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The article presents the results of a qualitative and quantitative analysis of the geomagnetic field of the Ukrainian Carpathians and 3D magnetic modeling along the PANCAKE geotransect and Transcarpathian Depression, as well as a comparison of the obtained results with fault-block tectonics, deep structure, and distribution of a number of types of endogenous ore deposits and hydrocarbon accumulations. It is shown that the overthrust northeastern part of the Carpathian arc lies on the magnetic crust, and the southwestern one — on its non-magnetic lower part, and between the Rava-Rus’ka and Krakovets and Pre-Carpathian faults, the Earth’s crust is magnetized throughout. For the territory of the Transcarpathian Depression, the regional and local components of the geomagnetic field were identified for the first time, geological and geophysical characteristics were provided, and their tectonic interpretation was proposed. A three-dimensional magnetic model of the Transcarpathian Depression was created taking into account the magnetization of rocks according to measurements. A detailed magnetic model of the upper part of the crustal section of the Transcarpathian Depression was developed. The connection of magnetic sources with fault zones was analyzed; the results were compared with the deep structure and distribution of ore deposits and hydrocarbon accumulations. The regional source with magnetism І=1.0 A/m is located within the Mukachevo Depression and is located at a depth of 6.0 km to 13 km. The local component of the geomagnetic field reflects the magnetic inhomogeneity of the Earth’s crust in the upper 3—4 km of the section and mainly reflects the volcano-tectonic structures and dike formations of the Vyhorlat-Gutyn Ridge, the Chop-Berehove Uplift, and the Velika Dobron’ Uplift. The maximum depths of magnetic sources (up to 3.5 km) and their magnetization (1.22 A/m) are characteristic of the structures of the Vyhorlat-Gutynsky Ridge, intermediate values of depths (2.0—3.0 km) and magnetization (up to 0.93 A/m) belong to the Chop-Berehove Uplift, and the minimum depths (up to 1.1 km) and magnetization (up to 0.7 A/m) are characteristic of the Velika Dobron’ Uplift. It is shown that the gas fields of Transcarpathia correspond to local positive magnetic anomalies and are localized above a deep magnetic source. Within the Berehove Uplift, positive anomalies and magnetic sources indicate andesiteporphyrite shafts and andesite domes of Sarmatian age associated with gold, gold-polymetallic and silver mineralization. A zone of antimony mineralization is associated with the Pannonian-Pontic volcanic structures along the southern foot of the Vyhorlat-Gutyn Ridge, and deposits and occurrences of bismuth and mercury correlate well with intrusive formations of the Dacian-Romanian age.

We present new palaeomagnetic and rock magnetic results with a stratigraphic interpretation of the late Early-Middle Pleistocene deposits exposed on the left bank of the River Danube at Dolynske, southern Ukraine. A thick succession of water-lain facies is succeeded by reddishbrown clayey soils, topped by a high-resolution loess-palaeosol sequence. These constitute one of the most complete recently discovered palaeoclimate archives in the Lower Danube Basin. The suggested stratigraphy is based on the position of the Matuyama-Brunhes boundary, rock magnetic, palaeopedological and sedimentological proxies, and it is confidently correlated with other loess records in the region (Roksolany and Kurortne), as well as with the marine isotope stratigraphy. The magnetic susceptibility records and palaeosol characteristics at Dolynske show an outstanding pattern that is transitional between eastern and south-eastern European loess records. Our data confirm that the well-developed S4 soil unit in Ukraine, and S5 units in Romania, Bulgaria and Serbia, correlate with the warm MIS 11. Furthermore, we suggest the correlation of rubified S6 palaeosols in Romania and Bulgaria and the V-S7-V-S8 double palaeosol in Serbia with S6 in Ukraine, a strong Mediterranean-type palaeosol which corresponds to MIS 15. Our new results do not support the hypothesis of a large magnetic lock-in depth like that previously interpreted for the Danube loess, and they prove that the Matuyama-Brunhes boundary is located within the palaeosol unit corresponding to MIS 19. The proposed stratigraphic correlation scheme may serve as a potential basis for further regional and global Pleistocene climatic reconstructions. [ABSTRACT FROM AUTHOR]

Heterogeneities in the magnetic signature along intraplate shear zones complicate their correlation with the physical processes that are involved in the geodynamic evolution of megathrusts. Isolating the preferred orientation of different magnetic minerals may provide insights into faulting processes, tectonics, and strain partitioning. Studies of exhumed analogs are fundamental to constrain variations in the magnetic properties with respect to a geodynamic context of intraplate shear zones. This study uses a combined statistical and magnetic approach to separate the contribution of coexisting petrofabrics to better interpret the heterogeneities in the magnetic signature. The main results indicate that there is a strong dependency among the variation in the magnetic properties and their anisotropy with the distance from the thrust faults and strain localization within the shear zone. Close to the main thrust, we observed a shear‐related fabric, indicating a high degree of non‐coaxial strain. Away from the thrust faults, the degree of anisotropy and the ellipsoids' oblateness gradually diminishes and subfabrics related to previous tectonic events or less intense deformation become dominant. Our observations also indicate strain decoupling across the basal thrust with dominant vertical uniaxial strain within the footwall. In contrast characterization of the anisotropy of magnetic remanence provides significant information on the variable response of different subpopulations of ferromagnetic minerals to shearing, indicating different degree of reworking or independent deformation processes. Plain Language Summary: Giant earthquakes commonly occur at active intraplate zones and to understand their formation and propagation, it is necessary to understand how rocks deform at intraplate shear zones. Variations in physical and rheological properties as well as fluids pressures are significant in controlling the seismicity. The directional variations of the magnetic properties of rocks strongly depends on these properties. This use of magnetic fabrics has been largely applied to convergent margins and mountain chains, but studies on intraplate shear zones that involve heterogeneous materials have been less studied. Our approach is to fully characterize the magnetic properties of rocks from intraplate shear zone and correlate these with geological processes related to the deformation. Key Points: Changes in the magnetic properties of fault rocks reveal the degree of tectonic reworking or structural position within the shear zoneAnisotropy of remanence experiments unravel distinct deformation stages or the heterogeneous response to the shearing by different grainsSystematic studies of exhumed analogs allow to constrain the magnetic properties in terms of localized versus distributed deformation [ABSTRACT FROM AUTHOR]

Based on analysis of gene structure of mamXY operon in Magnetospirillum gryphiswaldense strain MSR-1, we constructed a mamZ deletion mutant strain (ΔmamZ) and four complemented strains with different mamZ fragment lengths. Various cell phenotypic and physiological parameters were evaluated and compared among the wild-type (WT), mutant, and complemented strains. Cell growth rates were not notably different; however, magnetic response (Cmag) and iron uptake ability were significantly lower in ΔmamZ. High-resolution transmission electron microscopy (HR-TEM) showed that magnetosomes in ΔmamZ were small and irregular, and rock magnetic measurements suggested that they contained immature particles. In comparison to WT of MSR-1, intracellular iron content of ΔmamZ and the complemented strains cultured with 20 µmol/L iron source was similar or slightly higher. The complemented strains were unable to synthesize mature or normal amounts of magnetosomes, apparently because of abnormal expression of the transmembrane domain of MamZ protein. Real-time reverse transcription polymerase chain reaction (RT-qPCR) analysis showed that relative transcription levels of mamX and ftsZ-like genes in ΔmamZ were higher at 18 h than at 12 h, suggesting that MamXY proteins play cooperative functional roles in the magnetosome maturation process. Transcription level of mms6 was significantly upregulated in ΔmamZ (incubated at 12 h) and the complemented strains (incubated at 12 and 18 h), reflecting possible interaction between MamXY and Mms6 proteins during magnetosome biosynthesis. These findings, taken together, demonstrate the essential role of MamZ in the magnetosome maturation process in MSR-1. [ABSTRACT FROM AUTHOR]

Magnetotactic bacteria (MTB) intact cells have been applied in magnetic hyperthermia therapy of tumor, showing great efficiency in heating for tumor cell inhibition. However, the detailed magnetic hyperthermia properties and optimum heat production conditions of MTB cells are still poorly understood due to lack of standard measuring equipment. The specific absorption rate (SAR) of MTB cells is often measured by home-made equipment at a limited frequency and magnetic field amplitude. In this study, we have used a commercial standard system to implement a comprehensive study of the hyperthermic response of Magnetospirillum gryphiswaldense MSR-1 strain under 7 frequencies of 144–764 kHz, and 8 field amplitudes between 10 and 45 kA/m. The measurement results prove that the SAR of MTB cells increases with magnetic field frequency and amplitude within a certain range. In combination with the magnetic measurements, it is determined that the magnetic hyperthermia mechanism of MTB mainly follows the principle of hysteresis loss, and the heat efficiency of MTB cells in alternating magnetic field are mainly aff ected by three parameters of hysteresis loop, saturation magnetisation, saturation remanent magnetisation, and coercivity. Thus when we culture MTB in LA-2 medium containing sodium nitrate as source of nitrogen, the SAR of MTBLA-2 cells with magnetosomes arranged in chains can be as high as 4 925.6 W/g (in this work, all SARs are calculated with iron mass) under 764 kHz and 30 kA/m, which is 7.5 times than current commercial magnetic particles within similar size range. [ABSTRACT FROM AUTHOR]

Although a large number of magnetic declination and inclination measurements are available for the historical period from 1400 to 1900 CE, even the evolution of the axial dipole moment, the most prominent quantity of the geomagnetic field, is highly disputed for this time interval. Here, a new iterative Bayesian spherical harmonic model is constructed that combines historical (direct) and archeomagnetic or volcanic (indirect) records to better constrain the geomagnetic field evolution over this historical epoch. The resulting geomagnetic field reconstruction (BIGMUDIh.1) benefits from recently published and revised data for critical periods and regions. The highly variable data uncertainties and qualities are tackled with a weighting and selection scheme. Model uncertainties are mainly controlled by selection criteria applied to indirect intensity records and are estimated using a bootstrapping approach. A major improvement with respect to the established historical model gufm1 consists in the incorporation of archeointensities, which enables a direct estimation of the axial dipole evolution prior to 1840 CE. BIGMUDIh.1 yields a ∼2 µT (6%) decrease of the axial dipole component between 1500 and 1600 CE, followed by a relatively stable period until 1900 CE. Modeled declinations agree well with historical records and the gufm1 model derived from such records. Furthermore, the evolution of the South Atlantic Anomaly, driven by reverse flux patches (RFPs) at the core‐mantle boundary, is outlined. Periods of accelerated movement of the northern magnetic dip pole appear to be connected to the formation and changes of RFPs in the Northern Hemisphere. Plain Language Summary: The geomagnetic field, generated in the Earth's outer core, is our primary shield against energetic cosmic particles, thus protecting living organisms and human infrastructures. The Earth's magnetic field has been systematically monitored during the last ∼180 years, by a growing network of ground‐based observatories, which has been complemented by satellite recordings during the last decades. These measurements revealed significant changes in the strength and directions of the geomagnetic field. A decrease of the global field (axial dipole) strength of ∼7% has been determined since 1900 CE. This decline can be compared to more ancient geomagnetic variations derived from additional data sources. Man‐made observations of the Earth's magnetic field date back to the 15th century and mainly provide information on the angle between the geographic and magnetic North direction (declination) derived from compass measurements for navigation purposes. Knowledge about the field strength prior to first man‐made absolute intensity measurements in the 1830s can be gained from the laboratory analysis of rocks and archeological artifacts, which preserve the geomagnetic field over geological timescales. A combination of these different record types yields a decrease in the axial dipole strength of 6% during the 16th century followed by a nearly constant plateau until 1900 CE. Key Points: Development of a new geomagnetic field model for the historical period from 1400 to 1900 CEThe model evaluates and incorporates instrumental measurements and high‐quality archeointensity data and bootstraps lower quality dataAxial dipole intensity decreases between 1500 and 1600 CE and remains nearly constant between 1600 and 1900 CE [ABSTRACT FROM AUTHOR]

Recent paleomagnetic studies have shown that important short‐lived intensity fluctuations occurred during the first millennium BCE. However, the knowledge of the spatial and temporal extension of these features is still limited by the scarce availability of robust data. In this study we focus on the study of the intensity decrease that took place in Central Asia during the second half of the 1st millennium BCE after the high intensities that characterized the Levantine Iron Age Anomaly. Since previous archeointensities available for this period and region were obtained without accomplishing modern standards of quality, we present here new archeointensities that are derived from classical Thellier and Thellier experiments, including partial thermoremanent magnetization (pTRM) checks, thermoremanent magnetization (TRM) anisotropy and cooling rate corrections at the specimen level. The new 51 archeointensities, together with previous archeointensities, have been used to present a new local paleosecular variation curve for Central Asia. The results confirm the existence of an important geomagnetic field intensity decrease in South Uzbekistan from the 4th century BCE to the end of the 1st century BCE associated with rates of changes up to −15 μT/century. A critical analysis of the archeointensity global database indicates that this feature was present at continental scale, from Western Europe to Central Asia. However, this trend is not identified in other regions such as Japan or Mexico. Finally, the comparison with the dipole moment derived from recent global geomagnetic field reconstructions suggests a strong influence of non‐dipolar sources upon this continental intensity feature. Plain Language Summary: The Earth's magnetic field (also called the geomagnetic field) is continuously changing over time and space. Since the 19th century, the behavior of the geomagnetic field is known through direct observations performed in geomagnetic observatories and satellites. However, the only way to recover past geomagnetic field in ancient times is through paleomagnetic and archeomagnetic studies. In particular, archeomagnetism is the study of heated archeological materials, which include ferromagnetic particles acting as a compass and recording the geomagnetic field direction and strength at a certain time. When the archeological material cools down the ferromagnetic particles save the direction and intensity, like a photograph of the ancient geomagnetic field. Nowadays, there are very few archeomagnetic studies dealing with archeological materials from Central Asia. In this work, we present the variation of the geomagnetic field intensity between 600 BCE–600 CE in Uzbekistan deduced from a complete archeomagnetic investigation of 70 pottery fragments. The results confirm a rapid variation of geomagnetic field strength between 400 BCE and 100 BCE–1CE. To determine the spatial expression of this feature, we compared the obtained trend for Central Asia with the geomagnetic field intensity evolution in other regions of the world. Key Points: We present 51 new thermoremanent magnetization‐anisotropy corrected archeointensities for South UzbekistanAn important decrease in intensity is observed between 400 BCE and 100 BCE–1 CE, probably associated with non‐dipolar sourcesSimilar intensity V‐shaped trends are observed at continental scale [ABSTRACT FROM AUTHOR]

A GEOMAR (Kiel, Germany) research team has developed a passive electric field acquisition system for Autonomous Underwater Vehicles (AUVs) to optimize seafloor massive sulfides exploration. This sensor was made of two perpendicular and horizontal pairs of electrodes, and was successfully tested over active basalt‐hosted hydrothermal site TAG (26°N, Mid‐Atlantic Ridge) and several inactive sites in its vicinity. The resulting data underline the efficiency of combining deep‐sea electric and magnetic measurements for searching for active and inactive hydrothermal vent fields. With these datasets, it becomes possible to determine the geological nature of the targets and to constrain the characteristics of fluid circulation at depth without involving costly and invasive underwater tools such as Remotely Operated Vehicles or even manned submersibles to collect samples. Data analysis also revealed that AUV attitude variations induce distortions of the electric signal. These distortions start prevailing for dives at altitudes higher than 90 m above the seafloor, as the distance between the AUV becomes too important to guarantee that the signal produced by the geological target still dominates. To improve the acquisition system and reduce the overall noise, we discuss solutions that limit the impact of such attitude variations. These solutions consist of minor adjustments, such as masts at AUVs stern to tow damping electrodes arrays. In such configurations, we believe that deep‐sea passive electric measurements combined with high‐resolution magnetic measurements can become a highly efficient seafloor exploration tool, including for sulfide deposits associated with inactive hydrothermal systems. Plain Language Summary: Since the 1970s, the scientific community knows that the seafloor in the vicinity of mid‐ocean ridges is associated with hydrothermalism. Fluid circulations drain minerals from the deep crust that are precipitated near the seafloor. These minerals may form seafloor massive sulfide deposits that have raised the interest of the scientific community. Whereas active hydrothermal vent fields may be detected from surface vessels thanks to their associated chemical anomaly diffusing, and potentially drifting in the water column, inactive sites are more challenging to identify. High‐resolution magnetic data collected by deep‐sea exploration vehicles have proven their efficiency to undertake such exploration. Nevertheless, these data have limitations, such as the non‐uniqueness of the interpretations, and must be completed by others to optimize the efficiency of deep‐sea research. Here, we present a combined dataset made of deep‐sea passive electric, magnetic and bathymetric data, as well as water temperature analyzes collected simultaneously over several active and inactive basalt‐hosted hydrothermal sites of the Mid‐Atlantic Ridge. We emphasize the complementarity nature between high‐resolution passive electric and magnetic data to identify and study active and inactive hydrothermal sites, and propose engineering adjustments to ensure that this combination becomes the most efficient seafloor exploration tool in the future. Key Points: Basalt–hosted hydrothermal systems are associated with a strong electric signatureThis electric signature remains after the end of hydrothermal activityRedox processes between hydrothermal deposits and seawater are the dominant source of this signature [ABSTRACT FROM AUTHOR]

Our understanding of the past behavior of the geomagnetic field arises from magnetic signals stored in geological materials, e.g., (volcanic) rocks. Bulk rock samples, however, often contain magnetic grains that differ in chemistry, size, and shape; some of them record the Earth's magnetic field well, others are unreliable. The presence of a small amount of adverse behaved magnetic grains in a sample may already obscure important information on the past state of the geomagnetic field. Recently it was shown that it is possible to determine magnetizations of individual grains in a sample by combining X‐ray computed tomography and magnetic surface scanning measurements. Here we establish this new Micromagnetic Tomography (MMT) technique and make it suitable for use with different magnetic scanning techniques, and for both synthetic and natural samples. We acquired reliable magnetic directions by selecting subsets of grains in a synthetic sample, and we obtained rock‐magnetic information of individual grains in a volcanic sample. This illustrates that MMT opens up entirely new venues of paleomagnetic and rock‐magnetic research. MMT's unique ability to determine the magnetization of individual grains in a nondestructive way allows for a systematic analysis of how geological materials record and retain information on the past state of the Earth's magnetic field. Moreover, by interpreting only the contributions of known magnetically well‐behaved grains in a sample, MMT has the potential to unlock paleomagnetic information from even the most complex, crucial, or valuable recorders that current methods are unable to recover. Plain Language Summary: Our understanding of the past behavior of the Earth's magnetic field relies on our ability to interpret magnetic signals from rocks. Currently, we measure bulk samples consisting of many magnetic grains at once. Not all magnetic grains are good recorders of the geomagnetic field. The presence of even small amounts of adverse behaved grains in a sample already obscures vital information about the Earth's magnetic field. Here we present and establish a new method that determines magnetizations of individual grains in a sample: Micromagnetic Tomography. This new and exciting method allows to select and interpret only magnetizations of grains that are known good recorders in a sample. This will unlock magnetic information from even the most complex, crucial, or valuable samples that current methods are unable to recover. Key Points: Micromagnetic Tomography enables determining, selecting, and interpreting magnetizations of individual grains in a sampleWe obtained magnetic directions and rock‐magnetic information from subsets of grains in both a synthetic and a natural sampleMicromagnetic Tomography has the potential to unlock magnetic information from even the most complex recorders that currently goes obscured [ABSTRACT FROM AUTHOR]

Beginning in 1964, an academic lineage of Robert DuBois and his students, Daniel Wolfman and Jeffrey Eighmy, developed dedicated United States‐based archaeomagnetic research programs. Collectively, they analyzed over 5,377 archaeomagnetic sites, primarily from North America, dated to less than 2,000 years old. Yet despite their decades of effort, few journal publications resulted. Most of their published results are embedded in archeological reports, often without technical data, which limits the data's accessibility. Furthermore, when published, the results are generally averaged at the site level using statistical conventions different from today's standards, limiting the data's comparability and (re)usability. In 2015, we undertook a salvage archival study to digitize the surviving data and metadata from the scientists' individual estates and emeritus collections. We digitized measurement data from more than 51,000 specimens, reinterpreted them using modern conventions, and uploaded them to the FAIR‐adhering magnetic data repository, earthref.org/MagIC. The reinterpreted site‐level results from the three laboratories are mutually consistent, permitting the individual data sets to be combined and analyzed as single regional entities. Through incorporation into the MagIC repository, these legacy data are now accessible for incorporation into archaeomagnetic and global magnetic field modeling efforts, critical to understanding Earth's magnetic field variation through time. In the Four Corners region of the United States Southwest, this digitized archive advances the development of a new regional paleosecular variation curve used in archaeomagnetic dating. This project highlights both the value and complexities of managing legacy data; the many lessons learned to set a precedent for future paleomagnetic data recovery efforts. Plain Language Summary: Archaeomagnetism is the study of Earth's past magnetic field through researching the magnetic signatures retained in well‐dated archeological materials. The most commonly studied materials are those that have experienced high temperatures due to human‐made fires. Due to humans' global occupation, there is a potential for globally distributed archaeomagnetic sampling, which is essential for high‐resolution global magnetic field models. However, there is considerable variation in the documentation and accessibility of data from certain regions, including North America. In 2015, a salvage archival project was initiated to recover the life's work of three North American archaeomagnetists. The effort resulted in the digitization and formatting of the data within DuBois' and Wolfman's estates, and Eighmy's archive. In total, measurement data from more than 51,000 specimens, from 5,377 archeological features, were processed and uploaded to a centralized online data repository, MagIC. This repository ensures that the data, representing 130 person‐years of work, are now findable and accessible, permitting the data to be re‐used in future modeling projects. One such application for these data is the development of a new regional model for the Four Corners region of the United States Southwest that traces the location of the magnetic north pole through time. Key Points: We digitized 6 decades of legacy archaeodirectional measurements from three archives (>51k specimens), adding them to a FAIR repository, MagICThe site‐level results (reanalyzed using modern statistical conventions) are consistent between the archivesThe majority of the data have site provenance in North America and are dated to less than 2,000 years old [ABSTRACT FROM AUTHOR]

Silicate‐hosted magnetic inclusions are a widespread fine grained magnetic component in marine sediments. However, their paleomagnetic and paleoenvironmental significance remains elusive as they are often overshadowed by unprotected detrital and biogenic magnetic components. We developed a protocol to extract silicate inclusions from sediments sampled from the central Pacific and the Okhotsk Sea. Our results show that the threshold condition (hydrochloric acid 10 mol/L with a reaction time of 24 h) can efficiently remove biogenic and unprotected magnetic phases and preserve silicate hosted magnetic inclusions that manifest a wide coercivity spectrum ranging between 10 and 300 mT with a median coercivity of ∼100 mT based on systematic rock magnetic analyses. This approach was applied to the Okhotsk Sea sediments, whose magnetic phases are dominantly derived from surrounding volcanic formations, spanning the last interglacial period. The residues after dissolution present a similar temporal variation compared to the bulk magnetic signal despite significant drops in amplitude. This suggests that the preserved signals of silicate inclusions can qualitatively represent the volcanic component. We suggest that when applied to sediments with complex magnetic components, this approach has the potential to extract volcanic components for paleoenvironmental reconstructions. Plain Language Summary: Magnetic mineral inclusions within silicates are an important magnetic component in marine sediments that can record long‐term paleomagnetic and paleoenvironmental information. However, it remains difficult to quantify their contribution due to the mixed magnetic properties in marine sediments including biogenic and detrital magnetic minerals with diverse grain sizes. We carried out systematic magnetic measurements to trace the dissolution processes of magnetic particles in sediments from the central Pacific Ocean and Okhotsk Sea and found the conditions (hydrochloric acid 10 mol/L with 24 h reaction time) that can efficiently remove biogenic and detrital magnetite leaving silicates that host magnetic inclusions. The preserved signals of silicate inclusions can qualitatively represent the volcanic component in marine sediments. We apply this approach to the central Okhotsk Sea sediments spanning the last interglacial period to demonstrate its potential for paleoenvironment reconstruction. Key Points: Dissolution behavior of unprotected magnetic particles follows the sequence from superparamagnetic particles, finer grains, and to coarser grainsMagnetic inclusions within silicates are characterized of broad coercivity distribution of 10–300 mTMagnetic residues after dissolution contain dominantly volcanic components in marine environment [ABSTRACT FROM AUTHOR]

Diagenesis can have a major impact on sedimentary mineralogy. Primary magnetic mineral assemblages can be modified significantly by dissolution or by formation of new magnetic minerals during early or late diagenesis. At International Ocean Discovery Program Site C0023, which was drilled in the protothrust zone of the Nankai Trough during Expedition 370, offshore of Shikoku Island, Japan, non‐steady state conditions have produced a complex sequence of magnetic overprints. Detailed rock magnetic measurements, which characterize magnetic mineral assemblages in terms of abundance, grain size, and composition, were conducted to assess magnetic mineral alteration and diagenetic overprinting. Four magnetic zones (MZs) are identified down‐core from ∼200 to 1,100 m below sea floor based on rock magnetic variations. MZ 1 is a high magnetic intensity zone that contains ferrimagnetic greigite, which formed at shallow depths and is preserved because of rapid sedimentation. MZs 2 and 4 are low magnetic intensity zones with fewer magnetic minerals, mainly coarse‐grained (titano‐)magnetite and hematite. This magnetic mineral assemblage is a remnant of a more complex assemblage that was altered diagenetically a few million years after deposition when the site entered the Nankai Trough. MZ 3 is a high magnetic intensity zone between MZs 2 and 4. It contains authigenic single‐domain magnetic particles that probably formed from fluids that circulated through faults in the accretionary prism. Varying sediment supply and organic matter input through time, burial temperature, and tectonic fluid circulation are the primary drivers of magnetic mineral assemblage variations. Key Points: Four down‐core diagenetic zones are identified with magnetic mineral assemblages reflecting sediment provenance and diagenetic processesLimited exposure of sediments to dissolved sulfide due to rapid burial leads to greigite preservation in the upper ∼460 mHigh‐temperature diagenetic processes are responsible for later iron oxide formation and reduction in deeper sediments [ABSTRACT FROM AUTHOR]

The Colorado Plateau Coring Project Phase 1 (CPCP‐1) acquired three continuous drill cores from Petrified Forest National Park (PFNP), Arizona, U.S.A., two of which (CPCP‐PFNP13‐1A and CPCP‐PFNP13‐2B) intersected the Upper Triassic Chinle Formation, Lower(?)‐Middle Triassic Moenkopi Formation (MF) and Permian Coconino Sandstone. We examined both cores to construct a high‐resolution magnetostratigraphy of MF strata, and progressive demagnetization data yield well‐defined, interpretable paleomagnetic results. Each lithostratigraphic member of the MF (Wupatki, Moqui, and Holbrook members) contains authigenic and detrital hematite as the dominant magnetic carrier with distinguishing rock magnetic characteristics. Magnetostratigraphy of MF strata in both CPCP‐1 cores consists of six normal and six reverse polarity magnetozones, from the youngest to the oldest, MF1n to MF6r. Recent single‐crystal chemical abrasion–thermal ionization mass spectrometry (CA‐TIMS) U‐Pb data from a sample in magnetozone MF1n yield a latest Anisian/earliest Ladinian (241.38 ± 0.43 Ma) age. Correlation of the CA‐TIMS‐calibrated magnetostratigraphy with the astronomically tuned polarity timescale for the Middle Triassic deep‐marine Guandao (GD) section of South China ties the magnetozone MF1n with GD8 and MF6r with GD2r, and implies that the MF spans, at most, the earliest Anisian (Aegean) to latest Anisian (Illyrian)/earliest Ladinian stages (ca. 246.8 to 241.5 Ma). This age estimate for the MF suggests that the timespan of the regional, pre‐Norian disconformity is about 17 Ma, which demonstrates that MF vertebrate fossil assemblages in east‐central Arizona are millions of years (minimally 3–4 Ma) younger than previously suggested and are all Anisian in age, with no indications of substantial hiatuses in the MF section. Plain Language Summary: The Triassic Period, between about 252 and 201.5 million years ago, witnessed many significant Earth System events, including extreme temperature swings, high atmospheric carbon‐dioxide concentration, and biotic recovery from the Earth's greatest mass extinction at its beginning and another mass extinction at its end. This research is aimed at obtaining a high‐resolution magnetic polarity stratigraphy for the Moenkopi Formation based on two cores recovered from the Petrified Forest National Park, Arizona, U.S.A., to provide a robust age constraint of its constituent fossil assemblages that will allow a correlation across continents, document key biotic events, such as the recovery from the end‐Permian mass extinction, the diversification of reptiles, and the origin of dinosauromorphs. We have identified six magnetic reversal events during the deposition of the Moenkopi Formation rocks and suggest that these strata span, at most, ∼246.8 Ma to ∼241.5 Ma. This study also suggests that the time gap between the Moenkopi Formation and the overlying Chinle Formation, the home of the petrified forests, is about 17 Ma long. The revised age model of the Moenkopi Formation from this study will provide a high‐resolution age constraint for future paleoclimatic, biotic, and correlation studies of rocks from a similar age on a global basis. Key Points: Complete magnetostratigraphy of the entire Middle Triassic age Moenkopi Formation drilled at the Petrified Forest National Park, ArizonaA high sampling frequency provides a comparison with polarity records from surface exposures elsewhere in the Colorado PlateauRevised estimated age of the Moenkopi Formation (ca. 246.8 Ma–241.5 Ma) requires a reinterpretation of its constituent fossil assemblages [ABSTRACT FROM AUTHOR]

High‐quality paleointensity data are essential for improving our understanding of the geomagnetic field; however, it is challenging to find materials that reliably record full vector magnetization going back in time. Here, we examine a new candidate material for paleointensity studies: clinkers, which are rocks that have been baked, metamorphosed, or melted by underlying coal seam fires. Previous studies conducted on clinkers suggest that they may be high‐fidelity magnetic field recorders. However, due to the inhomogeneity of clinker deposits and limited scope of previous studies, it is unknown under what conditions these conclusions hold true. To better assess this, we quantified the variation of magnetic properties within clinker deposits collected from the Powder River Basin, Montana, as a function of lithology, oxidation state, distance from the coal seam, and location. Our results indicate that the clinker products contain three main magnetic minerals: magnetite, hematite, and the rare ε‐Fe2O3. Clinker lithology was found to be the primary control on magnetic mineralogy, where strongly baked sediment and porcellanite are dominated by varying proportions of hematite, ε‐Fe2O3, and magnetite, and paralavas are dominated by low‐Ti magnetite. All clinker materials are thermally stable and likely experienced temperatures in excess of the magnetite Curie temperature. Grain size analysis indicates that the magnetic particles in all clinker materials are amenable to high‐quality paleointensity study. In total, our study confirms that clinkers should be reliable full vector paleomagnetic recorders. Plain Language Summary: Measuring Earth's ancient magnetic field strength is challenging due to a paucity of reliable recorders. However, to understand how the geomagnetic field has behaved over time, robust records of field strength are necessary. Here, we examine clinkers, which are rocks that have been baked, metamorphosed, or welded by coal seam fires, as a potential new material for characterizing the ancient magnetic field strength. Prior study suggested that clinkers may be robust magnetic recorders. However, due to heterogeneity in clinker deposits, more extensive study is required to understand the extent of their suitability for paleomagnetic analysis. In our study, we quantified the variation of magnetic properties within clinker deposits collected from the Powder River Basin, Montana, as a function of clinker rock type, oxidation state, distance from the coal seam, and location. Our results show that clinkers contain three main magnetic minerals: magnetite, hematite, and the rare ε‐Fe2O3; the latter of which has so far only been found as a primary magnetic mineral in baked archeological artifacts. We found that clinker rock type is the primary control on magnetic mineralogy. Overall, the rock magnetic characteristics of clinkers suggest they should be reliable recorders of ancient magnetic field strength. Key Points: We examine clinkers, which are pyro‐metamorphic rocks formed by coal seam fires, as a new candidate material for paleointensity studiesWe find clinker products contain three main magnetic minerals: magnetite, hematite, and the rare ε‐Fe2O3Overall, our rock magnetic results suggests that clinkers should be reliable paleomagnetic full vector recorders [ABSTRACT FROM AUTHOR]

Isothermal remanent magnetization (IRM) curves are used widely in rock magnetic and environmental magnetic studies to characterize magnetic properties of natural samples. Previous theoretical and experimental investigations indicate that magnetostatic interactions can strongly affect the IRM behavior. In order to quantitatively investigate this effect, we modeled IRM curves and hysteresis properties for magnetite assemblages with variable morphologies (grain size, elongation, and shape) using the finite‐element micromagnetic modeling code MERRILL. We also conducted an analytical study of IRM behavior for noninteracting single domain grains utilizing the Stoner–Wohlfarth model. It is found that multiple Gaussian components do not necessarily reflect multiple magnetic mineral populations. For example, magnetostatic interactions can produce coercivity distributions that resemble results of some samples containing a detrital and extracellular (D + EX) and a biogenic soft or hard (BS/BH) coercivity components. Simulated IRM curves for different morphologies of interacting flattened grains are similar, indicating that the effect of interactions can overshadow the effect of grain morphologies. Moreover, our micromagnetic and analytical calculations consistently indicate that the IRM curves for noninteracting fine‐grained assemblages are mostly determined by grain shape (elongated or flattened) and elongation distributions of the magnetic mineral assemblages. Our simulations present possible outcome of IRM curves for magnetic mineral assemblages with controlled grain size, shape and microstructures, which provides important theoretical constraints on characterizing complex magnetic mineral components in natural samples through IRM curves and hysteresis. Plain Language Summary: Tiny magnetic mineral grains, often in the nanometer and micrometer size, in geological samples retain critical information about past environmental changes and geomagnetic field variations. Knowing the properties of magnetic minerals is crucial to decode magnetic mineral records. Decomposing isothermal remanent magnetization (IRM) curve into multiple magnetic mineral parts is a powerful technique, but is often complicated by the common presence of magnetic interactions where magnetic mineral grains are clumped to each other. This process is similar to attracting and repelling of magnets, but occurs at very small, microscopic scale. Here we have applied computer‐modeling to calculate how neighboring magnetic grains affect the IRM curves. Our simulation results provide new physical constraints on analyzing IRM data, which is important to make robust environmental and geophysical interpretations. Key Points: Micromagnetic calculations elucidate potential origin of multiple Gaussian remanent coercivity componentsThe elongation distribution and grain morphologies strongly affect the shape of IRM curves for noninteracting fine‐grained particlesMagnetostatic interactions can overshadow the effect of grain morphologies and can also cause multiple Gaussian coercivity components [ABSTRACT FROM AUTHOR]

Magnetotactic bacteria (MTB) belong to several phyla. This class of microorganisms exhibits the ability of magneto-aerotaxis. MTB synthesize biominerals in organelle-like structures called magnetosomes, which contain single-domain crystals of magnetite (Fe3O4) or greigite (Fe3S4) characterized by a high degree of structural and compositional perfection. Magnetosomes from dead MTB could be preserved in sediments (called fossil magnetosomes or magnetofossils). Under certain conditions, magnetofossils are capable of retaining their remanence for millions of years. This accounts for the growing interest in MTB and magnetofossils in paleo- and rock magnetism and in a wider field of biogeoscience. At the same time, high biocompatibility of magnetosomes makes possible their potential use in biomedical applications, including magnetic resonance imaging, hyperthermia, magnetically guided drug delivery, and immunomagnetic analysis. In this review, we attempt to summarize the current state of the art in the field of MTB research and applications. [ABSTRACT FROM AUTHOR]

The martian dynamo's strength and duration are essential for understanding Mars' habitability and deep interior dynamics. Although most northern volcanic terranes were likely emplaced after the martian dynamo ceased, recent data from the InSight mission show stronger than predicted crustal fields. Studying young volcanic martian meteorites offers a precise, complementary method to characterize the strength of the martian crustal field and examine its implications for past dynamo activity. We present the first rock and paleomagnetic study of nine mutually oriented samples from the martian Nakhlite meteorite Miller Range (MIL) 03346, which is well‐suited for paleomagnetic analysis due to its well‐known age (1,368 ± 83 Ma) and lack of significant aqueous, thermal, and shock overprinting. Rock magnetic analysis, including quantum diamond microscope imaging, showed that the natural remanent magnetization (NRM) is carried by Ti‐magnetite crystals containing µm‐scale ilmenite exsolution lamellae, which can accurately record ancient magnetic fields. Demagnetization of the NRM revealed a high coercivity magnetization interpreted to date from the age of eruption based on its intensity, unidirectionality, and a passing fusion crust baked contact test. Paleointensities of four samples reveal a 5.1 ± 1.5 µT paleofield, representing the most reliable martian paleointensity estimates to‐date and stronger than the 2 µT surface fields measured by InSight. Modeling shows that the observed fields can be explained by an older subsurface magnetized layer without a late, active dynamo and support a deeply buried, highly magnetized crust in the northern hemisphere of Mars. These results provide corroborating evidence for strong, small‐scale crustal fields on Mars. Plain Language Summary: Mars used to have a magnetic field. So far, we do not know the exact time when the dynamo creating this field stopped. The southern hemisphere of Mars is strongly magnetic, while the northern half is not. Our best guess is that the dynamo decayed about 4 billion years ago from the strength of these surface fields. However, new data from the InSight mission on Mars show that the northern crust may be more magnetic than previously thought. This finding could mean that the martian dynamo has existed in a weakened state for an extended period. Here we are looking at the magnetic properties of the martian nakhlite meteorite Miller Range (MIL) 03346. Using the novel quantum diamond microscope and classical rock—and paleomagnetic techniques, we show that MIL can record and retain information on the martian field from when the rock formed 1.4 billion years ago. We show that the strength of the field recorded by MIL is an order of magnitude stronger than what current satellite models predict. Our computer models of the decay of magnetic fields predict that a late weak martian dynamo is not needed to explain the strong magnetic signature of MIL. Key Points: Miller Range 03346 shows paleointensities an order of magnitude stronger than expected from their age and satellite models of the likely source regionModeling indicates thermal remanences assist the propagation of magnetic fields of subsurface source layers to the surfaceMagnetic fields on the surface of Mars are likely heterogeneous at length scales <200 km and stronger than previously thought [ABSTRACT FROM AUTHOR]

For archeomagnetic dating, high‐quality directional and intensity paleosecular variation curves are needed. The Azores Archipelago in the mid‐Atlantic Ocean provides a wealth of volcanic products erupted during the Holocene, making it an ideal location to (1) gather paleomagnetic data from well dated lava flows and (2) construct a paleosecular variation (PSV) curve that enables paleomagnetic dating of volcanic products with unknown age. Here, we present new full‐vector paleomagnetic data from Pico Island, and combine the new data with existing data from neighboring islands to construct a new full‐vector PSV curve for the Azores Archipelago. An extensive rock‐magnetic study underpins the quality of our paleomagnetic carriers. From Pico Island, we obtained 21 new mean site directions; and 15 paleointensity estimates with the multimethod paleointensity approach from 12 sites, the age was known for 14 and 10 sites, respectively. By bootstrapping the non‐Gaussian uncertainty estimates of the radiocarbon age calibrations and the confidence intervals associated with the direction and paleointensity estimates, we produce the first full‐vector PSV curve with confidence intervals for the Azores covering the past 2 kyr. The PSV curve reveals a period of low inclination between ∼900 and 1560 AD, with minimum values of 32°. The potential of our new full‐vector PSV curve is demonstrated by successfully dating five lava flows from Pico Island. Plain Language Summary: The Earth's magnetic field is highly variable over time and space. Lava flows archive the geomagnetic field upon emplacement and thereby forming an archive of geomagnetic field changes. The Azores Archipelago is located in the mid‐North Atlantic Ocean providing a unique location to study the changes of the Earth's magnetic field. Here, we present new paleomagnetic data from Pico Island, Azores. We combine the newly derived data with available data from neighboring islands and compose a curve of the changes, for both the direction and the strength of the Earth's magnetic field over the past 2,000 years. Key Points: New paleomagnetic data from Pico Island in the mid‐North Atlantic regionData reveals an inclination low with minimum values of 32° from 900 to 1560 ADWe present the first full‐vector paleosecular variation curve for the Azores covering the past 2 kyr, suitable for paleomagnetic dating [ABSTRACT FROM AUTHOR]

As iron-bearing minerals--ferrimagnetic minerals in particular--are sensitive to stress, temperature, and presence of fluids in fault zones, their magnetic properties provide valuable insights into physical and chemical processes affecting fault rocks. Here, we review the advances made in magnetic studies of fault rocks in the past three decades. We provide a synthesis of the mechanisms that account for the magnetic changes in fault rocks and insights gained from magnetic research. We also integrate nonmagnetic approaches in the evaluation of the magnetic properties of fault rocks. Magnetic analysis unveils microscopic processes operating in the fault zones such as frictional heating, energy dissipation, and fluid percolation that are otherwise difficult to constrain. This makes magnetic properties suited as a "strain indicator," a "geothermometer," and a "fluid tracer" in fault zones. However, a full understanding of faulting-induced magnetic changes has not been accomplished yet. Future research should focus on detailed magnetic property analysis of fault zones including magnetic microscanning and magnetic fabric analysis. To calibrate the observations on natural fault zones, laboratory experiments should be carried out that enable to extract the exact physicochemical conditions that led to a certain magnetic signature. Potential avenues could include (1) magnetic investigations on natural and synthetic fault rocks after friction experiments, (2) laboratory simulation of fault fluid percolation, (3) paleomagnetic analysis of postkinematic remanence components associated with faulting processes, and (4) synergy of interdisciplinary approaches in mineral-magnetic studies. This would help to place our understanding of the microphysics of faulting on a much stronger footing. Plain Language Summary The Earth's surface is riddled with faults that largely contribute to landscape evolution and human activities. Some of these faults produce earthquakes of different magnitudes including some with catastrophic consequences. Understanding faulting mechanisms benefits society when predictions about rupture are made. Fault zones preserve an excellent record of chemical and physical processes involved in failure. Among other analytical methods, magnetic studies prove to be an emergent and untapped source of information on these processes. These methods, focused on prefaulting, synfaulting, and postfaulting mineral changes, have resulted in significant advances in our understanding of the conditions of faulting. In this review, we present an extensive account of the state of knowledge and highlight current challenges and future avenues of fault magnetism research. [ABSTRACT FROM AUTHOR]

Archeological materials from the most ancient open‐pit gold mine in Europe have been investigated using mineral magnetic methods as part of the multidisciplinary research of the site. The aim of the study was to employ rock‐magnetic characteristics (magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization and various magnetic grain‐size dependent ratios) for classification of a collection of 177 samples, taken from Late Bronze age waste heaps, pristine rocks, natural soils and soils from cultural layers. Factor analysis and k‐means cluster analysis revealed that four clusters explain the best mineral magnetic data. Results from the thermomagnetic analysis and thermal demagnetization of composite isothermal remanence proved that the main magnetic minerals in the collection are magnetite/maghemite, hematite, and goethite. Based on the magnetic properties, samples from clusters 1 and 3 were identified as influenced by fire—archeological structures and waste heaps with the use of fire setting, respectively. Samples belonging to cluster 2 were dominated by goethite and hematite, thus identified as rock residues. Materials grouped in cluster 4 showed magnetic characteristics typical of natural soils and were thus related to this class of materials. The obtained clustering of the samples agreed well with their archeological assignment. Spatial distribution of cluster members across the site provides valuable environmental information for the location of the mining activities, their lateral spread and the technology used. It was concluded that magnetic mineral analysis is a precise, sensitive, and a highly effective method for characterization and classification of materials from ancient mining. Key Points: Archeological materials from ancient gold mining site Ada Tepe are studied by rock magnetismFactor and cluster analyses classify the materials in four clusters—fired soil, host rocks, mining waste with use of fire, and natural soilsAncient gold mining with the use of fire‐setting is clearly discriminated using rock magnetic parameters [ABSTRACT FROM AUTHOR]

Inverse magnetic fabrics defined by anisotropy of magnetic susceptibility with the longest principal axis perpendicular to bedding were identified in the studied samples of Ordovician sedimentary rocks from the Barrandian area, Czech Republic. These fabrics are related to ankerite fibers in association with cone‐in‐cone structures. To understand the meaning of such inverse magnetic fabrics for geological interpretations, a new, more detailed classification of inverse magnetic fabrics' types is formulated in this paper. Distinguishing the structural (i.e., shape) and magnetocrystalline anisotropies in rocks, three new (sub)types of magnetic fabrics were defined in this study based on the combination of structural normal/inverse and magnetocrystalline normal/inverse anisotropies. As a result, normal magnetic fabric is extended by new fabric types associated with inverse anisotropy: simple inverse, pure inverse, and pseudo‐normal magnetic fabrics. The studied fibrous ankerite shows simple inverse magnetic fabric, which results from the combination of normal magnetocrystalline and inverse structural anisotropies. Key Points: Two kinds of normal and inverse rock anisotropies, that is, magnetocrystalline and structural, result in four magnetic fabric typesBesides normal fabric, there are two types of inverse fabric (simple and pure) and one "double inverse," named here as a pseudo‐normalStudied ankerite shows a simple inverse magnetic fabric as a combination of normal magnetocrystalline and inverse structural anisotropies [ABSTRACT FROM AUTHOR]

The Early Mesozoic is a key period for the formation of the Asia continent. In this study, in order to reconstruct the Early Mesozoic paleogeography of Proto‐Asia, we carried out a paleomagnetic study on the Early Triassic strata from the Chengde Basin in the northeastern North China Craton (NCC). Rock magnetic investigations reveal magnetite and hematite as the main magnetic carriers. Characteristic remanent magnetization directions from 21 sites show normal and reversed polarities and site‐mean directions pass fold tests. After inclination shallowing (IS) correction with the elongation/inclination method, a mean direction is calculated at Ds/Is = 322.5°/39.5° (ks = 32.6, α95s = 5.7°) in stratigraphic coordinates. The corresponding Early Triassic paleomagnetic pole (λ/φ = 53.5°N/9.5°E, A95 = 5.3°) overlaps with coeval poles that have also been corrected for IS reported from the western part of the NCC. This result indicates that there is no relative movement between the eastern and western parts of the NCC. With all IS‐corrected paleomagnetic poles, a mean Early Triassic pole is recalculated for the NCC at λ/φ = 59.4°N/13.4°E (A95 = 4.7°). We use this pole to reconstruct the paleogeography of Proto‐Asia and confirm previous studies that did not use IS corrections, in which two "triangle bay‐shaped" oceans, the Paleo‐Tethys Ocean and the Mongol‐Okhotsk Ocean, existed along the southern and northern margins of the unified NCC‐Mongolian Block (MOB). Clockwise rotations of the South China Craton and Siberia Craton relative to the NCC‐MOB during the Early Mesozoic led to the final closure of both oceans. Key Points: Early Triassic red beds in the Chengde Basin of the northeastern NCC experienced severe inclination shallowingAn inclination shallowing‐corrected Early Triassic paleomagnetic pole is reported from northeastern NCCA modified Early Triassic paleogeography of Asian blocks is reconstructed [ABSTRACT FROM AUTHOR]

First‐order reversal curve (FORC) distributions are a powerful diagnostic tool for characterizing and quantifying magnetization processes in fine magnetic particle systems. Estimation of FORC distributions requires the computation of the second‐order mixed derivative of noisy magnetic hysteresis data. This operation amplifies measurement noise, and for weakly magnetic systems, it can compromise estimation of a FORC distribution. Previous processing schemes, which are based typically on local polynomial regression, have been developed to smooth FORC data to suppress detrimental noise. Importantly, the smoothed FORC distribution needs to be consistent with the measurement data from which it was estimated. This can be a challenging task even for expert users, who must adjust subjectively parameters that define the form and extent of smoothing until a "satisfactory" FORC distribution is obtained. For nonexpert users, estimation of FORC distributions using inappropriate smoothing parameters can produce distorted results corrupted by processing artifacts, which can lead to spurious inferences concerning the magnetic system under investigation. We have developed a statistical machine learning framework based on a probabilistic model comparison to guide the estimation of FORC distributions. An intuitive approach is presented that reveals regions of a FORC distribution that may have been smoothed inappropriately. An associated metric can also be used to compare data preparation and local regression schemes to assess their suitability for processing a given FORC data set. Ultimately, our approach selects FORC smoothing parameters in a probabilistic fashion, which automates the derivative estimation process regardless of user expertise. Key Points: We develop a probabilistic framework for estimating FORC distributionsUsing Bayesian model selection, we identify underfitting and overfitting of FORC distributionsFORCsensei software can be used to determine smoothing parameters to estimate a FORC distribution [ABSTRACT FROM AUTHOR]

Magnetic parameters are used extensively to interpret magnetic mineral assemblage variations in environmental studies. Conventional room temperature measurements of bulk magnetic parameters, like the anhysteretic remanent magnetization (ARM) and the ratio of the susceptibility of ARM to magnetic susceptibility (χ), can reflect, respectively, magnetic mineral concentration and/or particle size variations in sediments, although they are not necessarily well suited for identifying magnetic components within individual magnetic mineral assemblages. More advanced techniques, such as first‐order reversal curve (FORC) diagrams and low‐temperature (LT) magnetic measurements, can enable detailed discrimination of magnetic assemblages. Here, we integrate conventional bulk magnetic measurements alongside FORC diagrams, LT measurements, and X‐ray fluorescence core‐scan data, transmission electron microscope observations, and principal component analysis of FORC diagrams to identify and quantify magnetic mineral assemblages in eastern Mediterranean sediments. The studied sediments were selected because they contain complexly varying mixtures of detrital, biogenic, and diagenetically altered magnetic mineral assemblages that were deposited under varying oxic (organic‐poor marls) to anoxic (organic‐rich sapropels) conditions. Conventional bulk magnetic parameters provide continuous records of environmental magnetic variations, while more time‐consuming LT and FORC measurements on selected samples provide direct ground‐truthing of mineral magnetic assemblages that enables calculation of magnetization contributions of different end members. Thus, a combination of conventional bulk parameters and advanced magnetic techniques can provide detailed records from which the meaning of environmental magnetic signals can be unlocked. Key Points: We present an assessment of bulk and component‐specific magnetic measurements for sediments deposited under variable redox conditionsBulk magnetic parameters provide valuable delineation of continuous environmental variationsComponent‐specific techniques enable quantification of individual magnetic mineral assemblages to understand environmental variations [ABSTRACT FROM AUTHOR]

Red beds are important targets for paleomagnetic studies, yet discriminating secondary chemical remanent magnetization (CRM) from primary depositional remanent magnetization (DRM) in them remains challenging. Here we reanalyze the thermal demagnetization data of and conduct comprehensive rock magnetic, Mössbauer spectroscopic and petrographic studies on red beds from four Cenozoic basins on the eastern Tibetan Plateau (China): the Gongjue, Nangqian, Shanglaxiu, and Jinggu basins. The red beds in the latter two basins are remagnetized, as are most Nangqian red beds. The Gongjue red beds and some Nangqian red beds retain a DRM. Our results reveal that detrital (titano)magnetite and hematite are well preserved in red beds retaining the DRM, whereas remagnetized red beds contain large amounts of authigenic hematite and goethite with detrital Fe‐bearing minerals strongly altered. Postdepositional diagenetic alteration induced by heating and/or fluid circulation related to magmatism and/or crustal deformation is probably the main reason for the remagnetization. Hematite carrying the CRM in remagnetized red beds has wide distribution of grain size and unblocking temperature spectra, while hematite carrying the DRM is usually coarse and has confined unblocking temperature spectrum. This can be used as a criterion for diagnosing remagnetization. Nanoscale goethite appears to occur only in remagnetized red beds: another sensitive criterion for discriminating CRM from DRM. These property‐based criteria constrain the origin of the NRM in red beds better than the classic paleomagnetic field tests. Our research emphasizes that integrated rock magnetic, Mössbauer spectroscopic and petrographic studies provide robust tools to diagnose remagnetization in red beds. Key Points: Remagnetized red beds contain large amounts of fine‐grained authigenic hematite and goethiteDiagenetic alteration induced by heating and/or fluid circulation is probably the main reason for the remagnetization in red bedsThermomagnetic behavior and appearance of goethite are two reliable criteria for diagnosing remagnetization in red beds [ABSTRACT FROM AUTHOR]

Gyro‐remanent magnetization (GRM) is a frequently occurring yet unwanted remanence contamination for certain samples during alternating field (AF) demagnetization of the natural remanent magnetization. The origin and detailed properties of GRM have not yet been fully understood. In this study, systematic rock magnetic analyses were conducted on marine greigite‐bearing samples of Hole U1433A drilled by the IODP Expedition 349 from the South China Sea. Results show that GRM is mostly acquired above ~55 mT AF demagnetization and can be effectively removed by heating to ~400°C during thermal demagnetization but a secondary tail could remain until ~585°C. In addition, no apparent GRM was observed during the AF demagnetization for the 400°C thermally treated samples. These results strongly suggest that GRM is dominantly carried by single domain (SD) greigite but with minor contributions from SD magnetite. Thus, thermal treatment alone or the hybrid demagnetization (i.e., thermal demagnetization at ~400°C first then systematical AF demagnetization) can efficiently avoid the GRM acquisition and be beneficial for relative paleointensity estimation for greigite‐bearing samples. Besides, GRM carried by greigite has a low thermal stability. Our results also show AF demagnetization spectra of anhysteretic remanent magnetization (ARM) could be strongly distorted by GRM effects due to both have a preference of SD particles. Thus, the median destructive field of ARM is improper to be used as a coercivity proxy for greigite‐bearing samples. Instead, the biplot analysis of AF demagnetization of natural remanent magnetization and ARM can be used to evaluate the relative content of greigite. Key Points: Both greigite and the coexistent magnetite can acquire a GRM during the AF demagnetizationMagnetite lost the ability to acquire a GRM when greigite is disintegrating after first being heated to 400°CGRM can be used as a proxy for semiquantification of greigite concentration [ABSTRACT FROM AUTHOR]

The important role played by the upper plate in convergence zones dynamics has long been underestimated but is now more and more emphasized. However, the influence of its thickness and/or strength on orogenic systems evolution remains largely unknown. Here we present results from 3D thermo‐mechanical numerical simulations of convergence zones (including oceanic subduction followed by continental subduction/collision), in which we vary the rheological profile of the overriding plate (OP). For this, we systematically modify the crustal thickness of the overriding lithosphere and the temperature at the Moho to obtain a thermal thickness of the overriding lithosphere ranging from 80 to 180 km. While all models share a common global evolution (i.e., slab sinking, interaction between slab and the 660 km discontinuity, continental subduction/collision, and slab breakoff), they also highlight first‐order differences arising from the variations in the OP strength (thermal thickness). With a thin/weak OP, slab rollback is favored, the slab dip is low, the mantle flow above the slab is vigorous, and the trench migrates at a high rate compared to a thick/strong OP. In addition, slab breakoff and back‐arc basin formation events occur significantly earlier than in models involving a thick OP. Our models therefore highlight the major role played by the thickness/strength of the OP on convergence zone dynamics and illustrate its influence in a quantitative way. Key Points: We present 3D thermo‐mechanical lithospheric‐scale models of oceanic subduction followed by continental subduction/collisionWe show that the overriding plate thickness strongly impacts the convergence zone dynamics and the kinematics of the subduction eventsThicker overriding plate decreases mantle flow and trench mobility; it also controls overriding plate deformation and topography [ABSTRACT FROM AUTHOR]

Sedimentary archives of the westerlies‐influenced Pamir Plateau in Tajikistan, a climatically sensitive region in arid central Asia, provide information on past climatic changes and the tectonic evolution of the northern Tibetan Plateau. However, due to the scarcity of meteorological stations, knowledge of the recent precipitation history of the region is limited. We conducted a detailed rock magnetic investigation of 34 surface loess samples from the western Pamir Plateau. The results show that on the windward side, below an altitude of 2,000–2,200 m above sea level, the concentration of magnetic minerals initially decreases and then begins to increase with increasing altitude. Below 2,000–2,200 m above sea level, the surface soils are enriched in multidomain magnetite particles, suggesting a detrital origin of the magnetic minerals, whereas above this altitude the samples are enriched in fine superparamagnetic magnetite/maghemite grains of pedogenic origin. The inferred variations in pedogenic intensity, combined with analysis of the available meteorological data and the content of organic matter and clay, support the occurrence of an altitudinal threshold separating a predominantly detrital control on surface soil magnetic mineral assemblages from a predominantly pedogenic control. Within the plateau interior, the surface loess samples exhibit low and uniform values of magnetic concentration parameters and organic matter and clay content, which is attributed to the decreased supply of moisture from westerly sources because of the rain shadow effect. Our results indicate that rock magnetic investigations can be used to define a critical climatic boundary in arid central Asia. Key Points: At ~2,000–2,200 m a.s.l. pedogenesis replaces detrital input to dominant the magnetic properties of surface soils in the western Pamir PlateauRain shadow effect results in weak pedogenesis of the surface soils in the interior of the western Pamir PlateauRock magnetic properties can help identify a major climatic boundary in arid central Asia [ABSTRACT FROM AUTHOR]

Iron and stony‐iron meteorites form the Widmanstätten pattern during slow cooling. This pattern is composed of several microstructures whose length‐scale, composition and magnetic properties are dependent upon cooling rate. Here we focus on the cloudy zone: a region containing nanoscale tetrataenite islands with exceptional paleomagnetic recording properties. We present a systematic review of how cloudy zone properties vary with cooling rate and proximity to the adjacent tetrataenite rim. X‐ray photoemission electron microscopy is used to compare compositional and magnetization maps of the cloudy zone in the mesosiderites (slow cooling rates), the IAB iron meteorites and the pallasites (intermediate cooling rates), and the IVA iron meteorites (fast cooling rates). The proportions of magnetic phases within the cloudy zone are also characterized using Mössbauer spectroscopy. We present the first observations of the magnetic state of the cloudy zone in the mesosiderites, showing that, for such slow cooling rates, tetrataenite islands grow larger than the multidomain threshold, creating large‐scale regions of uniform magnetization across the cloudy zone that render it unsuitable for paleomagnetic analysis. For the most rapidly cooled IVA meteorites, the time available for Fe‐Ni ordering is insufficient to allow tetrataenite formation, again leading to behavior that is unsuitable for paleomagnetic analysis. The most reliable paleomagnetic remanence is recorded by meteorites with intermediate cooling rates (∼ 2–500 °C Myr −1) which produces islands that are "just right" in both size and degree of Fe‐Ni order. Key Points: Meteoritic cloudy zone formed at intermediate cooling rates can acquire a stable and reliable nanopaleomangetic remanence [ABSTRACT FROM AUTHOR]

Louis Neel's theories of thermoremanent magnetization (TRM) underlie all of rock magnetism. Neel's relaxation time equation for thermal activation of single-domain (SD) moments has been verified over geological time and temperature scales by laboratory thermal demagnetization of TRM overprints acquired in nature. For multidomain (MD) grains, disagreement with Neel's predictions is explained by re-equilibration of domain walls by the changing internal demagnetizing field during heating. Much effort has been devoted to testing the laws of additivity, reciprocity, and independence of partial TRMs, which partition the blocking temperature range and appear in nature as successive overprints of the original TRM. For SD grains, the laws are explained by Neel's theories and are verified experimentally. For MD grains, additivity holds but partial TRMs do not demagnetize over exactly the original blocking temperature interval (nonreciprocity) and are not entirely independent of one another when acquired in different directions. The current frontier in rock magnetism is to overcome this nonideal partial TRM behavior in order to extract precise and trustworthy records of ancient Earth's magnetic field directions and intensities. [ABSTRACT FROM AUTHOR]

Pliocene Vertisols from the Turkana Basin of northwest Kenya (~4°N latitude) have been examined using isothermal remanent magnetization (IRM) experiments, susceptibility measurements, and diffuse reflectance spectroscopy. The complete vertical profile of each paleosol is almost intact, measuring >2 m in thickness and being strongly magnetic (IRM at 1.0T ranges from 4 to 25 × 10−3 Am2/kg). Downprofile changes to the proxy indicators suggest uninterrupted pedodevelopment and a lack of stratigraphic inversions caused by argilli‐pedoturbation. Magnetic minerals consist of hematite to a lesser degree, and pedogenic ferrimagnets derived from moisture cycles that were controlled by monsoonal rainfall. Basal pedogenic zones of the paleosols are magnetically intense, and preserve the greatest slickenside development indicating pronounced seasonal wetting and drying. These observations indicate a deeper dry season water table as compared to poorly drained temperate/tropical Vertisols, which suffer reductive dissolution of Fe oxides in basal pedogenic horizons associated with weak magnetic intensities. Magnetic susceptibilities and the well‐represented presence of fine pedogenic ferrimagnets suggest that Pliocene rainfall was greater than the local modern rate of 200 mm/year and may have been within the range of 500–1,000 mm/year. The study highlights the need to expand the database on Vertisols Fe oxides and magnetism, especially considering the anomalously dry and bimodal rainfall seasonality of East Africa. Key Points: Monsoonal Vertisols of Pliocene Kenya have deep dry season water tables and are strongly magnetic relative to Vertisols at higher latitudesBimodal rainfall seasonality and the frequency of moisture extremes cause the redox conditions to produce high magnetite concentrationsMean annual rainfall during pedogenesis is estimated as <200 mm and between 500‐1000 mm, agreeable with other Pliocene records for the area [ABSTRACT FROM AUTHOR]

Sedimentary relative paleointensity (RPI) records are often carried by complex magnetic mineral mixtures, including detrital and biogenic magnetic minerals. Recent studies have demonstrated that magnetic inclusions within larger detrital silicate particles can make significant contributions to sedimentary paleomagnetic records. However, little is known about the role such inclusions play in sedimentary paleomagnetic signal recording. We analyzed paleomagnetic and mineral magnetic data for marine sediment core MD01‐2421 from the North Pacific Ocean, offshore of central Japan, to assess how magnetic inclusions and other detrital magnetic minerals record sedimentary paleomagnetic signals. Stratigraphic intervals in which abundant magnetic inclusions dominate the magnetic signal are compared with other intervals to assess quantitatively their contribution to sedimentary RPI signals. The normalized remanence record from core MD01‐2421 does not correlate clearly with global RPI stacks, which we attribute to a demonstrated lower paleomagnetic recording efficiency of magnetic inclusions compared to other detrital magnetic minerals. We also carried out the first laboratory redeposition experiments under controlled Earth‐like magnetic fields for particles with magnetic inclusions using material from core MD01‐2421. Our results confirm that such particles can be aligned by ambient magnetic fields but with a lower magnetic recording efficiency compared to other detrital magnetic minerals, which is consistent with normalized remanence data from core MD01‐2421. Our demonstration of the role of sedimentary magnetic inclusions should have wide applicability for understanding sedimentary paleomagnetic recording. Key Points: Sedimentary intervals rich in detrital magnetic mineral inclusions commonly record biased geomagnetic field intensity minimaRedeposition experiments of inclusion‐rich sediments indicate lower recording efficiency compared to inclusion‐poor samplesVariable recording efficiency of magnetic assemblages produces a bias that needs to be recognized in relative paleointensity records [ABSTRACT FROM AUTHOR]

Determination of ancient firing temperatures of archaeological pottery is a widely discussed topic in archaeometry. Here, a set of magnetic characteristics (magnetic susceptibility, isothermal and anhysteretic remanences, hysteresis parameters) and color parameters were studied for a collection of pottery fragments and burnt clay from house destructions. The results show that magnetite and hematite of superparamagnetic to single domain grain size are the main iron oxides produced during heating. Hematite fraction is more important and frequently detected in pottery sherds than in burnt clay from destructions. An inverse linear regression was obtained between the estimated firing temperature and the ratio value/chroma, which is shown to be site specific for pottery samples. For burnt house destructions, the regression is less well constrained and most probably reflects differences in the raw material. Consideration of rock-magnetic parameters against firing temperature estimates reveals a direct link between saturation magnetization and ancient firing temperature for burnt clay from house destructions. In contrast, this link is inverse and worse defined for pottery materials. This different behavior is attributed to different prevailing processes of iron oxide transformations in burnt clay and pottery, related to the specific firing conditions. [ABSTRACT FROM AUTHOR]

Magnetite and maghemite are important components of iron oxides that determine the magnetic properties of rocks, soils, and sediments, and are also materials with broad industrial applications. We investigated the reduction and transformation of both phases with a strain of sulfate-reducing bacteria (SRB). SRB growth resulted in 28.1% and 7.1% sulfate to acid volatile sulfur conversion in magnetite and maghemite, respectively. Transmission electron microscopy and X-ray photoelectron spectroscopy (XPS) analyses indicate that monosulfides (mackinawite and greigite) and polysulfides are the main secondary sulfides in the magnetite experiment, while the maghemite experiment also contained a high proportion of pyrite. XPS analyses indicate the reduction of Fe(III) to Fe(II) on the surface of magnetite and maghemite both by dissolved sulfides and SRB. Mössbauer spectroscopy measurements reveal the formation of superparamagnetic phases in microbial experiments, which indicates the dissolution and particle size decrease of the two minerals both by dissolved sulfides and SRB. X-ray diffraction and Mössbauer spectroscopy analyses suggest a complete transformation of nanomaghemite to nanomagnetite under the mediation of SRB through solid phase Fe(III) reduction. This transformation controls the changing and different patterns of both magnetic susceptibility and magnetic hysteresis for the two minerals. It is suggested that the structural similarity between magnetite and maghemite, and the conductivity of magnetite, constrain the unique solid phase transformation. Our findings indicate that the maghemite–magnetite solid solution is a potential natural battery for the growth of anaerobic microbes in sulfidic environments. [ABSTRACT FROM AUTHOR]

Apart from magnetostratigraphy, archaeomagnetism is rarely used in Middle and Late Pleistocene sites. Here we present detailed palaeomagnetic analyses of cemented hearths and burnt chert items from Amud Cave, Israel (68–55 ka) - two types of materials common in Levantine Middle Palaeolithic cave sites. Both materials are shown to be recorders of the geomagnetic field and were used to reconstruct either the ancient field direction (for cemented hearths) or intensity (palaeointensity) (for chert) at the time of the last burning or shortly after. We test the utility of palaeomagnetic data to further our understanding of temporal aspects of occupations in the cave by comparing the dispersion of the palaeomagnetic data to the known characteristics of geomagnetic secular variation in the Holocene. We show that divergent palaeointensities can help identify diachronic burning events, suggesting different activity patterns in two areas of the cave. Additionally, we used palaeomagnetic directional vectors to distinguish between a well-preserved hearth and one that had been mixed prior to cementation. Using rock magnetic investigations, we demonstrate that magnetic methods can be used as a relatively fast and inexpensive method to identify burning of cherts in antiquity above 500 °C. The palaeomagnetic results are in agreement with results of previous studies at Amud Cave, obtained by other independent methods. This study shows that palaeomagnetic methods can serve as a powerful tool in the study of Palaeolithic sites. [ABSTRACT FROM AUTHOR]

The Yermak Plateau is one of several regions in the Arctic Ocean where paleomagnetism yields controversial results. Despite low sedimentation rates, late Pleistocene paleomagnetic excursions have been reconstructed from many cores in the region, but they are characterized by considerably longer durations when compared to established ones. Self‐reversal during maghemitization of (titano)magnetite has been proposed as one explanation. Rock magnetic, 14C dating, sedimentological and stable isotope (δ18O) methods were employed to three new sediment cores to put paleomagnetic results in the context of the regional stratigraphy and chronology. Coherence of lithological parameters and δ18O variations validated the ratio of anhysteretic remanent susceptibility to bulk magnetic susceptibility (κARM/κ) as a parameter for cross‐core correlation. As established by earlier studies, we use the link between glacial/interglacial cycles and κARM/κ to tune our records to a global δ18O stack, which provides age models that are independent of radicarbon ages and paleomagnetic data. Our results show that zones of negative magnetic inclination are asynchronous across the plateau. Alternating field demagnetization data revealed that negative inclinations are contained in a medium‐high‐coercivity (>25–35 mT) magnetic phase that may be the result of postdepositional alteration of (titano)magnetite. We note a positive relationship between water depth and excursion duration, which may be driven by changes in water mass circulation on glacial/interglacial timescales. Key Points: New paleomagnetic and rock magnetic data from the Yermak Plateau (Arctic Ocean) are presentedWe link variations in magnetic grain size to changes in global oxygen isotope stratigraphy to construct independent age modelsBased on our age model approach, reconstructed paleomagnetic excursions are asynchronous [ABSTRACT FROM AUTHOR]

The Day diagram is used extensively in rock magnetism for domain state diagnosis. It has been shown recently to be fundamentally ambiguous for 10 sets of reasons. This ambiguity highlights the urgency for adopting suitable alternative approaches to identify the domain state of magnetic mineral components in rock magnetic studies. We evaluate 10 potential alternative approaches here and conclude that four have value for identifying data trends, but, like the Day diagram, they are affected by use of bulk parameters that compromise domain state diagnosis in complex samples. Three approaches based on remanence curve and hysteresis loop unmixing, when supervised by independent data to avoid nonuniqueness of solutions, provide valuable component‐specific information that can be linked by inference to domain state. Three further approaches based on first‐order reversal curve diagrams provide direct domain state diagnosis with varying effectiveness. Environmentally important high‐coercivity hematite and goethite are represented with variable effectiveness in the evaluated candidate approaches. These minerals occur predominantly in noninteracting single‐domain particle assemblages in paleomagnetic contexts, so domain state diagnosis is more critical for ferrimagnetic minerals. Treating the high‐coercivity component separately following normal rock magnetic procedures allows focus on the more vexing problem of diagnosing domain state in ferrimagnetic mineral assemblages. We suggest a move away from nondiagnostic methods based on bulk parameters and adoption of approaches that provide unambiguous component‐specific domain state identification, among which various first‐order reversal curve‐based approaches provide diagnostic information. Key Points: We assess 10 alternative approaches for domain state diagnosis as potential replacements for the much used but ambiguous Day diagramWe recommend adoption of methods that enable domain state identification of each component in samples with complex magnetic mineral mixturesWe conclude that magnetization curve analysis and FORCs provide the most diagnostic component‐specific domain state identifications [ABSTRACT FROM AUTHOR]

Magnetic signals in basalts from the Sylhet traps (ST), Shillong Plateau, India is investigated using rock magnetism as a proxy to explain the potentiality of the ST basalts as an indicator of magnetic mineralogy. A paleomagnetic study was carried out in order to unravel the Paleopole. In detail, rock magnetic and Anisotropy of Magnetic susceptibility (AMS) results have been reported for the first time on the ST basalts. A total of 38 oriented block samples were collected from 8 sites along Cherrapunji-Shella bazaar road section, Meghalaya, India. Samples were subjected to rock magnetic measurements such as magnetic susceptibility (K), Isothermal Remanent Magnetization (IRM), hysteresis loops, backfield (coercivity remanence) and k-T (Susceptibility vs. Temperature) analysis to identify the magnetic properties of basalts. Advanced Variable Field Translation Balance (AVFTB) was used for some rock magnetic studies. A few samples were also subjected to Anisotropy of Magnetic susceptibility (AMS) study to understand the petrofabric orientations and shape anisotropy in the ST basalts. The Remanence ratio (Mrs/Ms) and the Coercivity ratio (Bcr/Bc) ranging from 0.105 to 0.333 and from 1.25 to 1.87 respectively indicate sizes of magnetic grains are mainly in the range of Pseudo Single Domain (PSD) limits with minority of them in the ranges of Single Domain (SD) limits. The results of k-T study in combination with other rock magnetic results shows that magnetite (Fe 3 O 4) [Curie Temperature = 565-590 °C] as the dominant magnetic carrier with a subordinate content of titanomagnetite Fe2+(Fe3+Ti) 2 O 4 [Curie Temperature = 380–450 °C]. From the AMS study, parameters like lineation, foliation are calculated, and results define all the three shape anisotropies present in the ST basalts. The ST basalts display paleomagnetic directions with mean declination = 255°, mean inclination = -57° (α 95 = 3.44°; k = 16.74). The pole position of the ST at 117 Ma is -26.79 °N, 330.75 °E (dp = 3.6; dm = 5) with a paleolatitude 37.6 °S. This infers that the ST is a later volcanic event than Rajmahal traps (RT) which is considered contemporary to the ST. [ABSTRACT FROM AUTHOR]

We implement a spectral-infinite-element method (SIEM) to compute magnetic anomalies by solving a discretized form of the Poisson/Laplace equation. The SIEM combines the highly accurate spectral-element method with the mapped-infinite element method, which reproduces an unbounded domain accurately and efficiently. This combination is made possible by coupling Gauss–Legendre–Lobatto quadrature in spectral elements with Gauss–Radau quadrature in infinite elements along the infinite directions. Our method has two distinct advantages over traditional methods. First, the higher-order discretization accurately renders complex magnetized heterogeneities. Second, since the computation time is independent of the number of observation points, the method is efficient for very large models. We illustrate the accuracy and efficiency of our method by comparing calculated magnetic anomalies for various magnetized heterogeneities with corresponding analytical and commonly used computational solutions. We conclude with a practical example involving a complex 3-D model of an ore mine. [ABSTRACT FROM AUTHOR]

The scarcity of reliable paleomagnetic secular variation (PSV) records from East Asia especially from low‐latitude regions impedes better understanding of global PSV mechanisms. Here we report on a radiocarbon‐dated Holocene PSV record from a composite ~6.7‐m‐long core collected from the high‐sedimentation‐rate Huguangyan Maar Lake (HML) in subtropical‐tropical South China. Rock magnetic results demonstrate that the natural remanent magnetization resides in single‐domain magnetite. Alternating field demagnetization experiments at 1‐cm spacing on u‐channel samples reveal six distinct inclination highs at ~7,500 BCE, ~5,100 BCE, ~4,600 BCE, ~3,600–3,400 BCE, ~1,600–1,200 BCE, and 600–800 CE; three inclination lows at ~4,800 BCE, ~600–300 BCE, and ~1,000–1,300 CE; and three eastward declination trends at ~3,600–3,200 BCE, ~2,600–2,400 BCE, and 400 BCE to 200 CE. The similarity between the HML PSV record and other independently dated records from East Asia and geomagnetic field models corroborates the robustness of our age model and Holocene PSV record. Strikingly, centennial‐ to millennial‐scale PSV features of the HML are comparable, within age uncertainties, with other Holocene records from Europe, North America, and Canada, suggesting that such directional patterns are likely to be hemispheric in scale. Although relative paleointensity data of HML are affected by environmental factors (e.g., organic matter diagenesis), the record still provides a regionally important new PSV reference curve whose conspicuous features may serve as stratigraphic markers for East Asian paleorecords. Key Points: A well‐dated high‐resolution paleomagnetic secular variation record throughout the Holocene from Huguangyan Maar Lake is presentedThis PSV record broadly agrees with typical sediment records from East Asia, Europe, North America, and geomagnetic field model predictionsThis record may be used as a reliable PSV reference curve and a valuable tool for regional correlation and dating purpose in South China [ABSTRACT FROM AUTHOR]

Abstract Magnetic properties of lunar rocks may help understand the evolution of the past magnetic field of the Moon. However, these properties are often measured on small subsamples, which may not be representative of the bulk lunar rocks. In this study, a rough magnetic characterization of a large fraction of the Apollo collection was performed using non-destructive methods, with a focus on large samples (mean mass 500 g). The natural remanent magnetization of 123 Apollo samples and the magnetic susceptibility of 154 Apollo samples were measured in the Apollo storage vault at the Lunar Sample Laboratory Facility in Houston. Magnetic susceptibility is strongly controlled by lithology and is clearly enhanced by impact processing and associated incorporation of meteoritic metal, as well as formation of nanometric iron particles by space weathering. The natural remanent magnetization is lower by a factor of ~3 than that measured on small samples (~100 mg), suggesting magnetic contamination during small-sample preparation or handling, or directional heterogeneity in remanence within large samples. The ratio of natural remanence magnetization to magnetic susceptibility may be used as selection tool for further paleomagnetic study. It is a crude paleointensity proxy and its overall temporal evolution is coherent with the existence of a high magnetic field from ~4 Ga to 3.5 Ga and a subsequent weaker field epoch as previously defined in the literature. Our data also raise the possibility that the intensity of the paleomagnetic field during the high field epoch may have been more variable and lower on average than previously suggested. Highlights • 161 large Apollo lunar samples were studied for magnetic properties in the LSLF (Houston). • Magnetic properties are primarily controlled by impact processing. • The ratio of remanence to susceptibility can be used for sample selection for laboratory study. • This ratio is a crude proxy to paleointensity. [ABSTRACT FROM AUTHOR]

Drill rock cuttings from different depths of two geothermal wells (Az-26 and Az-49) from the Los Azufres Geothermal Field (LAGF), Mexico, were analyzed for rock magnetic properties (magnetic susceptibility, χ lf ; frequency-dependent susceptibility, χ fd; susceptibility of anhysteretic remanent magnetization, χ ARM ; isothermal remanent magnetization, IRM; saturation isothermal remanent magnetization, SIRM; "hard" isothermal remanent magnetization, HIRM) and their inter-parametric ratios (SIRM/ χ lf , χ ARM /SIRM and S-ratio) to explore the relationship, if any, between these properties and hydrothermal alteration. In both the geothermal wells, the intensity of hydrothermal alteration increases with depth and temperature of the well. The samples exhibit hydrothermal alteration-induced changes in several rock magnetic properties: (1) a decreasing trend in the values of concentration-dependent rock magnetic parameters (χ lf ; χ fd, χ ARM , IRM 300mT , and SIRM); (2) a decrease in S-ratio (relative proportions of ferrimagnetic and anti-ferromagnetic minerals) values and an increase in HIRM ("hard" IRM; concentration of magnetically "hard" minerals, e.g., hematite) values; and (3) increasing SIRM/ χ lf and χ ARM /SIRM ratio values. Most of the rock cuttings in both the wells are characterized by coarse SSD grains and they exhibit χ lf values between 1 × 10−6 m3kg−1 (acid igneous rocks) and 10 × 10−6 m3kg−1 (SSD/MD grain size). Our study also indicates that the initial (primary) mineralogy of reservoir rocks may have an influence on the type of hydrothermal minerals that would form at low reservoir temperatures and/or with low intensity of hydrothermal alteration; however, this may not have any significant influence at high reservoir temperatures and/or high intensity of hydrothermal alteration. Our study suggests that in a homogenous litho-unit (rocks of the same type and age) of a large area, a zone characterized by anomalously low values of concentration-dependent rock magnetic properties (χ lf , χ fd, χ ARM , IRM 300mT and SIRM), high SIRM/ χ lf , χ ARM /SIRM and HIRM values and low S-ratio values may indicate intense hydrothermal alteration. Consequently, rock magnetic properties may be a simple, yet an important tool, to identify hydrothermally altered rocks and zones of hydrothermal alteration, particularly in the initial stages of geothermal exploration. • Application of rock-magnetic properties in identification of hydrothermally altered rocks. • Characteristics of magnetic grain-size and magnetic domains in relation to hydrothermal alteration. • Rock magnetic properties may be useful tools in the initial stages of geothermal exploration. [ABSTRACT FROM AUTHOR]

Based on detailed studies of the anisotropy of magnetic susceptibility (AMS), the directions of magmatic-melt propagation have been reconstructed in large dolerite sills of the Angara--Taseeva syneclise. Half the sites studied showed a magnetic fabric of "normal" type, i.e., the minimum K3 axis of the AMS ellipsoid is orthogonal to the contact, and the other two axes lie in the plane of the intrusive body. Interpreting the orientation of the maximum K1 axis as the direction of the melt flow at such sites, we compiled a scheme of the main magma flow directions. The obtained results are generally consistent with the hypothesis of magma-feeding zone in the central, most downwarped part of the Angara--Taseeva depression. The distribution of the maximum axes of the AMS ellipsoid is different in sills and points to the existence of local intrusion centers. Intrusions with an AMS ellipsoid of "reverse" type are predominant on the periphery of the depression. The sites with a "normal" magnetic fabric do not demonstrate any prevailing direction of magma propagation, because there is no general direction of the melt flow in the peripheral subsurface zones of large intrusions. [ABSTRACT FROM AUTHOR]

Understanding of the processes of magmatic fabric formation in crystal‐rich magmas and their reflection in rock magnetic properties are important for understanding pluton formation and intrusion mechanisms. On the example of small concentrically zoned Castle Crags pluton in the Klamath Mountains (CA, USA) we provide reconstruction of the flow/deformation mechanisms of the crystal‐rich magma and pluton growth based on detailed structural mapping and microstructural analysis employing the anisotropy of magnetic susceptibility, microstructural analysis, and crystallographic preferred orientation. Our study reveal microstructural evidence for progressive development of magmatic textures in the pluton core transitioning to submagmatic and eventually subsolidus fabric at the pluton periphery, that is interpreted in terms of the flow/deformation of the crystal mush. The documented magmatic textures are linked to anisotropy of magnetic susceptibility parameters and orientation. The recorded anomalous degree of anisotropy of magnetic susceptibility found in the pluton is attributed to tiling and plastic deformation of magnetite grains by the surrounding phenocrysts. The concentric structure of the pluton resulted from horizontal compaction and margin parallel stretching of the dense crystal mush around the vertically intruding trondhjemite magma in the pluton core. The Castle Crags pluton is interpreted as a concentrically expanded pluton, which grew at least by two increments of granodiorite and trondhjemite magma emplacement. Key Points: Joint structural, magnetic, and microstructural analysis reveals growth‐related flow and deformation of granitic crystal mushThe pluton reveals concentric structure of magmatic, submagmatic, and locally subsolidus texturesAnomalous intensity magnetic fabric results from indentation and tiling of magnetite during submagmatic and cumulate texture formation [ABSTRACT FROM AUTHOR]

Magnetic properties from the Reinfjord Ultramafic Complex, in northern Norway, which formed as part of a deep magmatic conduit system, have been investigated to determine the magnetic signature of ultramafic rocks now exposed at the surface and deeper in the lower crust. The dominant carriers in these ultramafic rocks are a chrome‐spinel with Fe‐rich exsolution blebs and exsolution lamellae of magnetite in clinopyroxene. Except locally, in a fault zone and in discrete small fractures, these rocks show only minor to no alteration. We infer that the magnetic oxides characterized here are representative of pristine magnetic carriers in similar rocks deeper in the crust. These oxides can be stable in lower crustal, possibly upper mantle, depths when temperatures are below the Curie temperature of magnetite, taking into account pressure effects. These ultramafic rocks are candidates for potential sources of long‐wavelength anomalies. Plain Language Summary: Satellites are used to map the Earth's magnetic field and explore magnetic anomalies created by this field in crustal rocks. To understand the magnetic signal from deep‐seated rocks, we need to explore the sources and nature of the magnetic mineralogy. This paper reviews the magnetic properties of rocks that formed deep in the Earth's crust (at 25‐ to 35‐km depth), 570–560 million years ago, now well exposed in Northern Norway. Despite a history of being exhumed from deep in the crust, these rocks only show minimal alteration and present a rare opportunity to study their pristine magnetic properties. The primary magnetic minerals in these ultramafic rocks are an exsolved chrome‐spinel, and magnetite lamellae in clinopyroxene. These minerals formed at high temperatures and could be representative of minerals residing deeper in the lower or upper mantle. These phases are magnetically stable up to the Curie temperature of magnetite. These ultramafic rocks are a potential source of magnetization in the lower crust and the upper mantle. Key Points: Primary magnetic oxides are chrome‐spinel with Fe‐rich exsolution lamellae and magnetite lamellae in pyroxeneThese carriers are stable at lower crust to uppermost mantle conditionsUltramafic rocks are potential sources of long‐wavelength‐anomalies [ABSTRACT FROM AUTHOR]

Abstract Paleomagnetic and rock magnetic studies performed on sediment cores from Laguna Cháltel (Patagonia, Argentina) show strong and stable remanence carried by pseudo-single domain (PSD) magnetite. Concentration of magnetic minerals varied between 0.01 and 0.08%. Paleomagnetic records from four cores document little scatter of directions with very good inter-site correlation. The new paleosecular variation curve from Laguna Cháltel extends to 4700 cal. BP and was compared with other records from Patagonia, including lacustrine records from Lakes El Trébol, Moreno, Escondido, Carmen and Laguna Potrok Aike. These results represent a major step forward in constructing a Paleosecular Variation (PSV) type curve for southern Argentina that can be used to improve stratigraphic correlation of sedimentary sequences. Highlights • A new Holocene record of geomagnetic secular variation from Southern Argentina is presented. • Two noticeable minima in inclination and declination at about 3450 and 3800 cal years BP are confirmed. • The results encourage us to deduce a general pattern for Southern of South America. [ABSTRACT FROM AUTHOR]

Abstract A combined study of rock-magnetism and electronic-paramagnetic resonance (EPR) was performed in core samples from an oil well in the Vaca Muerta Formation (SW Argentina). The aim of this work was to characterize the effects of hydrocarbon-related diagenesis on the magnetic signature of oil shales. Similar research has been previously conducted in near-surface sediments affected by oil and gas microseepage, so as to establish a relationship between micromagnetic anomalies and the underlying reservoirs. The EPR technique was employed to measure minute concentrations of organic matter free radicals (OMFRs), Fe3+ and Mn2+. These results, and the concentrations of extractable organic matter (EOM), were compared with mass-specific magnetic susceptibility (χ) and natural remanent magnetization (NRM). The reactive OMFRs, resulting from the thermal degradation of a kerogen that yields a slightly-biodegraded crude oil, seem to have acted on the primary Fe oxides and sulfides through two diagenetic stages. The first stage might have partially dissolved these minerals. Consequently, a number of depth levels show a decrease of both χ and NRM, against an increase of the OMFRs. On the other hand, for a core-interval between 2663 and 2695 m (P18/P24), a second diagenetic stage could have produced partial replacement of framboidal pyrite by authigenic pyrrhotite, as recognized by scanning electron microscopy (SEM), electron X-ray energy dispersion (EDX) experiments and the analysis of the thermomagnetic and IRM curves. Thus, within P18/P24, magnetic parameters increase in direct proportion with the amount of OMFRs. The lithologies encompassed by P18/P24 show small levels of Mn2+, a proxy directly related to calcareous cementation. Moreover, Gamma Ray, resistivity and neutron porosity well logs reveal distinctive features for P18/P24, as well as an increase of hydrocarbon content, contrasting with the rest of the section analyzed. The hydrocarbon-induced magnetic anomalies in these oil shales seem to be conditioned mostly by their petrophysical properties. Highlights • First study linking hydrocarbons and magnetic signatures in oil shales/source rocks. • Organic matter free radicals (OMFR) appear to reduce primary magnetic Fe oxides and sulfides in oil impregnated rocks. • Magnetic anomalies (e.g. χ) seem to be conditioned by the petrophysical properties of reservoir/source rocks. • Positive ratios of magnetic/EPR data (e.g. Δχ/ΔOMFR) might indicate anomalous oil targets in reservoir/source rocks. [ABSTRACT FROM AUTHOR]

Highlights • Low absolute paleointensity is discovered during Late Miocene Noma excursion at 6.66 ± 0.45 Ma. • Paleointensity variation reveals a 'V-shape' of high–low–high paleointensities during the excursion. • The paleointensity decreases down to 1.9 ± 0.3 µT as the excursion progresses. • The VDM is 0.3–1.1 × 1022 Am2 during the Noma excursion. Abstract Paleointensity variation is investigated for a sequence of andesitic lavas which records the Noma geomagnetic excursion at 6.66 ± 0.45 Ma. Sixty-six samples are collected from 11 lava flows at the Kamegaoka Mountain (31° 21′N, 130° 13′E) on the Noma Peninsula, Kyushu Island, Japan. Rock magnetic experiments confirm the presence of Ti-poor titanomagnetite grains with pseudo-single-domain or a mixture of single and multi-domains as the carrier of the remanent magnetization. The application of the Tsunakawa-Shaw method yields reliable geomagnetic paleointensity data set of 29 samples from 9 lavas that cover the Noma excursion. The mean paleointensities of lava flows vary from 1.9 to 10.3 µT. Paleointensity variation reveals a 'V -shape' of high–low–high paleointensities during the excursion. The highest value of 10.3 ± 3.5 µT appears prior to the excursion, the paleointensity decreases down to 1.9 ± 0.3 µT as the excursion progresses, and the paleointensity finally regenerates to 5.1 ± 3.0 µT at the end of the excursion. The virtual dipole moment (VDM) during the Noma excursion (0.3–1.1 × 1022 Am2) is less than 16% of the mean VDM during the period between 4 and 8 Ma in Miocene, suggesting that this weak geomagnetic field intensity is ascribed to the nature of excursions rather than the Miocene geomagnetic field properties. The weakest VDM (0.3 × 1022 Am2) in the Noma excursion is detected at the pole position that is located at fairly high latitude (58.9°N) in the opposite hemisphere. The Noma excursion is characterized by a large shift in virtual geomagnetic poles of more than 140° from the geographic pole and by a weak VDM of 1.0 × 1022 Am2 or less. [ABSTRACT FROM AUTHOR]

We report here on results of palaeo- and rock magnetic investigations of two sediment cores from the Upper Congo deep-sea fan. The sediments have a high organic content and contain a heterogeneous Fe-mineral assemblage with biogenic magnetite and detrital (Ti-)magnetite as the main magnetic carrier minerals. Pyrite, hematite, and Fe-oxyhydroxides were identified by comparing high-temperature magnetic susceptibility curves with those from Fe-minerals of known composition. According to AMS 14C dates, the 6.8 m-long profile spans the last 37 kyr. Sediments older than 20 ka are affected by reductive diagenesis that has led to a loss of the fine-grained magnetic mineral fraction. Sediments younger than 20 ka have stable magnetizations. Characteristic remanent magnetization records of inclination and declination were obtained for each core. There is a little agreement between these records, modelled curves, and other sediment records from Equatorial Africa, so no composite record could be established. The cores are not ideal relative palaeointensity recorders and estimates using different normalizers did not yield consistent signals from both cores. Normalization methods used for relative palaeointensity estimation were not developed for sediments that contain large amounts of ultra-fine-grained biogenic magnetite; therefore, the relative palaeointensity estimates should be considered with caution. However, in view of the incoherent picture given by the scarce available palaeointensity information from the region off South-West Africa, the GeoB6517-2 record may provide a tentative relative palaeointensity record for comparison, at least for the past 10 kyr. [ABSTRACT FROM AUTHOR]