Anisotropy Of Remanence Research Articles

Exploration of the Magnetic Properties of ZrCo:Co Bilayer Films: Effects of the Thickness of the Co Layer on the Anisotropy and Magnetic Interaction Parameters

The analysis of ZrCo:Co films with varying Co layer thicknesses reveals distinctive magnetic properties and behaviors. Despite significant roughness, the films exhibit uniform surfaces and complete crystallization at the nanoscale. Magnetic studies show positive remanence anisotropy, decreased coercivity Hc and remanent magnetization Mr with increasing film thickness, along with a linear correlation between thickness and surface roughness. Exchange interactions between grains and layers influence magnetic properties. Ferromagnetic resonance analysis demonstrates a direct correlation between film thickness and magnetization orientation preference, notably at δCo = 200 nm. These findings underscore the critical role of film thickness in determining microstructural and magnetic properties, offering insights for magnetic device and nanotechnology applications. Understanding these relationships may lead to thickness‐tunable magnetic materials. This study uniquely explores ZrCo:Co films, delving into how their magnetic properties vary with Co layer thickness, revealing novel magnetic behaviors.

On the early postclassic collapse of Plazuelas (Northern Border of Mesoamerica): Archaeomagnetic evidence based on full geomagnetic vectors

We report a detailed rock-magnetic, archaeomagnetic and absolute intensity investigation on burned in situ remains of the Plazuelas archaeological site (Northern Border of Mesoamerica). Fifty-six specimens were subjected to step-wise alternating field demagnetizations to retrieve characteristic remanence directions. All samples yielded evidence of stable, single-component magnetization carried by magnetite or Ti-poor titanomagnetite. Sixty-four specimens were selected for paleointensity experiments following the Thellier double heating technique, including remanence anisotropy correction. The archaeomagnetic dating, based on full geomagnetic vectors, was performed using the global geomagnetic models and the regional Paleosecular Variation Curves available for Mesoamerica. The most probable age intervals obtained for the burned floor of Site 1 (Casas Tapadas North) are within the interval 972AD – 744 AD. In the case of the burned floor of Site 2 (Casas Tapadas West), the ages obtained fall within 971 AD - 752 AD. In the case of the burned floor of Site 3 (South Sector), the ages obtained fall within the interval 752 AD – 969 AD. The calculation of the most probable age intervals, carried out using the Bootstrap resampling method, provided the dates of 940 ± 6 AD, 896 ± 14 AD and 883 ± 14 AD, respectively. These ages agree well with various archaeological hypotheses on the sudden collapse of Plazuelas as a result of intentional destruction, mutilation and generalized firing due to the local war and/or social unrest.

Improved anisotropy of magnetic remanence results from vectorial readings using novel refinement method

SUMMARYAnisotropy of magnetic remanence (AMR) is typically obtained by imparting a remanence through a sequence of reference directions and subsequent measurement of the remanent magnetic moment with a separate device. This gives rise to potential misalignments which can affect the resultant anisotropy tensor. Vectorial measurements from rock magnetometers are favourable to obtain the best estimate of the anisotropy tensor but make the results highly dependent on the exact knowledge of the reference directions. This can be partly overcome by using the projection of the remanence vector on the reference direction instead of using the full vector in the calculation of the best-fitting anisotropy tensor. Since AMR experiments are laborious, it is troublesome to compensate the loss in information with additional measurements. This paper demonstrates an iterative refinement method to recover the original reference directions and therefore to improve the results of AMR experiments by using full vectorial readings. The method works well with a six-axis protocol for misalignment of the reference directions up to 25° and for degrees of anisotropy up to 250 per cent, which covers most experimental and geological cases.

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 < 0.3 T and can be modeled with a low coercivity component contributing ~ 90% and a high coercivity component contributing < 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.

Rock Magnetic Signature of Heterogeneities Across an Intraplate Basal Contact: An Example From the Northern Apennines

AbstractHeterogeneities in the magnetic signature along intraplate shear zones complicate their correlation with the physical processes that are involved in the geodynamic evolution of megathrusts. Isolating the preferred orientation of different magnetic minerals may provide insights into faulting processes, tectonics, and strain partitioning. Studies of exhumed analogs are fundamental to constrain variations in the magnetic properties with respect to a geodynamic context of intraplate shear zones. This study uses a combined statistical and magnetic approach to separate the contribution of coexisting petrofabrics to better interpret the heterogeneities in the magnetic signature. The main results indicate that there is a strong dependency among the variation in the magnetic properties and their anisotropy with the distance from the thrust faults and strain localization within the shear zone. Close to the main thrust, we observed a shear‐related fabric, indicating a high degree of non‐coaxial strain. Away from the thrust faults, the degree of anisotropy and the ellipsoids' oblateness gradually diminishes and subfabrics related to previous tectonic events or less intense deformation become dominant. Our observations also indicate strain decoupling across the basal thrust with dominant vertical uniaxial strain within the footwall. In contrast characterization of the anisotropy of magnetic remanence provides significant information on the variable response of different subpopulations of ferromagnetic minerals to shearing, indicating different degree of reworking or independent deformation processes.

Archaeomagnetic evidence of a likely earlier occupation of “El Caracol” lava flow (Zacapu Malpaís, Western Mesoamerica)

A comprehensive archaeomagnetic investigation was carried out on seven ceramic fragments recovered at the "El Caracol" lava flow in the Zacapu Malpaís –Michoacan state, Mexico –. A full set of magnetic-mineralogy experiments (encompassing thermomagnetic curves, hysteresis loops, backfield curves, and isothermal remanent magnetization acquisition measurements) were carried out. The experimental methodology also considers magneto-chemical alteration detection, cooling rate, and remanence anisotropy effects to ensure reliable archaeointensity determinations. Five of the seven ceramic fragments – a pipe (potsherd I), vessel's supports (potsherd II and V), a vessel's wall-fragment (potsherd III), and a pipe's nozzle (potsherd VII) – yielded archaeointensity results within the established acceptance criteria to guarantee quality data. Thermal demagnetization of potsherds I, II, V, and VII shows between two and three magnetization components: one associated with potsherd's fabrication, the second with sample's reheating, and the third one, when present, with a viscous component. For each of the first two components, an intensity value was calculated. Potsherds I, II, III, and VII yielded archaeointensity values between 30 and 40 µT, while potsherd V had a much lower value <20 µT. Although secular variation models do not predict such low intensities, similar values have been reported for the center and south of Mexico. Archaeomagnetic dating was carried out with two regional Paleosecular Variation Curves. The "El Caracol" lava flow is an area with human occupation reported from AD 1200. The results obtained in this work, on the contrary, envision the possibility of an early occupation of the site.

Decrypting Magnetic Fabrics (AMS, AARM, AIRM) Through the Analysis of Mineral Shape Fabrics and Distribution Anisotropy

AbstractAnisotropy of magnetic susceptibility (AMS) and anisotropy of magnetic remanence (AARM and AIRM) are efficient and versatile techniques to indirectly determine rock fabrics. Yet, deciphering the source of a magnetic fabric remains a crucial and challenging step, notably in the presence of ferrimagnetic phases. Here we use X‐ray micro‐computed tomography to directly compare mineral shape‐preferred orientation and spatial distribution fabrics to AMS, AARM and AIRM fabrics from five hypabyssal trachyandesite samples. Magnetite grains in the trachyandesite are euhedral with a mean aspect ratio of 1.44 (0.24 s.d., long/short axis), and &gt;50% of the magnetite grains occur in clusters, and they are therefore prone to interact magnetically. Amphibole grains are prolate with magnetite in breakdown rims. We identified three components of the petrofabric that influence the AMS of the analyzed samples: The magnetite and the amphibole shape fabrics and the magnetite distribution anisotropy. Depending on their relative strength, orientation and shape, these three components interfere either constructively or destructively to produce the AMS fabric. If the three components are coaxial, the result is a relatively strongly anisotropic AMS fabric (P' = 1.079). If shape fabrics and/or magnetite distribution anisotropy are non‐coaxial, the resulting AMS is weakly anisotropic (P' = 1.012). This study thus reports quantitative petrofabric data that show the effect of magnetite distribution anisotropy on magnetic fabrics in igneous rocks, which has so far only been predicted by experimental and theoretical models. Our results have first‐order implications for the interpretation of petrofabrics using magnetic methods.

Magnetic fabric of the Parashi stock and related dyke swarm, Alta Guajira (Colombia): The Caribbean-South American plates oblique convergence

Anisotropy of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) were used to evaluate the emplacement history of the Parashi stock and related dyke swarm situated in NW Colombia. The average magnetic susceptibility of 4.5×10-2 SI, in conjunction with low-coercivity components provided by the isothermal remanence and thermomagnetic curves with net Verwey and Curie transitions, indicates that multidomain magnetite records the anisotropy directions. The similar orientation and shape of the AMS and AAR ellipsoids indicate the absence of very fine magnetite with an inverse fabric. The magnetic foliation is the best-defined fabric element in these rocks and outlines a concentric structure, elongated parallel to the NE-SW direction of the pluton. Crystallisation age of the stock and dykes (51-47 Ma), along with pressure of emplacement determination indicate that the stock and the dyke swarm probably formed simultaneously, and they were emplaced in the shallow crust (

Composite magmatic/magnetic fabrics evidences late AMS in syn-tectonic dikes in the Monteiro-Sumé plutonic-volcanic complex (NE Brazil)

Interpretations of flow fabrics in dikes using anisotropy of magnetic susceptibility (AMS) are based on the orientation of the magnetic fabric recorded next to the dike walls. However, uncertainties remain when AMS is sensitive to parameters such as grain size and composition of the magnetic carriers and deformation of the magma. We study subvolcanic andesite to dacite dikes associated with granite plutons that intrude the basement rocks. The dikes have magnetic susceptibilities mostly between 10−3 and 10−2 SI carried by Fe–Ti oxides. AMS shows fabrics that would be consistent with a lateral movement of the magma. However, the anisotropy of anhysteretic remanence (AAR) and silicate shape preferred orientation (SPO) indicate that the melt moved upward based on the steeply plunging lineations detected by AAR and SPO. Furthermore, the obliquity of the AAR foliations in the dike margins indicates a component of transtension resolved in the dike walls. As there is no evidence for internal deformation of titanomagnetite, AMS would record its late growth in the tectonic extension direction. The magnetic subfabric concealed by late AMS therefore documents an earlier tectonic episode and evidence the limits of using just AMS directions to constrain the emplacement of syntectonic magmas.

Anisotropy of out-of-phase magnetic susceptibility as a potential tool for distinguishing geologically and physically controlled inverse magnetic fabrics in volcanic dykes

Among the mechanisms of the mass transport within the Earth's crust and the upper mantle the magma movement within the dykes is very important. In some dykes, the magma movement is represented by almost free flow infilling more or less open fractures in the host rocks, while it has character of forceful injection of the host rocks in the other dykes. The magnetic fabric originated by the free flow is characterized by the magnetic foliation and magnetic lineation approximately parallel to the dyke plane (normal fabric) whereas the forceful injection gives rise to the magnetic foliation perpendicular to the dyke plane defining the intermediate or inverse magnetic fabric. It is known, however, that the inverse magnetic fabric can also originate through the free flow of magma in the case when the minerals carrying the AMS are represented by single-domain (SD) grains. In order to distinguish between the two mechanisms controlling the intermediate/inverse fabric, the anisotropy of magnetic remanence (AMR) is often used, because it indicates the shape preferred orientation of ferromagnetic minerals regardless of their domain state. We show that not only AMR, but also the anisotropy of out-of-phase magnetic susceptibility (opAMS) is conformable with particle shape regardless of the magnetic state of the particle. Consequently, the opAMS, which is measured automatically with the standard AMS using the KLY-5 Kappabridge, may substitute the AMR at least in some cases of volcanic dykes.

Archeointensity of the Four Corners Region of the American Southwest

AbstractNew paleointensity experiments were conducted using the IZZI protocol (a variation on the Thellier‐Thellier method) on 289 specimens from 54 baked pottery fragments collected from four archeological sites in the American Southwest. Anisotropy experiments were conducted to correct for anisotropy of remanence, a common problem in archeological material. Additionally, the effect of cooling rate was evaluated and the calculated paleointensity values were adjusted accordingly. Using the Thellier graphical user interface program, the specimen results were analyzed, averaged by sample (i.e., pottery fragment), filtered for the highest quality, and converted to Virtual Axial Dipole Moments (VADMs). Stylistic evidence, historical documentation, and dendrochronology analyses provide age constraints with up to decade resolution for the VADM results. We compared these new results with the highest quality previously published paleointensity values from the Four Corners region of the American Southwest—defined here as the four states of New Mexico, Arizona, Utah, and Colorado. None of the previously published data were corrected for cooling rate and only some were corrected for anisotropy, resulting in a systematic bias between data sets. To accommodate this difference, an estimated cooling rate correction was applied to all the previously published data. No correction can be made for anisotropy as this is specimen specific. Our estimated cooling rate correction and the empirical correction applied to the new data both require an estimation of the historical cooling rate of the pottery. Experimental pottery firings using one ancient technique and outfitted with thermocouples were conducted to determine the historical cooling rate.

Anisotropy of Full and Partial Anhysteretic Remanence Across Different Rock Types: 1—Are Partial Anhysteretic Remanence Anisotropy Tensors Additive?

AbstractSeveral types or grain sizes of ferromagnetic minerals can contribute to a rock's remanence and anisotropy of remanence. Each subpopulation may have a different fabric. Measuring anisotropy of partial anhysteretic remanent magnetization (ApARM) allows one to determine the anisotropy contribution of subpopulations with different coercivity distributions. Separating these contributions to remanence anisotropy can provide information about early versus late stages of deformation in fabric studies and is the basis for improved anisotropy corrections in paleomagnetic studies. Unfortunately, collecting multiple ApARM tensors on each specimen is time‐consuming and not often done. Measuring a smaller number of carefully chosen ApARM tensors and obtaining the remaining tensors of interest by tensor calculation would be more efficient. This can only be done, however, when ApARM tensors are additive. Here we investigate the additivity of ApARM tensors in a range of lithologies, by measuring a total of seven ApARM and anisotropy of anhysteretic remanent magnetization (AARM) tensors for each specimen, and comparing the tensors calculated from a combination of ApARM tensors to the corresponding measured AARM. Differences in principal directions between measured and calculated tensors are often smaller than the confidence angles of the measurements. Mean anhysteretic remanences are additive to within ±5%. The anisotropy degree varies by ±30% (k′) or ±0.15 (P), and the shape parameter U by ±0.4. These error limits will help to determine whether or not it is necessary to measure each ApARM tensor in future fabric or paleomagnetic studies, or if these tensors can be calculated from a smaller set of measurements.

Anisotropy of Full and Partial Anhysteretic Remanence Across Different Rock Types: 2—Coercivity Dependence of Remanence Anisotropy

AbstractMagnetic fabrics are powerful tools in structural geology and tectonic studies, because they provide a fast and efficient measurement of mineral alignment, which helps interpret a rock's (de)formation history. The magnetic fabric of remanence‐carrying minerals provides useful information when these grains record different deformation stages than the bulk minerals in a rock. When rocks contain several subpopulations of remanence‐carrying minerals, each of these potentially displays a distinct fabric. This can lead to complex remanence anisotropies, being a superposition of all subpopulations' individual anisotropies. Characterization of partial remanence anisotropies has been used to investigate changes in fabric with grain size. However, most studies still report one bulk remanence anisotropy tensor per sample, and it remains to be determined how commonly different populations of remanence‐carrying grains reflect different subfabrics. Based on a large sample collection including 93 specimens from different lithologies, we have investigated the coercivity dependence of anisotropy of (partial) anhysteretic remanent magnetization A(p)ARM. We find that the principal directions, degree, and shape of A(p)ARM are generally dependent on the coercivity window used to impart the anhysteretic remanent magnetizations (ARMs). Depending on the carrier minerals and their fabrics, ARM anisotropy can either increase or decrease when the ARMs are applied over larger coercivity windows. Additionally, the coercivity fraction that dominates the ARM anisotropy is not always the coercivity fraction that acquires the strongest mean ARM. This illustrates the complexity of characterizing remanence anisotropy, and highlights the importance of carefully choosing experimental parameters in A(p)ARM determination for both magnetic fabric and anisotropy correction studies.

Magnetic fabrics of the neoproterozoic piquiri syenite massif (Southernmost Brazil): Implications for 3D geometry and emplacement

The study of magnetic fabrics and rock magnetic properties, together with geological and structural mapping, was carried out in a syenite pluton to investigate its shape and emplacement history. The Piquiri Syenite Massif (PSM) is an alkaline pluton which exhibits S >> L magmatic fabric and is interpreted to be part of the last Neoproterozoic post-collisional magmatic episodes in southernmost Brazil. Thermomagnetic curves, hysteresis data and coercivity spectra obtained from representative samples of different facies in the massif reveal that magnetic susceptibility is dominated by ferromagnetic minerals, especially magnetite. Magnetic fabric data were determined by using Anisotropy of Magnetic Susceptibility (AMS) and Anisotropy of Anhysteretic Remanence (AARM). Both fabrics are coaxial, and the parallelism of AMS and AARM tensors in more than 84 % of the sampled sites rules out the possibility of significant effects of Single Domain (SD) crystals. The magnetic foliation is concordant with the magmatic foliation field measurements, both parallel to pluton contacts, with high, inward dip angles. The magnetic lineation shows distinct but related behaviour from one facies to another. It is dominantly subvertical in the marginal facies rocks and plunges at moderate to shallow angles in the main facies. It is sub-horizontal in the quartz-syenites and plunges at shallow angles in the granitic rocks. Oxidizing conditions determined from the study of magnetic mineralogy leads to challenge former interpretation of in situ differentiation and crystallization and points to the multi-intrusive character of the pluton. Field relations such as fragments of marginal facies rocks found within the main facies rocks, which are in turn intruded by quartz-syenites, together with the general absence of contact metamorphism except near the marginal facies, lead to interpret that a sequence of magmatic pulses have built up the pluton. Thus, a first magmatic pulse may have heated the host rocks and resulted in the marginal facies which was followed by the next pulses to form the main facies and the quartz-rich varieties, therefore constructing the pluton from outside inwards.

Relative paleointensity estimates from magnetic anisotropy: Proof of concept

Relative paleointensity data from sedimentary rocks play an important role to decipher the workings of the geodynamo and to correct for atmospheric cosmogenic radionucleide production, so it is important to understand how sediments acquire remanent magnetizations and to better assess the quality of relative paleointensity data. We present experimental results from sediments deposited in controlled magnetic fields to observe the changes in magnetic anisotropy as a function of applied field strength going from near Earth-like values to almost full saturation. Relative paleointensity values followed a very well defined power law through the entire range of applied field intensities. Magnetic remanence fabrics evolved from oblate with maximum anisotropy axes in the sedimentary plane at low field strengths to prolate with maximum anisotropy axes parallel to the applied field direction at high fields. Anisotropy of magnetic susceptibility also evolved with field strength, but in a much less coherent manner than anisotropy of magnetic remanence. The experiments used well-characterized, natural sediments containing single domain magnetite, which made it possible to numerically model the data. The model matches the field dependency of both relative paleointensity and magnetic fabric development using a simple assumption that a large proportion (∼80%) of the remanence carriers in the sediments are unable to align with the magnetic field while a small fraction are free to align. Anisotropy of magnetic remanence thus holds promise to improve and assess relative paleointensity estimates and helps improve theoretical treatment of magnetic recording in sediments.

Anisotropy of (partial) isothermal remanent magnetization: DC-field-dependence and additivity

SUMMARY Anisotropy of isothermal remanent magnetization (AIRM) is useful for describing the fabrics of high-coercivity grains, or alternatively, the fabrics of all remanence-carrying grains in rocks with weak remanence. Comparisons between AIRM and other measures of magnetic fabric allow for description of mineral-specific or grain-size-dependent fabrics, and their relation to one another. Additionally, when the natural remanence of a rock is carried by high-coercivity minerals, it is essential to isolate the anisotropy of this grain fraction to correct paleodirectional and paleointensity data. AIRMs have been measured using a wide range of applied fields, from a few mT to several T. It has been shown that the degree and shape of AIRM can vary with the strength of the applied field, for example, due to the contribution of separate grain subpopulations or due to field-dependent properties. To improve our understanding of these processes, we systematically investigate the variation of AIRM and the anisotropy of partial isothermal remanence (ApIRM) with applied field for a variety of rocks with different magnetic mineralogies. We also test the additivity of A(p)IRMs and provide a definition of their error limits. While A(p)IRM principal directions can be similar for a range of applied field strengths on the same specimen, the degree and shape of anisotropy often show systematic changes with the field over which the (p)IRM was applied. Also, the data uncertainty varies with field window; typically, larger windows lead to better-defined principal directions. Therefore, the choice of an appropriate field window is crucial for successful anisotropy corrections in paleomagnetic studies. Due to relatively large deviations between AIRMs calculated by tensor addition and directly measured AIRMs, we recommend that the desired A(p)IRM be measured directly for anisotropy corrections.

Forward and inverse modeling of magnetic data under complex magnetism effects: Remanence, self‐demagnetization and magnetic anisotropy

Forward and inverse modeling of magnetic data under complex magnetism effects: Remanence, self‐demagnetization and magnetic anisotropy

Grain-size-dependent remanence anisotropy and its implications for paleodirections and paleointensities – Proposing a new approach to anisotropy corrections

Paleomagnetic data provide information on the evolution of the Earth's magnetic field, and are used to reconstruct plate motions. One fundamental assumption underlying these interpretations is that the magnetization of a rock reliably records the direction and intensity of the magnetizing field, i.e. that the magnetization is parallel to the field direction, and the intensity of magnetization is proportional to the field strength. Preferred alignment or anisotropic distribution of magnetic grains can affect both the direction and the intensity of magnetization. Therefore, correction techniques, employing the anisotropy of magnetic susceptibility (AMS), thermal remanence (ATRM), or anhysteretic remanence (AARM) are used to account for these effects. We find that AARM within the same rock can vary dramatically with coercivity/grain size, so that anisotropy corrections can also depend on how AARM was measured.A consequence of the dependence of AARM on coercivity is that although a specimen may have been magnetized in a single direction, different grain size fractions may record magnetizations in different orientations. These directional variations, as revealed during progressive alternating field (AF) demagnetization, could erroneously be interpreted as changes in field or reorientation of the rock unit, when in reality they are related to grain-size-dependent remanence anisotropy. Similarly, intensity variations caused by grain-size-dependent anisotropy may bias paleointensity estimates. These observations have important consequences for studies on the evolution of the Earth's magnetic field, magnetic overprinting, and paleogeographic reconstructions.

Anisotropy of Stable Single Domain Ferrimagnetic Particles in a Rock Sample from Gyroremanent Magnetization and Comparison with Other Anisotropy Methods

The orientation of stable single domain (SSD) ferrimagnetic particles in an igneous rock sample was determined by a sensitive technique utilizing gyroremanent magnetization (GRM). Components of GRM were measured in the sample upon exposure to an alternating field (AF) at various orientations in 3 orthogonal planes. The major components of GRM exhibited a sin(2θ) dependence on AF orientation in the respective perpendicular planes. This was in accordance with theory [1] and contrary to some previously reported experimental results on magnetic recording tape, which produced a distorted sin(2θ) dependence of the GRM [1]. The explanation is likely due to the SSD ferrimagnetic particles in the rock sample being more dispersed (less interacting) compared to the highly interacting SSD particles in the magnetic tape sample of the previous study. The GRM results were consistent with another remanence anisotropy method, anisotropy of isothermal remanent magnetization (AIRM). This method again measures the anisotropy of the remanence carrying ferrimagnetic particles, but the IRM is also acquired by larger multidomain (MD) particles as well as by the SSD particles. The results were also consistent with the visible rock anisotropy (petrofabric), the anisotropy of magnetic susceptibility (AMS), and the shear wave velocity anisotropy. A comparison of all the methods demonstrated that the fine SSD particles, which make up only a small proportion of the rock, were aligned in quite a similar orientation to that of the main rock forming minerals that constituted the bulk of the sample.

Diverse response of paramagnetic and ferromagnetic minerals to deformation from Intra-Carpathian Palaeogene sedimentary rocks: Comparison of magnetic susceptibility and magnetic remanence anisotropies

All the minerals in a rock contribute to its anisotropy of magnetic susceptibility (AMS). In weakly magnetic sedimentary rocks, the strongest contributors are the paramagnetic minerals, predominantly represented by clay minerals, together with the ferrimagnetic minerals that are typically magnetite and/or maghemite. In contrast, ferrimagnetic minerals solely control the anisotropy of magnetic remanence (AMR). An investigation of both AMS and AMR can therefore help distinguish among the deposition, diagenetic and deformation histories of the paramagnetic and ferrimagnetic minerals in the same rock specimen. We present a test case from relatively weakly deformed Intra-Carpathian Palaeogene sandstones (Skorušina Hills, Slovak Republic) where AMR and AMS fabrics generally coaxial yet also exhibited notable differences. In particular, AMR foliations were more readily deflected away from the bedding plane, perpendicular to the maximum stress axis, than the AMS foliations. These factors are interpreted in terms of higher sensitivity of the ferrimagnetic minerals to ductile deformation than that of the paramagnetic clay minerals.