°E to suggest that the Shackleton Ranges may not be part of the craton (Boger, 2011)Offshore, the ADMAP‐2s anomalies illuminate Antarctica's continent‐ocean transition zones. Satellite magnetic anomaly maxima also map enhanced crustal heat flow variations that yield relatively marginal signatures in the near‐surface obserations [ABSTRACT FROM AUTHOR]

The capacity of oceanic crust to record geomagnetic polarity reversals makes sea‐surface magnetic anomalies an essential tool to study plate tectonics. The anomalies are usually well‐defined at magmatic spreading centers, but are distorted and eventually disappear on magma‐poor mid‐ocean ridges such as the ultraslow Southwest Indian Ridge (SWIR), making their interpretation difficult. We attribute the variability of the SWIR sea‐surface magnetic anomalies to the alternance of magmatic spreading and detachment faulting. A three‐layer magnetic model is used to simulate the influence of such an alternance on the sea‐surface magnetic anomalies. Conversely, observed magnetic profiles at the SWIR are modeled to unravel their off‐axis crustal structure and past mode of spreading. The intruding gabbro bodies on the footwall of detachment faults play a major role in explaining the variability of sea‐surface magnetic anomalies at slow and ultraslow spreading ridges. Plain Language Summary: Marine magnetic anomalies result from the capacity of oceanic crust to record the ambient geomagnetic field polarity at the time of its formation at mid‐ocean ridges. These anomalies are usually well‐defined on magmatic crust formed at faster spreading ridges, but they are more elusive on magma‐poor crust of slower spreading ridges. Previous magnetic studies on the ultraslow spreading Southwest Indian Ridge show magnetic anomalies that are hardly identifiable on some segments. We investigate the hypothesis that the variability of the marine magnetic anomalies on this ridge results from the alternance of two modes of spreading. In the first one, seafloor spreading is achieved through the formation of magmatic crust, in the second one through detachment faulting which exhumes mantle rocks and intrusive gabbro bodies in a magma‐poor environment. Serpentinized mantle does generally not record accurately the geomagnetic polarity, so magnetic anomalies over the detachment faults rely on the intrusive gabbro bodies, capable to record the magnetic polarity. The quality of the magnetic signal depends on the abundance of these gabbro bodies, which in turn reflects the local degree of magmatism. We use forward modeling to simulate and confirm these hypotheses and test their reliability on observed magnetic profiles. Key Points: The variability of sea‐surface magnetic anomalies at ultraslow spreading centers reflects different degrees of magmatism along the ridgeGabbro bodies intruding the footwall of detachment faults partially record the magnetic polarity when this mode of spreading is activeSea‐surface magnetic anomalies may represent a tool to estimate the spreading mode at ultraslow spreading centers [ABSTRACT FROM AUTHOR]

The scattering of light off the bright regions of lunar swirls suggests a relatively higher fraction of fine‐grained dust compared to dust with similar optical maturity values found elsewhere on the lunar surface when assuming an isotropically oriented dust distribution, without preferred grain orientation. Here we propose a mechanism by which the ferromagnetic lunar fines, lofted by electrostatic effects or by meteoroid impacts, may rotate in a lunar magnetic anomaly and, upon landing, produce patches of organized alignments, generating anisotropic surface structures. We simulate these rotations for Reiner Gamma and provide a proof of concept for such a dust rotation model. While the magnetic forces remain negligibly small to influence the trajectories of the lofted particles, the magnetic torques have a significant effect on the rotation of magnetized dust, and can generate an organized landing pattern for elongated lunar fines, which offers a possible explanation for the lunar albedo patterns. Plain Language Summary: Lunar swirls are one of the most striking albedo features on the surface of the Moon. Light scattering of the bright regions of swirls suggest the presence of a relatively higher fraction of fine‐grained dust compared to dust with similar optical properties found elsewhere on the lunar surface when assuming an isotropically oriented dust distribution without preferred grain orientation. Here, we investigate a mechanism by which magnetized lofted dust may generate anisotropic surface structures. We simulate these rotations for the Reiner Gamma region and provide a proof of concept for such a dust rotation model. While the magnetic forces remain negligibly small to influence the trajectories of the lofted particles, the magnetic torque can influence the landing pattern, offering a possible explanation for the lunar albedo patterns. Key Points: We propose a rotation model in which the orientation of elongated dust particles becomes organized by magnetic fields in the lunar regolithThe rotation dynamics of lofted magnetized dust can produce surface structures by capturing an imprint of the magnetic field directionality [ABSTRACT FROM AUTHOR]

Scanning magnetic microscopy (SMM) is a modern magnetometry technique that maps the magnetic anomalies resulting from small‐scale variations of remanent magnetization within a sample. This information is vital to understand the origin of rock behavior in laboratory experiments and in larger scale magnetic surveys. To quantify the fine‐scale remanent magnetization, we used 3D magnetic vector inversion to jointly invert SMM data collected both above and below a 5 mm‐thick norite sample from the Bjerkreim‐Sokndal layered intrusion in South Norway. The sample is from an area with a striking remanent aeromagnetic anomaly which shows a minimum of −13,000 nT below background in the high‐resolution helicopter survey. Inversion results confirm bulk remanent magnetization measurements with calculated median magnetization intensities between 79 and 106 A/m and a strong preferred magnetization direction perpendicular to the slab plane. Furthermore, results indicate that the main source of natural remanent magnetization is in the pyroxenes. Plain Language Summary: Retrieving the small‐scale variation of the magnetization of a rock sample helps to identify the mineral phases containing the magnetization, and to evaluate their relative contribution to total bulk magnetization. This information can be used to understand the magnetic history of a sample and its geological setting. Today, rock samples can be magnetically scanned in a laboratory using a scanning magnetic microscope. This microscope measures the magnetic field at closely spaced points in a plane less than 1 mm from the sample surface. The main challenge in interpreting these results is the incorporation of additional information about the sample to yield a robust, constrained and reliable model. Here, we applied a 3D magnetization vector inversion (a sophisticated imaging method) and incorporated constraints for testing different hypothesis. We found that the magnetization inversions fit the data accurately and lead to bulk properties estimates consistent with those reported by previous studies. Key Points: Magnetic data and microscopic inspection indicate the main source of remanent magnetization is oxide exsolution lamellae in pyroxenesSimultaneous inversion of scanning magnetic microscopy data acquired above and below the sample indicate heterogeneous magnetizationMagnetic inversion results are consistent with sample's bulk remanent magnetization measurements [ABSTRACT FROM AUTHOR]

Mars has a magnetic field originating in its strongly magnetized crust that holds clues to the planet's interior. We apply vector spherical harmonic decomposition to simple candidate magnetic structures to separate the parts responsible for the anomalies from those that remain invisible. A uniform magnetic layer produces no anomalies: spatial variations are essential although secondary magnetization does produce a weak field that might reflect the primordial dynamo field. A hemispheric layer produces anomalies confined to the equator rather than the observed hemispheric difference. A uniformly magnetized crust with variable thickness determined from gravity and topography produces a crustal field with large anomalies at the major impact crater sites that are not observed. These anomalies are not present if the magnetic layer lies deeper than the crater floor. We conclude that decomposing magnetizations in this way is a useful tool in the interpretation of Martian magnetic anomalies. Plain Language Summary: Four billion years ago Mars had a magnetic field generated by a dynamo operating in its liquid core, as Earth has today. It cooled faster than Earth and dynamo action ceased but not before it had magnetized the planet's crust. This study is made topical by the arrival of the Chinese rover Zhurong, which is capable of carrying out a ground magnetic survey. The lander InSight recorded a magnetic field some 10 times stronger than expected from measurements made by satellite in orbit. Here we use a relatively new technique to separate proposed magnetic structures into their "invisible" and "visible" parts. We show this while the magnetic field is stronger in the Southern Hemisphere than the North, this does not imply one hemisphere is more strongly magnetized than the other. Strong ground measurements can be explained by a strongly magnetized, invisible, shell that has been broken up into smaller, visible, fragments. Larger impact craters have no magnetic anomaly, an observation often attributed to removal of the original magnetized material; we show the anomaly remains if the surrounding crust is strongly magnetized and propose the source of the anomalies lies deeper than the bottom of these craters. Key Points: Vector spherical harmonic analysis can help elucidate magnetic structures in Mars' crustSecondary magnetization in a uniform shell produces a magnetic anomaly that reflects the original dynamo fieldAbsence of anomalies at large impact craters cannot be explained by simply excavating magnetized crust [ABSTRACT FROM AUTHOR]

The southern Indian Ocean has several prominent aseismic ridges recognized as oceanic large igneous provinces (i.e., the Madagascar Ridge, Del Cano Rise, Crozet Plateau, and Conrad Rise) in the off‐axis areas of the Southwest Indian Ridge (SWIR). However, previously obtained magnetic survey lines are sparse and not correctly aligned with the seafloor spreading direction; thus, the detailed spreading history, including the formation of these aseismic ridges, remains an open question. We reconstructed the tectonic history of two segments between the Discovery II and Gallieni fracture zones in the SWIR using newly obtained magnetic data (total and vector magnetic field) and an open‐source magnetic data set. We revealed that the southern Madagascar Ridge and the Del Cano Rise once formed a single bathymetric high and separated by at least Chron 30y, which is quite different from the global age model. In addition, the rises may have formed before Chron 34y, assuming an extinct ridge south of the Del Cano Rise. The two rises have been recognized as having formed by Marion hotspot plume‐induced excess volcanism around the active spreading ridge of the SWIR, which can explain locally isostatically compensated thicker‐than‐normal crust. However, linear magnetic anomalies have not been observed across the main part of these rises, suggesting that magmatic activity controlled by seafloor spreading is unlikely. Like other aseismic ridges in the southern Indian Ocean, these two rises may possibly have been formed partly by continental fragments rather than plume‐induced excess volcanism. Plain Language Summary: The southern Indian Ocean contains several bathymetric high regions previously interpreted as oceanic large igneous provinces. Hotspot‐ridge interaction is considered as the key factor in the formation of such large volcanic structures. However, the detailed seafloor spreading history and origin of these large volcanic structures are not understood as well as those in other oceans because of the vast and remote Indian Ocean. We conducted magnetic surveys and reconstructed a new tectonic history of two segments along the Southwest Indian Ridge (SWIR). We found that the southern Madagascar Ridge and the Del Cano Rise once formed a single bathymetric high and that they separated by at least 66 million years ago. Moreover, the rises may have formed before 84 million years ago, assuming an extinct ridge south of the Del Cano Rise. The two rises might have formed by interaction between the Marion hotspot and SWIR; however, linear magnetic anomalies implying seafloor spreading are not observed in the main parts of these rises. This absence suggests that hotspot‐ridge interaction cannot fully explain the origin of these rises. We cannot exclude the possibility that the two rises are partly continental fragments rather than products of hotspot‐induced excess volcanism. Key Points: Revised seafloor ages up to Chron 31 in the Indian Ocean are obtained by new total and vector magnetic dataOur new tectonic scenario indicates that the Madagascar Plateau and Del Cano Rise once formed a single bathymetric highThe tectonics of oceanic plateaus in the Indian Ocean need to be reexamined, including continental fragment origin [ABSTRACT FROM AUTHOR]