Anisotropy Of Magnetic Susceptibility Research Articles

Unraveling tectonic inversion and wrench deformation in the Eastern Cordillera (Northern Andes) with paleomagnetic and AMS data

Complex orogenic belts typically display internal variations in deformational style, as is the case of the northern Eastern Cordillera of Colombia, which changed abruptly into a regional strike-slip system in the NNW-striking Santander Massif. We report paleomagnetic data, anisotropy of magnetic susceptibility (AMS) data, and magnetic mineralogy from 47 sites distributed in the northern Eastern Cordillera and Santander Massif to investigate and compare: (1) variations in the intensity of the deformation, (2) magnitude and sense of vertical axes rotations, and (3) the character and effect of strike-slip displacements along the Bucaramanga fault and NE-striking transverse faults within the Santander Massif. Rock magnetic experiments show that hematite is the principal magnetization carrier in all these rocks. Rocks of the axial zone of the Eastern Cordillera show intermediate magnetic fabrics. Magnetic fabrics of rocks from the Santander Massif, and the western flank of the Eastern Cordillera, are uniformly oblate with preservation of sedimentary fabrics. Directions of the ChRM from sites in the Eastern Cordillera (30 accepted of 35 sites) are interpreted to indicate that the axial zone has not been rotated, whereas sites located along the western flank of the northern Eastern Cordillera yield data suggesting clockwise rotations, which increase in magnitude up to 90° in areas bounded by NE-striking transverse faults. In the Santander Massif (9 accepted of 12 sites) data suggest a mix of counterclockwise rotations (~30°) and clockwise rotations of ~40°. The inferred clockwise vertical-axis rotations in the northern Eastern Cordillera and Santander Massif of up to 45° are interpreted to be related to tectonic inversion of pre-existing Mesozoic age normal faults during the Neogene as right-lateral faults. Our corrected paleomagnetic inclination data are interpreted to support the hypothesis of northward translation of the studied tectonic elements during the Middle Jurassic to earliest Cretaceous time.

Deformation of the colliding Luzon volcanic arc: Strain analysis using magnetic fabrics of syn-orogenic mudstones in the Coastal Range, eastern Taiwan

Exposed in the Coastal Range of eastern Taiwan is a portion of the Luzon volcanic arc that has collided with the South China continent since 6 Ma, as well as syn-orogenic sedimentary rocks deposited on the arc and subsequently intensely folded and thrusted. This study sampled syn-orogenic mudstones for the measurement of anisotropy of magnetic susceptibility (AMS) at four sites on the sides of the range. The AMS fabrics reveal a contribution from burial compaction and, less significantly, tectonic shortening which varies slightly across the range. This lateral variation is considered as, for simplicity, a result of two-phase deformation because these rocks were involved in an eastward propagating back thrust system on the colliding arc. A new strain analysis method is developed to estimate the overall tectonic strain by unstraining the pseudo-strains with respect to the AMS measurements at each site with the knowledge about the distribution of the susceptibility ellipsoids in the unstrained state. Strain results reveal that shortening phases occurred before and after the folding, with a shortening ratio of 0.177–0.195 and 0.181–0.248, respectively. The post-folding shortening on the western side is sub-parallel to the range, and the pre-folding shortening on both sides is layer-parallel and nearly perpendicular to the range. Therefore, the mudstones underwent layer-parallel shortening, fold-related tilting and eventually orogen-parallel shortening after deposition. This sheds light on the complexity in deformation of the colliding Luzon arc.

Cenozoic Uplift of Tanggula Range and Tuouohe Basin, Northern Tibet: Insights of the Anisotropy of Magnetic Susceptibility

The timing and intensity of deformation of the Tanggula Range and Tuotuohe Basin are in debatable but strengthening the research on them is necessary for better understanding the geodynamic models of the Tibet and the tectonic-climate connections during the Cenozoic. Here we present the anisotropy of magnetic susceptibility (AMS) records from the foreland Tuotuohe Basin to understand the tectonic uplift history of the Tanggula Range for the interval of ∼37–19.7 Ma. Rock magnetic analyses indicate that the main magnetic carrier is paramagnetic and the minor is hematite. Thus, the AMS in the Tuotuohe Section (TS) can be used to track the tectonic strain related to tectonic processes. The distribution direction of the maximum principle susceptibility (Kmax) is approximately NW–SE, which intersects at about 10°with the strike of the strata and is nearly parallel to the Tanggula thrust fault system, whereas the minimum principle susceptibility (Kmin) is oriented in the NE–SW direction with a girdle distribution. This is consistent with the sedimentary fabric imprinted by the NE–SW shortening direction, representing the earliest deformation stage. AMS data in the TS can be divided into two phases at 30 Ma. From ∼37 to 30 Ma, the AMS parameters indicate an active tectonic strain and the Tanggula Range uplift induced by the India–Asia convergence, whereas between 30 and 19.7 Ma, the strain is weak compared with the earlier phase. Finally, the weak strain environment between 30 and 19.7 Ma indicated by the AMS indexes of the TS and the paleoelevation evidence from the Tuotuohe Basin all together suggest that an additional 1000–2000 m of surface uplift of the basin may have begun after 19.7 Ma.

Anisotropy of Magnetic Susceptibility Reveals Late Miocene Tectonic Activity in the Western Qaidam Basin

The western Qaidam Basin on the northeastern Tibetan Plateau located at the intersection between the Altyn Tagh Fault and the Kunlun Fault/Qimen Tagh Fault holds significant potential to reveal the tectonic process of these two faults as well as the evolution of the Qaidam Basin. In this paper, we conducted detailed anisotropy of magnetic susceptibility (AMS) records from Late Cenozoic sediments at the Qigequan section in the western Qaidam Basin to shed new light on the tectonic processes in this region. Based on the distribution of three principal axes of magnetic fabrics as well as magnetic fabric parameters, the AMS records can be divided into three parts. The lower part (∼6.9–4.6 Ma), mainly made of fine-grained mudstone and siltstone, exhibits three well-grouped principal axes with a NE-SW elongated Kmin axis as the embryonic tectonic magnetic fabric, suggesting constant NE-SW compressional strain. The middle part (∼4.6–3.0 Ma), characterized by mudstone, siltstone and sandstone, shows three less grouped principal axes and suggests a relatively weak and stable tectonic environment. The three principal axes of the upper part (∼2.4–0.4 Ma) is composed of sandstone and conglomerate of the Qigequan Formation, similar to the middle part, which was primarily attributed to the coarse lithology and not sensitive to tectonics since ∼2.6 Ma. The NE-SW compressional strain in the western Qaidam Basin is consistent with that in the northeastern basin, both of which are parallel to the upper crust movements revealed by the GPS, suggesting the dominant NE-SW compressional strain in the western and northern basins in the late Cenozoic. The decreasing magnitude of tectonic activities during ∼6.9–4.6 Ma indicates that the major geological units released most of the compressional strain in the western Qaidam Basin during tectonic activity that initiated in the early-late Miocene.

Effect of magnetocrystalline anisotropy on magnetocaloric properties of an AlFe2B2 compound

It is well known that the temperature dependence of the effective magnetocrystalline anisotropy energy obeys the $l(l+1)/2$ power law of magnetization in the Callen-Callen theory. Therefore, according to the Callen-Callen theory, the magnetocrystalline anisotropy energy is assumed to be zero at the critical temperature where the magnetization is approximately zero. This study estimates the temperature dependence of the magnetocrystalline anisotropy energy by integrating the magnetization versus magnetic field ($M\ensuremath{-}H$) curves, and found that the magnetocrystalline anisotropy is still finite even above the Curie temperature in the uniaxial anisotropy, whereas this does not appear in the cubic anisotropy case. The origin is the fast reduction of the anisotropy field, which is the magnetic field required to saturate the magnetization along the hard axis, in the case of cubic anisotropy. Therefore, the magnetization anisotropy and anisotropic magnetic susceptibility, which are the key factors of magnetic anisotropy, could not be established in the case of cubic anisotropy. In addition, the effect of magnetocrystalline anisotropy on magnetocaloric properties, as the difference between the entropy change curves of ${\mathrm{AlFe}}_{2}{\mathrm{B}}_{2}$ appears above the Curie temperature, is in good agreement with a previous experimental study. This is proof of magnetic anisotropy at slightly above Curie temperature.

Upper Crustal Collapse Reconstructed the Topography and Remodeled the Fault System of the Chuandian Fragment in the Southeastern Edge of the Tibetan Plateau, Evidenced by Anisotropy of Magnetic Susceptibility Data Sets

AbstractThe steps of the southeastward stepwise‐descending topography of the Chuandian Fragment (CDF) in the southeastern edge of the Tibetan Plateau coincide with N‐S and NE‐SW trending faults that changed from thrusting to normal activity, indicating that since the Middle‐Late Miocene the CDF maintained an E‐W oriented extensional tectonic environment. However, the anisotropy of magnetic susceptibility (AMS) data sets presented herein, from the Cretaceous and Cenozoic sedimentary strata of the southeastern Tibetan Plateau and its edge, show that since ∼28.0 Ma the CDF remained within a stabilized compressional stress field, oriented NEE‐SWW. A comprehensive analysis of the AMS results, topography, fault systems, and geophysical observations indicate that the northward‐advancing eastern Himalaya syntaxis impeded the southeastward‐flowing viscous lower crust and correspondingly decreased its flux, which could have reduced the thickness of the lower crustal channel beneath the CDF. The original low‐gradient topography of the CDF formed by the viscous lower crustal flow could no longer be supported by the thinned lower crustal channel, and thus gravity drove the collapse of the uplifted CDF. This process reconstructed the topography and remodeled the preexisting fault systems of the CDF, resulting in the coexistence of the E‐W oriented extensional tectonic environment and the stabilized NEE‐SWW oriented compressional stress field of the western part of the CDF, since the Middle‐Late Miocene. Thus, the change in the status of the lower crustal channel related to block interactions provided a major geodynamic setting for shaping the topography of the southeastern edge of the Tibetan Plateau.

Enhancing the reliability of the magnetostratigraphic age assignment of azimuthally nonoriented drill cores by the integrated application of palaeomagnetic analysis, field tests, anisotropy of magnetic susceptibility, and the evolution of the endemic fauna as documented on the upper Miocene limnic deposits of the Turiec Basin (Western Carpathians)

Enhancing the reliability of the magnetostratigraphic age assignment of azimuthally nonoriented drill cores by the integrated application of palaeomagnetic analysis, field tests, anisotropy of magnetic susceptibility, and the evolution of the endemic fauna as documented on the upper Miocene limnic deposits of the Turiec Basin (Western Carpathians)

Imaging white matter microstructure with gradient-echo phase imaging: Is ex vivo imaging with formalin-fixed tissue a good approximation of the in vivo brain?

PurposeEx vivo imaging is a commonly used approach to investigate the biophysical mechanism of orientation‐dependent signal phase evolution in white matter. Yet, how phase measurements are influenced by the structural alteration in the tissue after formalin fixation is not fully understood. Here, we study the effects on magnetic susceptibility, microstructural compartmentalization, and chemical exchange measurement with a postmortem formalin‐fixed whole‐brain human tissue.MethodsA formalin‐fixed, postmortem human brain specimen was scanned with multiple orientations to the main magnetic field direction for robust bulk magnetic susceptibility measurement with conventional quantitative susceptibility imaging models. White matter samples were subsequently excised from the whole‐brain specimen and scanned in multiple rotations on an MRI scanner to measure the anisotropic magnetic susceptibility and microstructure‐related contributions in the signal phase and to validate the findings of the whole‐brain data.ResultsThe bulk isotropic magnetic susceptibility of ex vivo whole‐brain imaging is comparable to in vivo imaging, with noticeable enhanced nonsusceptibility contributions. The excised specimen experiment reveals that anisotropic magnetic susceptibility and compartmentalization phase effect were considerably reduced in the formalin‐fixed white matter specimens.ConclusionsFormalin‐fixed postmortem white matter exhibits comparable isotropic magnetic susceptibility to previous in vivo imaging findings. However, the measured phase and magnitude data of the fixed white matter tissue shows a significantly weaker orientation dependency and compartmentalization effect. Alternatives to formalin fixation are needed to better reproduce the in vivo microstructural effects in postmortem samples.

Insight into anisotropic magnetocaloric effect of CrI[formula omitted

CrI3 is considered to be a promising candidate for spintronic devices and data storage. We derived the Heisenberg Hamiltonian for CrI3 from density functional calculations using the Liechtenstein formula. Moreover, the Monte–Carlo simulations with the Sucksmith–Thompson method were performed to analyze the effect of magnetic anisotropy energy on the thermodynamic properties. Our method successfully reproduced the negative sign of isothermal magnetic entropy changes when a magnetic field was applied along the hard plane. We found that the temperature dependence of the magnetocrystalline anisotropy energy is not negligible at temperatures slightly above the Curie temperature. We clarified that the origin of this phenomenon is attributed to anisotropic magnetic susceptibility and magnetization anisotropy. The difference between the entropy change of the easy axis and the hard plane is proportional to the temperature dependence of the magnetic anisotropy energy, implying that the anisotropic entropy term is the main source of the temperature dependence of the free energy difference when magnetizing in a specific direction other than the easy axis. We also investigated the magnetic susceptibility that can be used for the characterization of the negative sign of the entropy change in the case of a hard plane. The competition of the magnetocrystalline anisotropy energy and external magnetic field at a low temperature and low magnetic field causes a high magnetic susceptibility as the magnetization fluctuates. Meanwhile, the anisotropy energy is suppressed as a sufficient magnetic field is applied along the hard axis, and the magnetization is fully rotated to the direction of the external magnetic field.

Understanding the maturity of columnar joints and its spatial relationship with eruptive centre: A critical appraisal from the Rajmahal basalt, India

We investigate the columnar joints of the Rajmahal Trap (India) in detail to understand the maturity with respect to its eruptive centre. The fabrics in the massive columnar basalt of the study area are investigated using Anisotropy of Magnetic Susceptibility (AMS) studies prior to the maturity analysis. Fabric analysis reveals that rocks are devoid of any tectonic deformation and the columnar structures that are observed in them are necessarily primary. The maturity analysis has been implemented using a number of maturity indices, such as Voronoi polygons, hexagonality index, uniformity in mean side length, mean area and mean internal angle of the polygons, and also by the distribution of the number of polygon sides. The Voronoi polygon analysis for Rajmahal Trap suggests that the diameter ratio ranges from 1.38 to 1.52, thus indicating the same maturity as Voronoi polygon sets. The hexagonality index depicts that the maturity increases away from the fissure point towards the periphery, where six sided columns with smaller area and side length are observed. It is found that as the maturity increases, column mean side length as well as column mean top area decreases, while average number of column sides increases. We envisaged that the difference between ambient and the magma temperature played an important role in controlling column maturity. Based on the overall maturity studies, we conclude that maturity of the columnar joint increases away from the eruptive centre, towards the peripheral part of the Rajmahal Trap.

Lithospheric thinning of the North China craton: Insights from Early Cretaceous intermediate–mafic dyke swarms in Jiaodong peninsula

The coupling/decoupling relationships between shallow crustal deformation and deep mantle tectono-magmatic activities, during lithospheric thinning and destruction of cratons, remain hotly debated in the last decades. Multidisciplinary studies were done on intermediate–mafic dyke swarms diffusively located in southern Jiaodong peninsula, southeastern North China craton (NCC) to explore the crustal and lithospheric mantle responses to regional tectonic extension. Uniform ages (122–121 Ma) of the dykes indicate intensive magma generation at the mantle depth around 122 Ma related to large-scale tectonic extension of regional lithospheric mantle. Systemic anisotropy of magnetic susceptibility (AMS), geochemical, and Sr-Nd isotope analyses suggest that the dykes were originated from enriched lithospheric mantle sources and emplaced along crustal fractures formed in a WNW-ESE oriented extensional stress field. We show that the Jiaodong lithosphere experienced two stages of Early Cretaceous tectonic evolution, i.e., an early stage (135–122 Ma) lithospheric thinning characterized by large-scale tectonic extension of the crust and limited magmatic activities of crustal sources, and a late stage (122–108 Ma) lithospheric root collapse dominated by intensive tectonic extension and magmatism in the lithospheric mantle level. The decoupling crust-mantle evolution during lithospheric thinning and destruction of the NCC is ascribed to continuous tectonic extension in WNW-ESE direction.

Magnetic birefringence of montmorillonite dispersion

Compared with unadulterated polymers, filler/polymer composites can exhibit superior properties. Modulating the orientation of montmorillonite (MMT) filler may maximize this filler’s properties in shape-anisotropic applications. We measured the magnetic birefringence of MMT dispersions in water with custom magnetic birefringence equipment and estimated the inherent birefringence and anisotropic magnetic susceptibility of MMT. We classified polydisperse MMT to prepare MMT dispersions with a narrow size distribution. From the relationship between the retardation obtained by magnetic birefringence measurements and the reciprocal of the square of the magnetic field, we estimated the inherent birefringence of MMT to be −0.060. Considering the size distribution, and by setting the anisotropic magnetic susceptibility to −1.5 × 10−5, we reproduced the magnetic flux density dependence of the magnetic birefringence of MMT with a particle size of ≤300 nm.

Magnetic fabric and geomorphic characteristic of Neotectonic activity along strike direction of North Almora Thrust, Kumaun Lesser Himalaya, India

Structurally, the North Almora Thrust (NAT), is placed in the northern proximity of the Almora Nappe (AN) in the Kumaun Lesser Himalaya. The NAT is characterized by the presence of a zone of mylonitic rocks of basal Saryu Formation (1800 ± 100 Ma) in the hanging wall and the metasedimentaries of Inner Lesser Himalayan rocks as the footwall block. The NAT has been dextrally offset by two estabilished major faults i.e. Saryu River Fault (SRF) in Saryu Valley and Dwarahat-Chaukhutia Fault (DCF) in Ramganga valley. In present study, we identified four new faults, based on field study, geomorphic landform and magnetic fabric analysis. These faults are N–S trending Pancheshwar Fault, NE–SW Rameshwer Fault, NNE-SSW trending Kosi Fault, and NNE-SSW trending Gagas Fault (GF). Our results show that the zone is bound by cross cutting relation with NAT and these fault zones are comparatively more active than other regions. Furthermore, we suggest that the steep and NW–SE orientation of magnetic foliation within the NAT zone is a result of NE–SW oriented progressive regional compression. The magnetic foliations represent the unseen internal foliations in the rocks developed due to preferred alignment of magnetic minerals and can be found through the Anisotropy of magnetic susceptibility (AMS) study. Variation in the alignment of the field and magnetic foliations are developed due to superimposed brittle deformation along the faults over the pre-existing field foliations. Magnetic foliations represent the impact of last stage deformation and significant to find brittle deformation and finite strain in the rocks of the study area. The lowering of anisotropy (Pj) away from the fault zone represents distribution of strain across the NAT zone. AMS fabric confirms the presence of faults developed across the NAT zone and also explains the deformation pattern along these faults. The geomorphic anomalies and steepness changes across the NAT zone are correlated with active deformation along the NAT and associated transverse faults.

Depth structure of the Gorishne-Plavninsk structure and general principles of geological and geophysical study of the Krivoy Rog-Kremenchug iron-ore strip

The article presents the results of the newest research performed by the State Enterprise «Ukrainian Geological Company» and the Institute of Geophysics of the National Academy of Sciences of Ukraine in 2021 to find out the morphology and elements of occurrence of an redeposit within the limits of the Gorishne-Plavninsk-Lavrikovsk area of the Krivoy Rog-Kremenchug iron-ore strip. In the process of geological and geophysical studies, a large body of new geological and geophysical data was obtained regarding the deep structural and morphological features of the construction of the Gorishne-Plavninsk structure (GPS), associated with the Krivoy-Rog deep fracture zone.
 Materials of reinterpretation of previously per formed ground-based magnetometric and gravimetric surveys, detailed high-altitude aeromagnetic studies and the study of the density and magnetic properties of the structure rocks, including the anisotropy of magnetic susceptibility using new equipment and techniques, gravimagnetic modeling with the construction of three-dimensional volume model of the structure lead to the conclusion that this structure is a typical drag fold with a pronounced reversal of its southern part by the right-hands hear. Its primary formation occurred as a faulted band of sedimentary-volcanogenic and extrusive formations of subvertical bedding and spreading to a depth of at least 1.5—2 km.
 A complete morphological and kinematic analogue of the GPS is the previously studied Likhmanovsk structure, located in the southern most part of the Krivoy Rog-Kremenchug strip. Many iron-ore structures of the Middle Bug area are close to it in structure and kinematics, the primary subvertical faulting and doubtful sedimentary genesis were mentioned earlier. All these data require a new approach to the study of iron-ore and some other deposits of the Ukrainian Shield associated with fault tectonics, as well as to the genesis problems and stratigraphy of rocks of the Early Precambrian.

Magnetic Fabrics and Petrography of Rocksalts Reveal Preferred Orientation of Anhydrites within a Halite Matrix

We investigate the magnetic fabrics and microstructures of diamagnetic rocksalt samples from the Sedom salt wall (diapir), Dead Sea Basin, as possible strain markers. A comprehensive study of anisotropy of magnetic susceptibility (AMS), combined with magnetic, microtextural, geochemical and mineralogical analyses allows us to depict the deformation mechanisms and to reveal the mineral sources of the AMS. The rocksalts are composed of halite as the major mineral phase (>80%) and anhydrite as a minor phase (5–20%), and have an average magnetic susceptibility value of −13.4 ± 0.7 × 10−6 SI. Ferromagnetic and paramagnetic minerals make a negligible contribution to the bulk magnetic properties of the samples. The AMS indicates and reveals significant anisotropy with the maximum susceptibility axis (K1) subparallel to the bedding strike, although the cubic halite crystals are isotropic. Polarizing microscope and SEM images show preferred alignment of needle-like anhydrite crystals parallel to the direction of the K1 axis. Petrographic investigation of gamma irradiated thin sections reveals the deformation recorded in the microstructures of the rocksalts and points to a dominant contribution by dislocation creep, although both dislocation creep and pressure solution were active deformation mechanisms. We infer that during dislocation creep, the thin bands of anhydrite crystals deform along with the surrounding halite grains. We suggest that although the shape preferred orientation of halite grains is not indicative of finite strain because of resetting by grain boundary migration, the preferred orientation of the anhydrite crystals may be. These results suggest that the AMS of the rocksalts provides a textural proxy that reflects deformation processes of the rocksalts, despite their very low magnetic susceptibility.

Paramagnetic Chemical Probes for Studying Biological Macromolecules.

Paramagnetic chemical probes have been used in electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopy for more than four decades. Recent years witnessed a great increase in the variety of probes for the study of biological macromolecules (proteins, nucleic acids, and oligosaccharides). This Review aims to provide a comprehensive overview of the existing paramagnetic chemical probes, including chemical synthetic approaches, functional properties, and selected applications. Recent developments have seen, in particular, a rapid expansion of the range of lanthanoid probes with anisotropic magnetic susceptibilities for the generation of structural restraints based on residual dipolar couplings and pseudocontact shifts in solution and solid state NMR spectroscopy, mostly for protein studies. Also many new isotropic paramagnetic probes, suitable for NMR measurements of paramagnetic relaxation enhancements, as well as EPR spectroscopic studies (in particular double resonance techniques) have been developed and employed to investigate biological macromolecules. Notwithstanding the large number of reported probes, only few have found broad application and further development of probes for dedicated applications is foreseen.

Differentiating between remote and local strain fields near mesoscale faults by magnetic fabrics in deformed chalks

Characterizing the strain field near faults is a key to understanding its formation origin, kinematics and mechanism. We use magnetic fabrics and Anisotropy of Magnetic Susceptibility (AMS) as strain markers to study the development of the strain field near mesoscale normal faults cutting a weakly deformed chalk host rock that crops out in the Beer Sheva syncline, Israel. We provide a high-resolution view of the magnetic fabrics by constructing horizontal cross-sections, from distance of <0.2 m up to ∼20 m from the fault planes. The results indicate deformation fabrics that are controlled by the orientation-distribution of calcite coccolith in the chalk. The AMS axes indicate similar and consistent orientations at all localities, even though adjacent faults have different orientations, indicating that the strain field did not develop as a result of the slip along the faults. The maximum susceptibility axes (K1) and the intermediate susceptibility axes (K2) axes are parallel and perpendicular to the syncline axis, respectively. These relations suggest that the magnetic fabrics had already been acquired before of the faults and represent the remote strain field that was operating during the formation of the Beer Sheva syncline. We provide independent arguments for an aseismic slip origin of the studied faults, and, by comparing the results with magnetic fabrics near co-seismic faults that formed under similar sedimentary conditions, we highlight the possibility that aseismic and seismic faults have different impact on the distribution of magnetic fabrics and inelastic deformation near them.

Magnetic fabrics as strain markers in folded soft-sediment layers

We exploit the potential of magnetic fabrics acting as strain markers in folded layers, by analysing an exceptionally well-exposed, recent (<1 kyr) slump horizon in unlithified lake deposits within the Dead Sea basin. The ∼3-m-long folded soft-sediment layer, together with an underlying basal detachment, and an ‘undeformed’ reference layer are extensively sampled (n = 97) for an anisotropy of magnetic susceptibility (AMS) analysis. This analysis reveals deformation fabrics within the folded layer which are significantly different from fabrics detected in the ‘undeformed’ layer. The maximum magnetic susceptibility axes (K1) show a hinge-parallel orientation, and the minimum magnetic susceptibility axes (K3) show a trail of orientations directed eastward parallel to the direction of downslope slumping toward the depocenter of the basin. In terms of shape of the AMS, samples from the ‘undeformed’ layer are oblate, while the majority of samples from the fold backlimb are oblate to neutral, and those from the forelimb and hinge zones are more prolate. We postulate that the deformation shown by the AMS analysis approximates well to sections through the strain ellipsoid in the folded layer, suggesting that magnetic fabrics serve as strain markers that are invisible to the naked eye. The deformation fabrics are created by particles moving relative to one another and reorganising during hydroplastic deformation. Particles physically rotate in the hinge zone, resulting in shortening of the intermediate axes and creation of more prolate shapes. The combination of two types of fabrics (deposition and deformation) in the hinge zones increases the intensity of the lineation due to the intersection of the primary and secondary fabrics (foliations). Based on the dense sampling scheme, we produce GIS-based interpolation maps that show the spatial distribution of the AMS parameters in the folded layer. These maps are compared to data from classical strain analyses, providing a benchmark for combining traditional structural methods and AMS analyses in studying folding and soft-sediment deformation.

Middle Ordovician bottom current deposits in the western margin of the North China craton: Evidence from sedimentary and magnetic fabrics

AbstractIn many modern deep‐water slope environments, deposits formed by bottom currents (contourites) are rather common. However, reports on ancient contourites in deep‐water environments are scarce and most of them remain contentious. Based on the study of high‐resolution sedimentological, sedimentary geological and magnetic fabric characteristics, this study presents the key evidence of bottom current activity in the Middle Ordovician Kelimoli Formation from the western margin of the North China craton, and reconstructs the deep‐sea circulation pattern and the direction of deep‐water bottom currents in the middle and low latitudes during the Middle Ordovician. Six typical carbonate microfacies are identified in the Kelimoli Formation, which can be grouped into three sedimentary facies types related to the main interpreted depositional processes (bottom current, undifferentiated bottom current and hemipelagic settling, and hemipelagic settling). The evidence of bottom current deposits are five‐fold. Firstly, it is possible to observe a variety of traction current structures, which mainly represent bed‐load‐dominated transport of sediments. Secondly, there are multi‐scale inverse grading and bi‐grading, as well as inversely‐graded and normally‐graded sedimentary sequences, which reflect the periodic change of bottom current activity. Thirdly, gradual or sharp contact boundaries and small internal erosional surfaces indicate omission surfaces caused by the oscillating variation of bottom current velocity. Fourthly, the continuous rhythmic change of sedimentary fabrics on the microscopic scale reflects sustained, waxing and waning current intensities. Fifthly, the anisotropy of magnetic susceptibility reveals the microscopic fabric characteristics of imbricated magnetic grains, which represent the continuous action of directional current, and the restored palaeocurrent direction indicates that the current is mainly parallel to the slope strike. After the palaeo‐north correction of the North China craton clockwise rotation of 120° to 150° since the Ordovician, anisotropy of magnetic susceptibility shows that the direction of bottom current in the study area is towards the north‐east/east. Therefore, it is speculated that there was a clockwise deep‐water circulation in the middle and low latitudes of the southern hemisphere during the Ordovician. This study not only provides sedimentological evidence for the Ordovician bottom current activity, but also contributes to a better understanding of the Ordovician palaeoceanographical environment, especially the Middle Ordovician deep‐sea circulation pattern.

Localising individual atoms of tryptophan side chains in the metallo-β-lactamase IMP-1 by pseudocontact shifts from paramagnetic lanthanoid tags at multiple sites.

The metallo--lactamase IMP-1 features a flexible loop near the active site that assumes different conformations in single crystal structures, which may assist in substrate binding and enzymatic activity. To probe the position of this loop, we labelled the tryptophan residues of IMP-1 with 7-C-indole and the protein with lanthanoid tags at three different sites. The magnetic susceptibility anisotropy () tensors were determined by measuring pseudocontact shifts (PCSs) of backbone amide protons. The tensors were subsequently used to identify the atomic coordinates of the tryptophan side chains in the protein. The PCSs were sufficient to determine the location of Trp28, which is in the active site loop targeted by our experiments, with high accuracy. Its average atomic coordinates showed barely significant changes in response to the inhibitor captopril. It was found that localisation spaces could be defined with better accuracy by including only the PCSs of a single paramagnetic lanthanoid ion for each tag and tagging site. The effect was attributed to the shallow angle with which PCS isosurfaces tend to intersect if generated by tags and tagging sites that are identical except for the paramagnetic lanthanoid ion.