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The Neoproterozoic carbonate rocks of the Araras Group (Amazon Craton) and the Sete‐Lagoas and Salitre Formations (São Francisco Craton) share a statistically indistinguishable single‐polarity (reversed) characteristic direction. This direction is associated with paleomagnetic poles that do not align with the expected directions for primary detrital remanence. We employ a combination of classical rock magnetic properties and micro imaging/chemical analysis (in thin sections) using synchrotron radiation to examine these remagnetized carbonate rocks. Magnetic data indicate that most samples lack the anomalous hysteresis properties typically associated with carbonate remagnetization (except for distorted loops). Through a combination of Scanning Electron Microscopy with Energy Dispersive X‐ray Spectroscopy (SEM‐EDS), X‐ray Fluorescence (XRF), and X‐ray Absorption Spectroscopy (XAS), we identified subhedral/anhedral magnetite, or spherical grains with a core‐shell structure of magnetite surrounded by maghemite. These grains are within the pseudo‐single domain size range, as do most of the iron sulfides, and are spatially associated with potassium‐bearing aluminosilicates. While fluid percolation and organic matter maturation play a role, smectite‐illitization appears to be crucial for the growth of these phases. X‐ray diffraction analysis, in addition, identifies these silicates as predominantly highly crystalline illite, suggesting exposure to epizone temperatures. These temperatures were likely reached during the final stages of the Gondwana assembly (Cambrian), but remanence was only locked in afterward, in successive cooling events during the Early Middle Ordovician. This is supported by the carbonates' paleomagnetic pole positions compared to Gondwana's apparent polar wander path, and the absence of reversals, contrasting with the high reversal frequency of the Late Ediacaran/Cambrian. Plain Language Summary: Carbonate rocks serve as important records of ancient climates and host magnetic minerals capable of documenting the evolution of Earth's magnetic field. Nevertheless, their original magnetization, acquired during sedimentation, is frequently supplanted by a secondary magnetization, originating from various geological processes altering local thermochemical stability. For carbonate rocks, this remagnetization process is often associated with a "magnetic fingerprint." In South America, carbonate rocks from different sedimentary basins (hundreds of kilometers apart) exhibit statistically similar magnetic components that deviate from their formation origin, indicating secondary processes. This multidisciplinary study integrates classical paleomagnetic analysis with micro‐chemical and imaging analysis to comprehend the geological phenomena responsible for remagnetizing such an extensive continental area. We demonstrate that not all remagnetized samples display the anticipated magnetic fingerprint. Highly detailed chemical analysis confirms the presence of nanoscopic magnetic minerals spatially correlated with clay minerals indicating that while organic matter transformation may play a significant role, clay mineral transformation is a key phenomenon governing remagnetization in these rocks. However, our data also supports the notion that these rocks underwent heating during the final assembly of the ancient continental landmass, Gondwana, and a sequential cooling event is suggested as locking their magnetization in the state observed today. Key Points: Remagnetized Neoproteorozoic carbonates in Brazil may not consistently display anomalous hysteresis parametersSynchrotron‐based analysis revealed pseudo‐single domain‐sized magnetite spatially correlated with aluminosilicates (smectite‐illite)The Late Cambrian assembly of Gondwana thermally reset the carbonates' remanence, eventually blocking it (470–460 Ma) during gradual cooling [ABSTRACT FROM AUTHOR]

Herein, we report an improvement over Hartmann-Hahn cross polarization for NMR signal enhancement: adiabatic demagnetization/remagnetization transfers that provide up to a 9-fold experimental speedup for 13 C NMR signals in amino acids over conventional means. The experiment proved insensitive to site type, and we also demonstrate a means for making it compatible with high-resolution spectroscopy.

The drift history of the Lhasa terrane plays an essential role in understanding the tectonic evolution of the Bangong-Nujiang Tethyan Ocean and the Neo-Tethyan Ocean, as well as the evolutionary history of the Tibetan Plateau. Here, a combined rock magnetic, petrographic, and palaeomagnetic study is performed on the Upper Permian–Lower Triassic limestones (∼259–251 Ma) in the western Lhasa terrane. The site-mean direction for the 28 sites is D g = 32.1°, I g = 50.3°, k g = 47.9 and α 95 = 4.0° in situ and D s = 342.9°, I s = 32.7°, k s = 43.2 and α 95 = 4.2° after tilt-correction, yielding a palaeopole at 68.9°N, 314.4°E with A 95 = 4.3°, corresponding to a palaeolatitude of 18.0° ± 4.3°N. The fold tests are not significant because the sampling section shows monoclinic features with minor variations in their bedding attitudes. The palaeopoles for the directions before and after tilt-correction are compared with reliable Late Permian–Palaeogene palaeopoles obtained from the Lhasa terrane. Based on these comparisons, the studied limestones were remagnetized prior to tilting and this remagnetization most likely occurred during the Early Cretaceous. The depositional environment of the limestones may have changed from anoxic to suboxic and oxic during the Early Cretaceous, leading to the oxidation of iron sulphide to authigenic magnetite. Meanwhile, the Late Jurassic–Early Cretaceous convergence between the western Lhasa and Qiangtang terranes may have resulted in tectonic fluid migration and the formation of calcite veins and stylolites in the limestones. This is supported by the presence of small calcite veins and stylolites in some samples, as well as the fact that the framboidal oxides were formerly sulphides (mostly pyrite), implying that the majority of the iron oxides observed in the limestones were authigenic. These processes indicate that chemical remanent magnetization caused by the growth of magnetic minerals related to tectonic fluid migration was most likely the mechanism for the limestone remagnetization. [ABSTRACT FROM AUTHOR]

Variable flux memory machines (VFMMs) have become a research hotspot due to their adjustable air-gap flux with the employment of low coercive force (LCF) permanent magnets (PMs). Series hybrid magnet VFMMs (SHM-VFMMs) utilizing series-magnetic-circuit high coercive force (HCF) and LCF PMs are extensively investigated due to their excellent unintentional demagnetization (UD) withstand capability. Nevertheless, the existing researches still focus on the UD of LCF PMs under heavy load operation, and the remagnetization issue remains unreported. Therefore, in this paper, the over-load unintentional remagnetization (UR) effect of the a dual-layer-SHM-VFMM (DLSHM-VFMM) is first revealed, and its mechanism is investigated and analyzed in depth based on finite element (FE) analyses. A DLSHM-VFMM prototype is manufactured and tested to verify the effectiveness of the theoretical analyses.

Increases in temperature and pressure caused by rapid burial of sediments seaward of the Sumatra subduction zone have been hypothesized to trigger dehydration reactions that diagenetically strengthen sediments and contribute to the formation of an over‐pressured pre‐décollement, which together facilitate the occurrence of large shallow earthquakes. We present paleomagnetic, rock magnetic, and electron microscopic analyses from drill cores collected offshore Sumatra at Site U1480 during IODP Expedition 362 that support this hypothesis. The older pre‐fan units (Late Cretaceous to early Paleocene) were deposited when Site U1480 was moving rapidly northward with the Indian plate from a paleolatitude of 50° to 30°S, which would equate to expected absolute paleomagnetic inclinations of 70°–43°. Most of the older pre‐fan sediments, however, have shallow observed inclinations (shallower than ±20°), indicating that the sediments were overprinted when Site U1480 was located near the paleoequator, as it has been since the early Oligocene. Electron microscopic observations reveal that the pre‐existing detrital magnetite grains have undergone pervasive dissolution and alteration by hydrothermal fluids. The diagenesis observed is consistent with mineral dehydration, possibly driven by rapid burial of pelagic sediments by the ∼1250 m thick Nicobar Fan sequence. In addition, the elevated burial temperature also facilitated the smectite to illite conversion reaction. We hypothesize that chemical reactions resulted in the formation of fine‐grained magnetite that records a chemical remanent magnetization overprint. This overprint is consistent with the alteration occurring after burial by the thick Nicobar Fan sequence sometime in the past few million years. Plain Language Summary: Sediments and rocks commonly contain magnetic minerals that record the direction and intensity of Earth's magnetic field as they are being emplaced, thus preserving an ancient record of the geomagnetic field. Subsequent alteration of the magnetic minerals caused by heating and/or fluid circulation can result in the acquisition of secondary magnetizations (i.e., remagnetization) that may overprint or completely reset the primary ancient magnetization. Such remagnetization provides evidence of the physical and chemical changes that have occurred. Here through paleomagnetic, rock magnetic, and microscopic analyses of the deeper older (pre‐fan) stratigraphic sequence cored offshore Sumatra, we find that hydrothermal fluids, resulting from mineral dehydration driven by rapid burial of this sequence by younger, thick Nicobar Fan sediments, led to pervasive secondary remagnetization. Consequently, the newly formed magnetite recorded a much younger paleomagnetic field, leaving a shallow overprint that probably occurred sometime in the past few million years. The dehydration reactions also increased the strength of the sediments entering the subduction zone and aided in the formation of slip surfaces (called décollements), possibly contributing to the shallow, large earthquakes that have generated tsunamis off Sumatra. Key Points: The 60–67 Ma pre‐fan sediments offshore Sumatra were most likely remagnetized since deposition of the Nicobar Fan sediments, which began at ∼9 MaRemagnetization of pre‐fan sediments caused by mineral dehydration may be linked to shallow seismogenic slip off SumatraMagnetic properties of input sediments in the subduction margin record conditions that may have facilitated the generation of earthquakes [ABSTRACT FROM AUTHOR]

Carbonate rocks, widely used for quantifying paleolatitude of the Gondwana‐derived terranes on the Tibetan Plateau and the geodynamic evolution of the Tethyan Oceans, are prone to remagnetization. However, diagnosing such secondary remanent magnetization is difficult and the mistakes have induced confusion in paleogeographic reconstructions. To evaluate if the Upper Triassic limestones of the Duoburi Formation from the Lhasa terrane carry a primary remanence, we report comprehensive rock magnetic, diffuse reflectance spectroscopic, and petrographic results of these rocks. We discover that magnetic carriers vary systematically from magnetite to magnetite plus minor hematite/goethite to hematite/goethite plus minor magnetite with change of rock color and demagnetization behavior of the specimens. Most magnetite and all hematite/goethite grains have clear authigenic origin and were possibly formed during oxidation of early diagenetic pyrite. Such a process was likely assisted by oxic fluid circulation as shown by omnipresent calcite veins within the rocks. These authigenic iron oxides have widely distributed grain sizes with most of them being superparamagnetic at room temperature. Detrital (titano)magnetite is also recognized in some specimens, but its concentration is much lower than that of the authigenic magnetic grains. Based on these results, we conclude that limestone from the Duoburi Formation was remagnetized due to fluid circulation during late diagenesis. We discuss criteria used for diagnosing remagnetization in carbonate rocks, and suggest that a robust evaluation of the remanence origin should integrate field tests, statistics of the remanence direction, rock magnetic properties, and petrographic observations with the limits of each criterion being carefully considered. Plain Language Summary: The Lhasa terrane from the central Tibetan Plateau was one of the continental blocks that rifted from the Gondwana supercontinent, drifted northward, and accreted to Eurasia in the Mesozoic. Paleolatitude determined by paleomagnetism can provide quantitative information which is critical to restore these geodynamic processes. However, paleomagnetic investigations on the ancient carbonate rocks on the Tibetan Plateau are often troubled by remagnetization, a process during which the primary remanent magnetization acquired during or soon after formation of the rocks was replaced by secondary remanent magnetization with an unknown younger age. In this study, we provide an example of Upper Triassic limestones from the Lhasa terrane. Within these rocks, detrital (titano)magnetite, which can carry a primary magnetic signal, was mostly altered, and nonmagnetic pyrite largely transformed to authigenic magnetite/hematite/goethite, which acquired remanent magnetization at an unknown later time. The magnetic record from these rocks thus cannot be used to determine the Late Triassic paleolatitude of the Lhasa terrane. Our analysis reveals the most common mechanisms of remagnetization in carbonate rocks. More importantly, we provide universal tools and criteria that can be used in future paleomagnetic studies of carbonate rocks to evaluate their remanence origin. Key Points: Magnetic carriers of the Duoburi Formation limestone are authigenic magnetite, hematite and goethite and little detrital titanomagnetiteLimestones of the Duoburi Formation were remagnetized due to circulation of oxic fluid through the rock at a late stageDiagnosis of remagnetization in carbonate rocks should integrate different criteria but consider the limits of each criterion carefully [ABSTRACT FROM AUTHOR]

Robust paleomagnetic results through geological time are one of the keys to understand the drift history of the eastern Qiangtang terrane (EQT). Here, we presented comprehensive petrographic observations and rock magnetic and paleomagnetic analyses of the early Carboniferous Upper Zaduo (ZD) limestone Formation (C1z2) from the Sulucun (SLC) section in the Zaduo area, EQT, to investigate its magnetic originality and geological significance. A total of 12 sites (131 samples) were collected. Photomicrograph observations indicate that the limestone samples were characterized by widespread carbonate veinlets. Electron microprobe and energy dispersive spectrometry analyses confirm that authigenic magnetite formed after pyrite. Rock magnetic analyses reveal the dominant magnetic minerals of pyrite and magnetite, with ‘wasp-waisted’ hysteresis loops and close to the “remagnetization trend” hysteresis parameters. Based on both thermal and alternating field demagnetizations, the characteristic remanent magnetization directions for most samples were isolated: Dg = 6.3°, Ig = 50.1°, kg = 54.9, α95 = 6.2° in-situ, and Ds = 330.2°, Is = 58.9°, ks = 5.9, and α95 = 20.5° after 2-step tilt correction. The κ (α95) value decreases (increases) after tilt-correction, and the ChRM directions failed both the McFadden (1990), Watson and Enkin (1993) fold tests, indicating post-folding magnetizations. The 11 site-mean directions yield a mean in-situ paleopole of 84.4°N, 200.3°E, and A95 = 6.8°, which is coincident with the post ∼53 Myr (especially around 40 Ma) paleopoles of the region. We therefore interpreted that these early Carboniferous limestone samples contain remagnetized magnetizations and that they were obtained after 53 Ma, most likely around 40 Ma, due to the far-field effect of the India–Eurasia collision.

Abstract—In the paper, we present the results of paleomagnetic studies on numerous intrusive bodies of the Bashkirian megazone, a major tectonic zone of the Southern Urals. More than 70 intrusions in various parts of the Bashkirian megazone (in the northern, central, and southern part of the structure) were sampled. The studied intrusions have Riphean age. However, as a significant part of the rocks of the Southern Urals, these intrusive bodies were remagnetized during the Late Paleozoic collision within the Urals fold belt. Here, we discuss the secondary Late Paleozoic component of natural remanent magnetization. According to the obtained paleomagnetic data, the secondary Late Paleozoic component in most of the Bashkirian megazone is post-folding, i.e., formed after the completion of the main phase of fold deformations in the Southern Urals. A comparison of paleomagnetic directions obtained from intrusions in different parts of the Bashkirian megazone showed that there were no significant movements of individual parts of the Bashkirian megazone relative to each other after the formation of the Late Paleozoic component. The Late Paleozoic remanence component yielded a paleomagnetic pole of Plong = 171.6°, Plat = 39.9°, α95 = 5.9°, and N = 6 from six regions (38 sites) in the Bashkirian megazone. The obtained pole is statistically indistinguishable from the mean of 15 poles for Stable Europe with ages of 280–301 Ma. Thus, the secondary Late Paleozoic component in the Bashkirian megazone formed approximately 280–301 million years ago, after which the Bashkirian megazone did not experience any relative motions with respect to the East European craton. [ABSTRACT FROM AUTHOR]

Four different switching scenarios have been revealed for a linear chain of flat magnetic particles with long axes perpendicular to the axis of the chain. The diamond-like shape of the particles has been previously shown to be the best to ensure a uniform and stable magnetization within a single particle, that is, to behave as a macrospin. The occurrence of each scenario depends on the distance of the particles in the chain. Whereas long distances favor direct remagnetization of a ferromagnetic configuration “all up” to the one “all down”, a short enough distance allows the system to recover its ground state at a zero field, that is, an antiferromagnetic order. This allows any information stored by a magnetic field to be erased. Vortex-like metastable defects have been noticed for intermediate distances. A longitudinal magnetization component at extremely short distances has been noticed as well as specific systems of domain walls. The hysteresis loops and magnetization maps in the particles have been presented for each scenario. The potential applicability of the findings to the fabrication of memory storage devices has been discussed.

New paleomagnetic results from the Permian Emeishan basalts in the Zhaotong area, NE Yunnan province, China show four natural remanent magnetization components. Detailed stepwise thermal demagnetization of basaltic samples from 16 flows from the Dadi section, which represent basalt units III and IV, isolated two groups of characteristic remanent magnetizations. Samples in unit IV (five flows) record a southwest declination and a moderate downward inclination that is considered to be a partial remagnetized remanence. The bottom flows from unit III (11 flows) record a normal polarity direction, interpreted as a remagnetization, which yields a tilt-corrected mean direction of Ds/Is = 8.8°/31.6° (N = 9, ks = 39.7, α95 = 8.3°), with a corresponding paleomagnetic pole at 77.1°N, 240.0°E (K = 49.2, A95 = 7.4°). The secondary directions have steeper inclinations than primary ones that have been successfully recovered from other studies in this area of the Emeishan basalts. By comparison with the Phanerozoic paleomagnetic poles of the South China Block, the preferred timing of remagnetization is the Lower-Middle Jurassic. Field relationships suggest that the remagnetization of the Emeishan basalts is coeval with the spatially related, but localized, copper mineralization. Thus the timing of the main copper mineralization hosted in the Emeishan basalts is hypothesized to occur in the Early-Middle Jurassic.