Anisotropy Of Magnetic Susceptibility Research Articles

Magnetic shape fabric analysis from syntectonic granites: a study based on the eigenvalue method

AbstractWe investigate the shape and strength of the magnetic fabrics (anisotropy of magnetic susceptibility (AMS) data) of various massive granitic plutons from different parts of India, using the eigenvalue method. The study aims to analyse eigenvalues and establish their relationship with various deformational attributes. It involves: (1) calculating eigenvectors and their corresponding eigenvalues from magnetic fabric datasets; (2) finding a link between the geometrical appearance of eigenvectors and the mechanistic issues involved with a specific deformation scenario; and (3) determining shape and strength parameters from the magnetic foliation data distribution.The statistical analysis for the unimodal magnetic fabric dataset of orthorhombic symmetry class implies that the plane, consisting of intermediate (V2) and minimum (V3) eigenvectors with pole V1, accurately traces the instantaneous stretching axis (ISAmax) of a particular material flow system under a pure shear regime. Moreover, for the distributions of similar symmetry and modality, we infer that the rotational characteristics of eigenvectors with respect to a fixed coordinate cause a distinct shift of such planes (V2–V3) from the ISAmax of a steady-state flow system under simple shear, where a substantial amount of rotational strain is involved. However, our findings also suggest that variation in symmetry and modality of magnetic fabric data distribution of different studied granitoids can directly influence the relative disposition of V2–V3 with respect to the direction of ISAmax. We conclude that eigenvalue analysis of magnetic fabrics is a powerful approach, which can be utilized while studying the salient deformational aspects of any syntectonic massive granitic body.

Factors affecting thickness and frequency of turbidites triggered by earthquakes in Kumburgaz Basin, Sea of Marmara

Submerged fault ruptures generate earthquake-triggered mass flow deposits, which are extensively used as a tool in subaqueous paleoseismology. In tectonically active deep sedimentary basins, such as the Sea of Marmara (SoM), these mass flow deposits are defined as turbidite-homogenite units (THUs), consisting essentially of a coarse basal part and an overlying homogeneous mud (homogenite). Detailed characterization of THUs is crucial in order to establish meaningful criteria to link these units with earthquakes events and to identify their transport routes and depositional mechanisms. Here, we combine μ-X-ray Fluorescence (μ-XRF), Anisotropy of Magnetic Susceptibility (AMS) and additional rock magnetism analyses of a 21-m long piston core from the Kumburgaz Basin of SoM to define the upper stratigraphic boundary of THUs with hemipelagic sediments and investigate the controls of hydrological changes on turbidite frequency and thickness over the last 15 kyrs BP. The sedimentary succession of this period includes a lower lacustrine and an upper marine unit with two Holocene sapropel intervals. The sequence is interrupted by a total of 70 THUs, characterized by a significant magnetic foliation related to the depositional setting rather than the magnetic signature. Magnetic mineralogy of the coarse basal parts of THUs have more ferromagnetic particles than the overlying homogenites and background sediments. While the homogenite parts have a more constant mineralogy than the basal parts, they do not differ the background sediments.Based on an event-free chronostratigraphic model derived from radiocarbon ages and the published age of lacustrine-marine (L-M) transition, the average THU occurrence intervals in the lacustrine (14.8–12.6 kyrs BP), lower sapropel (11.2–5.7 kyrs BP), upper sapropel (5.4–2.7 kyrs BP) and non-sapropelic part of the marine unit (2.7 kyrs BP-present) are 235 yrs., 287 yrs., 114 yrs. and 160 yrs. respectively. The average thickness of the THUs in the same units are 20.8 cm, 15.7 cm, 6.1 cm and 6.1 cm. The variability of average THU occurrence intervals and THU thicknesses are controlled by the sea level rise and salinity increase following the full marine connection of the SoM at 12.6 kyrs BP, which caused changes in slope stability, sediment composition and sediment deposition in different parts of the basin. Geomechanical properties of the lower sapropel appears to have been important in resulting long THU recurrence intervals and relatively high THU thicknesses.

When did the large-scale extensional tectonics begin in North China Craton?

In response to the craton destruction, the North China Craton (NCC) underwent the Early Cretaceous extensional tectonics. During this period, the eastern NCC has also experienced numerous plutonism, volcanism, and extensional structures. Particularly, half-graben or graben, Early Cretaceous extensional domes, metamorphic core complex, and syn-kinematic plutons are widespread throughout the NCC and its surrounding area, with a peaking age of 125 Ma, pointing to a large-scale severe NW-SE extension. However, it remains unknown when and how the large-scale extension is initiated. To answer this key issue, we choose two plutons (Fengjiayu-Xibailianyu and Gubeikou plutons) with the age of early stage of the Early Cretaceous (130–127 Ma) as the target of this study. The Fengjiayu-Xibailianyu pluton is close to, while the Gubeikou pluton is far away from the Early Cretaceous intensive extensional region. A multidisciplinary study, including structural geology, anisotropy of magnetic susceptibility (AMS), and gravity modeling, has been carried out on these two plutons to reveal the tectonic regime coeval with their emplacement. Both of these two plutons share similar features of concentric magnetic foliations and variable magnetic lineations which are decoupled with the ductile fabric in their country rocks. Accordingly, we considered that they intruded in a permissive way at a weak extension regime during the Early Cretaceous (130–127 Ma), just before the Late Mesozoic peak of the magma flare-up and large-scale extensional tectonics of the NCC. Combined with our previous works, the Early Cretaceous NW-SE trending extension in NCC was further subdivided into the early-stage weak extension during 130–127 Ma and the late-stage intensive extension during 127–110 Ma, namely the large-scale extension initiated after 127 Ma. The early-stage extension could be ascribed to the westward subduction of the Izanagi plate under the Eurasian continent.

Unraveling the complex burial history of the Antrim formation in Michigan basin using paleomagnetism, rock magnetism and geochemistry

This paper presents an integrated paleomagnetic, rock magnetic and geochemical study of the Devonian Antrim shale in the Michigan Basin. Specimens were obtained from two unoriented vertical cores (named St. Chester and Krocker) and sampled relative to a master specimen orientation line. Alternating field (AF) demagnetization experiments isolated a lower coercivity component (LC) from 0 to ∼60 mT in the Krocker core and corresponds to a Jurassic (170 Ma ± 25) magnetization. Higher coercivity components (HC) in the Krocker core are unblocked from ∼60 to 120 mT and unlike LC components, occasionally exhibit stable unblocking temperature ranges (e.g., 150–450°C) and higher AF demagnetization ranges (∼60–120 mT). HC components in the Krocker core are unique to certain members within the Antrim shale with a poorly resolved Middle Permian/Late Triassic magnetization in the Paxton member and Late Pennsylvanian (305 Ma ± 10) component in the Norwood. The St. Chester well exhibited a LC component among all specimens with a slightly older (205 Ma ± 10) than the Krocker core. Rock magnetic parameters indicate the magnetization resides in PSD/SD magnetite in both HC and LC components. Overall, the magnetizations are interpreted to be chemical remanent magnetizations (CRMs) with the HC component residing in SD magnetite which formed during hydrothermal activity in both cores. The LC component likely resides in PSD/MD magnetite and is interpreted to have formed in response to fluid flow associated with tectonic uplift and/or hydrocarbon migration. Petrographic observations indicate mineral assemblages consistent with hydrothermal mineralization (e.g., baroque dolomite). Depleted δ18O data from carbonate fractures are consistent with a hydrothermal fluid magnetization mechanism. Consistent anisotropy of magnetic susceptibility (AMS) lineations indicates either a long-lived paleocurrent direction or far-field tectonic shortening originating from the neighboring Acadian orogeny. Inorganic geochemistry indicate that paramagnetic Fe-rich clays carry the AMS signal. Lastly, an evaluation of the origin of chalcopyrite and monazite is performed through provenance analysis. These minerals are attributed to hydrothermal mineralization however, strong evidence suggests that some fraction of these grains were sourced from the Michigan Peninsula.

Rock magnetism and AMS studies in Kondapalle-Pangidi layered complex, Eastern Ghats Belt, India: Remanence carriers and tectonic implications

The present study is an integrated approach towards the rock magnetism and Anisotropy of Magnetic Susceptibility (AMS) of the high-grade metamorphic rocks in the Kondapalle Pangidi Layered Complex (KPLC), Eastern Ghats Belt (EGB), India. Our study aims at determining the petrography, rock magnetic properties and the magnetic fabrics. The rock magnetic properties and the magnetic fabrics from AMS studies are used to determine their tectonic implications. Petrography reveals that the chief remanence carrier mineral is Ti-magnetite. Rock magnetic studies including Isothermal Remanent Magnetization (IRM), back-field IRM, hysteresis loop studies, and thermo-magnetic studies reveals the same. The magnetic hysteresis parameters (remanence and coercivity) are used to determine the magnetic domains from a modified Day plot. The magnetic domains lie within Stable Single Domain and Pseudo Single Domain ranges, thereby explaining their potential to record an ancient magnetic field. Besides the ferrimagnetic remanence carriers, paramagnetic silicates are also dominant which controlled the development of magnetic fabric. The magnetic fabric bears analogy with the regional structures and bear tectonic implications related to the post-rifting closure of the ocean followed by subduction of the ocean basin, accretionary orogeny and felsic magmatism in the Indo-Antarctic continental blocks.

Splitting a large pluton by Cretaceous crustal extension: Evolution of the Ziyuan Detachment and crustal thinning of the South China Block

The Cretaceous extensional province of the South China Block (SCB), and the decratonization-induced extension in the North China Block (NCB), were both controlled by the Late Mesozoic subduction of the Izanagi/Paleo-Pacific Plate. Different from the metamorphic core complexes exhuming deep crustal rocks of the NCB, extension of the SCB is expressed by numerous half-graben basins and detachment of upper-middle crustal rocks, but its mode and mechanism remain unclarified. At the westernmost of this extensional province, the Early Paleozoic Yuechengling-Miao'ershan Massif, composed of the ductilely deformed Yuechengling pluton and undeformed Miao'ershan pluton, records Late Mesozoic detachment and exhumation. Magnetic fabrics of the western Yuechengling pluton are consistent with structural fabrics, while the NE-SW trending magnetic lineation and NE-SW striking magnetic foliation of the Miao'ershan pluton and the undeformed Yuechengling pluton reflect a pre-existing magma flow structure. Integrating our structural observation, anisotropy of magnetic susceptibility (AMS) results with gravity modeling, we reveal the deep geometry of the extensional dome and restore the original structure before the Late Mesozoic Ziyuan detachment. The mode of extension argues for a single batholith split into two separate massifs, thinning the crust of the central SCB. The shallow-dipping Ziyuan detachment fault (10°-30°) may account for the large horizontal extension but low exhumation of mid-crustal rocks in the SCB, in contrast to the large exhumation of deep crustal rocks in the NCB.

Latest Triassic and Late Jurassic extensional tectonics of the Sulu UHP orogenic belt, East China: Evidence from geological and geophysical data

To understand the post-orogenic tectonics related to collision between the North China Craton (NCC) and the South China Block (SCB), the Northern Sulu massif is a representative area. It experienced a complex evolution marked by exhumation of ultra-high-pressure metamorphism rocks, migmatization, and alkaline magmatism in the Latest Triassic, and felsic magmatism in the Late Jurassic. In this contribution, we carried out a combined study including structural analysis, anisotropy of magnetic susceptibility (AMS), and gravity survey on the Northern Sulu massif. According to our structural analysis, it is interpreted as an extensional dome, exhibiting dominantly SE-dipping foliations in its east and center and NW-dipping ones closer to its northwestern margin, NW-SE mineral and stretching lineations, and top-to-the-NW kinematics. The Latest Triassic pyroxene syenite has dominantly SE-dipping mesoscopic/magnetic foliations, NW-SE magnetic lineations, and wedge shape at depth, and the Latest Triassic quartz syenite has variable magnetic fabric. Considering geometric relations of plutons and country rocks, the former is a “syn-kinematic” pluton, while the latter post-dates the regional tectonics, constraining the timing of the top-to-the-NW shearing at 220–210 Ma. Compared with the syn-orogenic tectonic events, the Latest Triassic ductile deformation points to a NW-SE extension related to lithospheric delamination. Late Jurassic isotropic monzogranite is characterized by “onion-skin” magnetic foliations with NE-SW trending magnetic lineations, and NE- or SW-ward decrease of thickness at depth. On the basis of regional understanding, we link its emplacement with the Late Jurassic NE-SW extensional tectonics attributed to the oblique subduction of the Paleo-Pacific plate. Such two episodes of crustal extensions with magmatism reformed the crustal architecture of the SE-margin of the NCC, which considerably facilitated stress-transmission from plate-boundary to intraplate during the development of subsequent Late Mesozoic intracontinental deformations.

Magnetic Fabric Signature Within a Thrust Imbricate; an Analog Modeling Approach

AbstractIn this study, we report results from three analog models with a similar initial setup and different amounts of bulk shortening, to simulate the development of a thrust imbricate in fold‐and‐thrust belts at different stages. Samples are taken at the back‐ and forethrusts, in the complex forekink zones, and at random distances to thrusts for analysis using anisotropy of magnetic susceptibility as strain indicator. This analysis shows that three distinct types of magnetic fabric can be identified throughout the models: (a) a compactional oblate fabric that changes as a function of distance toward a localized deformation zone (e.g., thrust or kinkzone), (b) a thrust‐induced fabric with magnetic foliation parallel to the thrust surface depicting its geometry, and (c) a complex forekink zone fabric with broad girdle distributions of principal axes and magnetic lineation perpendicular to the shortening direction. The latter indicates an interplay between folding and thrusting of the shortened sand layers. Additionally, a decrease in the degree of anisotropy with appearance of a quantitatively more prolate fabric can be observed toward the thrusts and kinkzones. Moreover, a thrust‐induced fabric is inherited by the variation of strain, depicted by changes in magnetic fabrics. In conclusion, our analysis of model results shows that strain changes as a function of distance toward localized deformation zones with characteristic magnetic fabrics that develop as deformation continues.

Magnetic fabric of deformed Quaternary sediments: contributions to the understanding of the neotectonic activity in the surroundings of the Aburrá Valley, Central Cordillera, Colombia

The origin of the Aburrá Valley (AV) is proposed as a set of coalescent tectonic subbasins located along the northern portion of the Central Cordillera of Colombia, the Northern Andes of Colombia. The Itagüí, Medellín, Bello, and Barbosa subbasins have developed between the Romeral Shear Zone (RSZ) and the Antioqueño Batholith starting in the Late Cenozoic. The aim of this study is to contribute to the understanding of the AV neotectonic framework using the anisotropy of magnetic susceptibility (AMS) and structural analysis. For this, we measure the magnetic fabric ellipsoid shape of faulted sediments and compare them with the geometry and kinematics of fault planes to determine their relationship with the present-day stress field and the regional fault architecture. The principal directions of the elongation axes along the La Brizuela and Yarumalito sites were NE-SW, following the magnetic lineation trend and marking a normal displacement with a dextral component. A marked NW-SE magnetic cleavage was found for the La Caimana site along a strike-slip tectonic setting. Holocene ruptures of the principal displacement zone (i.e., the RSZ) and their surroundings, may indicate normal faulting, with fault bends and steps over basins controlled primarily by R´ and P structures. Moreover, the active faults located to the east of the AV indicate post Plio-Pleistocene deformations with normal faulting through 90/80 to 150/70 antithetic faults. This work identifies the AMS technique as a powerful tool, for understanding the neotectonic framework along urban and surrounding areas.

Paleomagnetism and Rock Magnetism of Permian sedimentary rocks and Early Jurassic Karoo (Large Igneous Province) sills intersected in the KWV-1 borecore, Eastern Cape Province, South Africa

The nearly 100 Ma record of almost continuous shallow marine to non-marine sedimentation from the Late Carboniferous to the Early Jurassic recorded in the Karoo Basin, South Africa, includes coal deposits and potentially significant shale gas occurrences. As such, numerous studies have addressed the thermal history of the Karoo Basin, using a range of approaches. We use paleomagnetic and rock magnetic data to evaluate the paleotemperature history of the host Permian strata (Ecca Group and lowermost Beaufort Group) intersected in the ∼2320 m deep KARIN KWV -1 drilling project core, obtained in 2015. Where cored, the Karoo sedimentary sequence has been intruded by several Early Jurassic mafic sills, belonging to the Karoo Large Igneous Province, of thickness ranging from less than 10 cm to ∼150 m. The continuous core provides a unique natural laboratory for studying the effects of Karoo magmatism on the basin's sedimentary sequence. The KWV-1 drilling project was spudded ∼10 km east of Willowvale town, Eastern Cape Province.The spatial variation in thermal effects in host sedimentary strata, relative to proximity to Karoo sill contacts, is well-defined on the basis of anisotropy of magnetic susceptibility (AMS) data, paleomagnetic demagnetization response, and thermal alteration index (A40) values based on temperature vs. magnetic susceptibility tests. A zone of pervasive remagnetization of host sedimentary strata characterizes the contact aureoles, the spatial extents of which are to a first order dictated by the thickness of each Karoo sill. A40 data are interpreted to show that ambient paleotemperature estimates increase from ∼150 °C in lower Beaufort/upper Ecca strata to ∼285° in Lower Ecca strata that are sufficiently removed from Karoo sills. However, lower Ecca Group rocks in close proximity to Karoo sills were likely heated to ∼500 °C. Natural remanent magnetization (NRM) intensities of rocks in proximity to sills range from ∼17 to ∼ 438 mA/m, and susceptibilities range from 1.3 to 3.2 × 10−3 SI volume. In contrast, for strata sampled at distances greater than the width of the nearest sill, NRM intensities range from 0.056 to ∼4 mA/m, and susceptibility values range between 193 and 488 X 10−6 SI volume. For host sedimentary rocks, remanence is completely unblocked at temperatures ranging from ∼350 °C to ∼630 °C and acquisition and backfield DC demagnetization of isothermal remanent magnetization (IRM) indicate that specimens are fully saturated in fields of ∼200–600 mT, with coercivity of remanence of ∼30–100 mT. All of the eleven Karoo sills examined in this study yield remanence inclinations that are moderate to steep negative, and are inferred to have recorded a normal polarity field, possibly during a single chron. Our results are interpreted to suggest that substantial thermal effects of Karoo sills on the host sedimentary strata are largely confined to the contact aureoles, with a width that is dependent on sill thickness. We hypothesize that parts of the Ecca sedimentary sequence have remained at ambient, basinal burial temperatures below about 150 °C, and thus that an early-acquired Permian remanence may possibly be preserved in these sedimentary rocks at sufficient distance from thermal contact aureoles. Alternatively, much of the sedimentary section may have been subject to a combination of thermoviscous/chemical remagnetization.

Criteria to identify sedimentary sills intruded during deformation of lacustrine sequences

Although sedimentary dykes have been widely reported across a range of settings, sedimentary sills have received somewhat less attention, perhaps due to the potential difficulties in identifying largely conformable intrusions within bedded sequences. Most outcrop descriptions of clastic intrusions are based on deep-water marine sequences, with few descriptions of sills in lacustrine settings. The recognition of sills in such settings is, however, important because lacustrine sequences are increasingly used as a record of palaeoseismic activity. The misidentification of sills that contain fragments and clasts of host stratigraphy with seismically-generated turbidites and debris flows, may lead to incorrect interpretations of palaeoseismicity. We use the Late Pleistocene Lisan Formation of the Dead Sea Basin as a case study, where laminated lake sediments preserve intricate relationships with sills. This permits us to not only establish a range of criteria used in the identification of sedimentary sills, but also examine relationships with adjacent seismically-triggered slumps and slides. Key criteria we use to recognise sills include marked changes in their thickness together with bifurcation and bridging geometries. Sills may be internally layered, contain lenses of breccia, together with aligned and folded clasts that may be truncated across upper sill contacts. Critical evidence for the interpretation of sills is also preserved along sharp but irregular upper contacts that erode and truncate bedding in the overlying host sequence. Minor apophyses and ‘wedges’ intrude both upwards and downwards from sills, while isoclinal recumbent ‘peel-back’ folds are created in host sediments by shear generated along the lower contacts of sills. We have undertaken anisotropy of magnetic susceptibility (AMS) analysis and find an oblate fabric that suggests flow and intrusion of sills along the strike of the slope, that may also help with their identification in bedded sequences. Sills form along detachments to both extensional and contractional deformation associated with seismically-generated slumps and mass transport deposits, together with sub-surface fold and thrust systems. High fluid pressures associated with injection of sedimentary sills may facilitate near-surface failure and downslope movement of the sedimentary pile.

Reconstruction of ancient volcanic complexes using magnetic signature: A case study from Cambrian andesite lava flow, Bohemian Massif

Reconstruction of the Upper Cambrian Křivoklát-Rokycany Volcanic Complex was made using anisotropy of magnetic susceptibility (AMS). The correlation of AMS with visible structures at a few sites showed that the most important and reliable information was the direction of magnetic lineation K1 that determines the direction of a lava flow. The analysis of K1 directions together with radially propagating dikes helped to determine the feeding area along the NW rim of the volcanic complex. One andesite feeder and one rhyodacite feeder were recognized with certainty. In addition, K1 directions pointed to a suspicious area with the presence of another andesite feeder in a caldera-like structure. The evaluation of data strongly suggests that magnetic susceptibility in andesite lavas increases with the distance from the feeder and also with the distance towards the upper part of the andesitic lava flow. We suggest that this might be related to the degree of oxidation of the lava flow before solidification as a reaction with oxygen in the atmosphere. Oxygen can react with FeO in the andesite melt, which consequently results in the formation of magnetite.

Composition and magnetic properties of rocks of Zarechenskaya and Nikolskaya magnetic anomalies (East coast of Lake Baikal)

The mineral composition of rock samples of the Zarechenskaya and Nikolskaya magnetic anomalies was determined. The mineral composition was compared with the magnetic properties of rocks, such as inductive and remanent magnetization, Curie temperature, anisotropy of magnetic susceptibility, and the Koenigsberg factor. The influence of the mineral composition on the magnetic properties of rocks is considered. This, in turn, will further increase the reliability of the interpretation of the results of tectonomagnetic monitoring performed here.

Time relationship between emplacement, fabric development and regional deformation of the Manchi granitic pluton (western - Cameroon domain)-an integrated AMS, CPO and microstructural investigation

In this study, we integrate anisotropy of magnetic susceptibility (AMS) and microstructural data including quartz crystallographic preferred orientation (CPO) from SEM-EBSD from the Manchi Pan-African granitic pluton with the objective of deciphering the time relationship between fabric development, emplacement and regional tectonics. The Manchi pluton, located in the western Cameroon domain of the Pan-African Fold Belt of Central Africa in Cameroon, is made of hornblende-biotite granite (HBtG), biotite granite (BtG) and protomylonites of HBtG. The pluton intruded the high grade country rocks made of banded gneiss and amphibolites. AMS of the pluton is controlled dominantly by paramagnetic phases such as, Fe-bearing silicates (biotite and hornblende). This is inferred from the low Km values (<500 × 10−6 SI units) as well as from hysteresis data. The AMS ellipsoid shape is mostly oblate, implying that flattening component of the strain was important during granite emplacement. Microstructural observations reveal presence of magmatic to sub-magmatic and solid-state deformation textures developed at moderate- to low-temperatures. This is consistent with the presence of rhomb <a> and basal <a> slip systems established from quartz c-axis data through EBSD analysis. The pluton recorded top-toward SW to top-toward south sense of shear as established by the kinematic markers. This indicates a component of simple shear during tectonic evolution of the pluton. We infer that the magnetic fabrics recorded in the Manchi granitic pluton is a manifestation of the D2 regional deformation. The dominance of flattening strain and the concentric pattern of magnetic data are indicative of ballooning being an important mechanism under transpressive regime.

Half-integer-spin quadrupolar nuclei in magic-angle spinning paramagnetic NMR: The case of NaMnO2

A combination of solid-state NMR methods for the extraction of 23Na shift and quadrupolar parameters in the as-synthesized, structurally complex NaMnO2 Na-ion cathode material, under magic-angle spinning (MAS) is presented. We show that the integration of the Magic-Angle Turning experiment with Rotor-Assisted Population transfer (RAPT) can be used both to identify shifts and to extract a range of magnitudes for their quadrupolar couplings. We also demonstrate the applicability of the two-dimensional one pulse (TOP) based double-sheared Satellite Transition Magic-Angle Spinning (TOP-STMAS) showing how it can yield a spectrum with separated shift and second-order quadrupolar anisotropies, which in turn can be used to analyze a quadrupolar lineshape free of anisotropic bulk magnetic susceptibility (ABMS) induced shift dispersion and determine both isotropic shift and quadrupolar products. Combining all these experiments, the shift and quadrupolar parameters for all observed Na environments were extracted and yielded excellent agreement with the density functional theory (DFT) based models that were reported in previous literature. We expect these methods to open the door for new possibilities for solid-state NMR to probe half-integer quadrupolar nuclei in paramagnetic materials and other systems exhibiting large shift dispersion.

Localising nuclear spins by pseudocontact shifts from a single tagging site.

Ligating a protein at a specific site with a tag molecule containing a paramagnetic metal ion provides a versatile way of generating pseudocontact shifts (PCSs) in nuclear magnetic resonance (NMR) spectra. PCSs can be observed for nuclear spins far from the tagging site, and PCSs generated from multiple tagging sites have been shown to enable highly accurate structure determinations at specific sites of interest, even when using flexible tags, provided the fitted effective magnetic susceptibility anisotropy () tensors accurately back-calculate the experimental PCSs measured in the immediate vicinity of the site of interest. The present work investigates the situation where only the local structure of a protein region or bound ligand is to be determined rather than the structure of the entire molecular system. In this case, the need for gathering structural information from tags deployed at multiple sites may be queried. Our study presents a computational simulation of the structural information available from samples produced with single tags attached at up to six different sites, up to six different tags attached to a single site, and in-between scenarios. The results indicate that the number of tags is more important than the number of tagging sites. This has important practical implications, as it is much easier to identify a single site that is suitable for tagging than multiple ones. In an initial experimental demonstration with the ubiquitin mutant S57C, PCSs generated with four different tags at a single site are shown to accurately pinpoint the location of amide protons in different segments of the protein.

Post-Cretaceous structural reconstruction of the west Central Iranian micro-plate: Insights from structural and magnetic fabrics (AMS) constraints

The Central Iranian Micro-plate (CIM) is a dismembered piece of northern Gondwana. The aim of this study is to reconstruct the post-Early Cretaceous structural evolution of the western edge of CIM in the light of the integration of regional to the micro-scale structural data with minor Anisotropy of Magnetic Susceptibility (AMS) analyses. Our original field measurements on the structural architecture of the study area show main NW-SE and E-W structural trends that are accompanied by structural evidence for superposition. However, paleostresses obtained from fault and fold analysis (stress inversion method on faults and statistically π-plane and β-axis solution on folds), statistical Fry center-to-center analysis on the oriented thin-sections integrated with AMS results suggest that the study area has experienced a NE-SW-directed compressional regime since Paleocene time followed by a post-Early Miocene, roughly N–S-directed, regional compressional regime. Furthermore, the results of this work confirm the consistency between regional-micro structural analysis and AMS analysis. The most of samples show composite (sedimentary + tectonic) magnetic fabric and intermediate arrangement in the orientation of the magnetic fabric. Reconciling our results with published structural and AMS data suggests the changes in the regional stress regime in the western CIM has been occurred in response to the long-term stress transition from the infant Late Cretaceous–Paleogene subduction of the Neo-Tethys Ocean to the mature Cenozoic stages of the Zagros collision and the consequent Neogene tectonic reorganization in the hinterland domains of the southern Eurasian plate.

Mush ado about the Ratagain Complex, NW Scotland: insights into Caledonian granitic magmatism and emplacement from magnetic fabric analyses

The anisotropy of magnetic susceptibility (AMS) is used to reveal subtle mineral alignment fabrics in apparently isotropic crystalline lithologies, including granites. Such petrofabrics can be produced by emplacement-related magma flow or post-emplacement tectonic strain. However, discriminating between flow-related and tectonic fabrics using field observations alone may be challenging and is usually a broad and arbitrary interpretation. In this contribution, we employ a range of magnetic analyses to characterize the origin of the petrofabric in the c. 425 Ma Ratagain Complex, NW Scotland, a composite Late Caledonian granitic intrusion. Our detailed magnetic analyses reveal that whilst all intrusive units carry an ambient tectonic overprint, critically, this has not developed into an obvious tectonic fabric and contains a horizontal shortening component indicative of transpression. This appears at odds with the well-defined Silurian (Scandian phase) regional transtensional tectonic regime from c. 420–415 Ma onwards. Accordingly, we suggest that either the complex is younger than previously thought or that it existed as a crystal-mush close to the magmatic solidus for a protracted period after its initial emplacement. This study lays the foundations for much-needed further investigations into the detailed emplacement mechanisms, timescales and petrogenesis of individual granitic intrusions, to aid understanding of Late Caledonian tectonics. Supplementary material : Supplementary data to this article are available at https://doi.org/10.6084/m9.figshare.c.5941375 Thematic collection: This article is part of the Early Career Research collection available at: https://www.lyellcollection.org/cc/SJG-early-career-research

Magnetic fabric and sedimentary characterization of near-slope to basinal deposits from the Chicontepec Formation, central and southern region of the Tampico-Misantla basin

We report results of a study of the Chicontepec Formation magnetic fabric in the central and southern region of the Tampico-Misantla basin in the state border region between Veracruz and Hidalgo. Samples were collected at 16 sites corresponding to two main facies associations: channel-fill facies and channel overbank facies. The channel facies dominate the relief developing prominent geoforms adjacent to low hills developed in facies dominated by shales. Measurements were made on channel and overbank facies. Laboratory analyses include anisotropy of magnetic susceptibility (AMS) and remanence anisotropy (AARM), as well as isothermal remanence acquisition (IRM) and thermomagnetic curves to characterize magnetic mineralogy. The magnetic susceptibility values of the entire collection are of the order of 40 to 70 x10-6 SI, so the susceptibility fabric is controlled by the paramagnetic fraction. The IRM acquisition curves are near saturation with inductions &lt; 0.3 T and can be modeled with a low coercivity component contributing ~ 90% and a high coercivity component contributing &lt; 10%. The thermomagnetic curves are dominated by paramagnetic phases. In the AMS fabric, three types of behavior are observed, corresponding to a lesser extent to sedimentary fabrics (k3 ~ vertical), and mostly to incipient and well-developed tectonic fabrics. The sedimentary fabrics are characterized by the imbrication of the magnetic foliation perpendicular to the paleocurrent data obtained in the field, which are generally consistent from NW to SE. At sites with tectonic fabric, which generally correspond to sites closer to the deformation front, the magnetic lineaments are well clustered in the NW quadrant with low plunges. AMS and AARM fabrics may combine in complex patterns. AARM appears to record either maximum axis directions that correspond to alignment of elongated particles perpendicular to flow or the direction of thrust motion.

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.