Ann Hirt

In the last few years Anisotropy of Magnetic Susceptibility (AMS) in undeformed clay sediments has been increasingly used to unravel the tectonic history of sedimentary basins formed both in compressional and extensional tectonic settings. In extensional sedimentary basins it was demonstrated that the magnetic lineation is tectonically controlled and is oriented perpendicular to the normal faults. The origin of the

During the past few years, the anisotropy of magnetic susceptibility (AMS) has been increasingly considered as a successful method to study subtle deformation in sediments where conventional strain markers are not available, such as clay sediments. In the Mediterranean region, AMS studies on Neogene to Quaternary clay sediments located in different tectonic settings show a systematic correspondence between the observed

The investigation of rocks and minerals in low magnetic fields may be a good and relatively inexpensive alternative of the more or less standard high-field rock magnetic techniques. The Multi-Function Kappabridge Set measures the "in phase" susceptibility, the relative changes of the "out of phase" susceptibility and the magnetic loss angle in variable magnetic fields, at variable operating frequencies, and

The magnetic properties of a sediment core from a high altitude lake in the Swiss Alps were compared with palynological and geochemical data to link climatic and mineral magnetic variations. According to pollen data, the sediments extend from the present to the Younger Dryas, i.e., they cover more than 10,000 years of environmental change in the Alps. The major change

ABSTRACT Magnetotactic bacteria produce chains of magnetite nanoparticles, which are called magnetosomes and are used for navigational purposes. We use these cells as a biological template to prepare a hollow hybrid material based on silica and magnetite, and show that the synthetic route is nondestructive as the material conserves the cell morphology as well as the alignment of the magnetic particles. The hybrid material can be resuspended in aqueous solution, and can be shown to orient itself in an external magnetic field. We anticipate that chemical modification of the silica can be used to functionalize the material surface in order to obtain multifunctional materials with specialized applications, e.g. targeted drug delivery.

A series of large diameter calcite–muscovite aggregates has been prepared from calcite and muscovite powders, in order to gain a better understanding of how texture develops in impure carbonate rocks. The development of the microstructure and the crystallographic preferred orientation (CPO, texture) during the preparation process is described. The synthetic rocks have been fabricated from powders of calcite and muscovite

ABSTRACT Anisotropy of magnetic susceptibility (AMS) measured in the presence of low and high fields, at ambient and low emperatures(17K), has been used to separate ferromagnetic(s. l.), paramagnetic and diamagnetic sub-fabrics from a highly deformed, low-grade metamorphosed marble shear zone in southwest Switzerland. The AMS and bulk susceptibility obtained from these marbles reflect developmentof crystallographicpreferred orientations, as well as the ratio of diamagneticmatrix calcite to paramagnetic secondary phases. The magnetic fabrics in two of the three study locations is produced by iron-rich calcite, and display an inverse relationship to structural cleavage. Preferred orientations of calcite c-axes correspond to the directions of the separated diamagnetickmax•

ABSTRACT The anisotropy of magnetic susceptibility(AMS) has been used as an indicator of deformation, and in certain cases strain, in rocks for over fifty years. Advantages of using AMS to describe deformation is that low-field AMS is relatively fast to measure and it is very sensitive in detecting mineral alignment. However interpretation of AMS results is not always straightforwardand requires a good understanding of the mineral phase or phases, which contribute to the magnetic fabric. Numerous studies use the intensity of bulk susceptibilityto interpret whether diamagnetic, paramagnetic or ferromagneticminerals control the observed fabric. Such a criterion can be misleading since minerals responsible for the anisotropy are not always the minerals that make the largest contribution to the bulk susceptibility. Exampleswill be given from differentrock types to illustratethe role that mineralogy has on interpretingAMS results.

The structure of columnar-jointed lava flows and intrusions has fascinated people for centuries and numerous hypotheses on the mechanisms of formation of columnar jointing have been proposed. In cross-section, weakly developed semicircular internal structures are a near ubiquitous feature of basalt columns. Here we propose a melt-migration model, driven by crystallization and a coeval specific volume decrease inside cooling and solidifying columns, which can explain the observed macroscopic features in columnar-jointed basalts. We study basalts from Hrepphólar (Iceland), combining macroscopic observations, detailed petrography, thermodynamic and rheological modelling of crystallization sequences, and Anisotropy of Magnetic Susceptibility (AMS) of late crystallizing phases (that is, titanomagnetite). These are all consistent with our proposed model, which also suggests that melt-migration features are more likely to develop in certain evolved basaltic lava flows (with early saturatio...

Theoretically, within a given pelitic rock in which the main paramagnetic carriers are white mica and chlorite and in which, judging from the AMS parameters, AMS is controlled by the paramagnetic carriers, the results of X-ray pole figure goniometry should show a qualitative relationship with AMS. This idea is tested on single-phase deformed, low-grade pelites of the Lower Palaeozoic Brabant

ABSTRACT Dikes crosscutting existing folds or foliation are one of the classic time markers used in establishing relative geological chronology. We examine the paleomagnetic directions and magnetic fabric in a deformed gneiss from the Southern Steep Belt, which lies immediately north of the Insubric fault, and in an aplite dike that transects this foliation. No clear foliation or other evidence of internal deformation is discernible in the aplite dike in the field and it was originally interpreted as post-tectonic, with its intrusion age placing a young limit on the timing of deformation in the adjacent gneiss. The aplite dike does not carry a stable remanent magnetization and cannot be used to resolve the age of intrusion. The characteristic paleomagnetic remanence in the gneiss is compatible with Eurasian paleomagnetic directions during the last 20 Ma. These results suggest that the timing of magnetization postdates dextral motion along the Insubric and Rhine-Rhone faults. The low-field anisotropy of magnetic susceptibility (AMS) in the gneiss is controlled by the regional schistosity. High-field AMS suggests that both paramagnetic and ferromagnetic minerals contribute to the magnetic fabric, whereby the ferromagnetic minerals show a stronger lineation. This is further confirmed by the anisotropy of anhysteretic remanent magnetization (AARM). Rock magnetic experiments show that multi-domain magnetite is the main ferromagnetic mineral in the gneiss. Unexpectedly, the AMS results from the aplite dike show that it also has a magnetic fabric, which is shown by high-field AMS, AARM and rock magnetic experiments to be carried by superparamagnetic magnetite. The presence of magnetic fabric in the dike demonstrates that regional deformation was still on-going in the Southern Steep Belt of the Central Alps at the time of its intrusion.

In this study we analyse the magnetic and mineral fabric of clay sediments that appear homogeneous and not deformed at the outcrop scale. We integrate low-field, high-field and low-temperature AMS analyses with neutron diffraction pole figures analysis as an alternative approach to studying the deformation mechanisms that drive the development of the magnetic lineation in these sediments. The studied sediments

Low pressure plasma deposition (LPPD) of MoSi[sub 2] using 100% methane as a reactive powder carrier yielded a material with [approximately] 6 vol. % SiC, [approximately]6 vol.% SiO[sub 2] and [approximately]13 vol.% Mo[sub 5]Si[sub 3] and Mo[sub 5]Si[sub 3]C. The SiC phase formed during reactive spraying was cubic ([beta]-SiC) and exhibited a particulate morphology. The majority of the SiC particles were submicron in size and tended to be located at prior droplet boundaries. The SiO[sub 2] phase was along prior droplet boundaries. The Mo[sub 5]Si[sub 3] and Mo[sub 5]Si[sub 3]C phases were dispersed as particles within a MoSi[sub 2] lamella. In addition, a substantial amount of elemental carbon was observed in the as sprayed material. The volume fraction of SiC observed in the reactive plasma-sprayed MoSi[sub 2] is higher than that typically obtained using blended powders or co-injection. Annealing of the as-sprayed material increased the amount of SiC to [approximately]8 vol.% and ...

Deformation of carbonate rocks leads to crystallographic preferred orientations (CPOs) of calcite, which in turn generates an anisotropy of magnetic susceptibility (AMS). The use of the diamagnetic anisotropy, which arises from the preferential orientation of calcite, for texture characterization is usually hindered by (1) the weakness of the anisotropy, and (2) overlapping contributions from paramagnetic and ferromagnetic minerals to the AMS. In this study, the diamagnetic, paramagnetic and ferromagnetic sub-fabrics of synthetic calcite–muscovite samples have been separated using high-field torque measurements. The CPO of calcite and muscovite has been determined by neutron diffraction, and the magnetic sub-fabrics are compared to the AMS that was re-calculated from the CPO. The isolated diamagnetic sub-fabric shows a good correlation with the calcite texture for calcite concentrations above 70%. The paramagnetic sub-fabric is shown to be a reliable texture parameter for muscovite, even at a concentration of 5%. The results demonstrate the capability of the AMS method as a texture parameter in impure carbonate rocks.

In the brain, iron plays an important role, but also is potentially toxic if iron metabolism is disrupted. Excess iron accumulation in the brain has been shown to be associated with neurodegenerative diseases. However, identification of iron compounds in human tissue is difficult because concentrations are very low. Three types of magnetic methods were used to characterize iron compounds in

ABSTRACT Sediment and archeomagnetic data spanning the Holocene enable us to reconstruct the evolution of the geomagnetic field on time scales of centuries to millennia. In global field modeling the reliability of data is taken into account by weighting according to uncertainty estimates. Uncertainties in sediment magnetic records arise from (1) imperfections in the paleomagnetic recording processes, (2) coring and (sub) sampling methods, (3) adopted averaging procedures, and (4) uncertainties in the age-depth models. We take a step toward improved uncertainty estimates by performing a comprehensive statistical analysis of the available global database of Holocene magnetic records. Smoothing spline models that capture the robust aspects of individual records are derived. This involves a cross-validation approach, based on an absolute deviation measure of misfit, to determine the smoothing parameter for each spline model, together with the use of a minimum smoothing time derived from the sedimentation rate and assumed lock-in depth. Departures from the spline models provide information concerning the random variability in each record. Temporal resolution analysis reveals that 50% of the records have smoothing times between 80 and 250 years. We also perform comparisons among the sediment magnetic records and archeomagnetic data, as well as with predictions from the global historical and archeomagnetic field models. Combining these approaches, we arrive at individual uncertainty estimates for each sediment record. These range from 2.5° to 11.2° (median: 5.9°; interquartile range: 5.4° to 7.2°) for inclination, 4.1° to 46.9° (median: 13.4°; interquartile range: 11.4° to 18.9°) for relative declination, and 0.59 to 1.32 (median: 0.93; interquartile range: 0.86 to 1.01) for standardized relative paleointensity. These values suggest that uncertainties may have been underestimated in previous studies. No compelling evidence for systematic inclination shallowing is obtained from the analysis of the available database of Holocene sediment magnetic records. The analysis highlights the importance of collecting oriented cores, publishing and archiving unprocessed raw paleosecular variation determinations, and presenting a detailed chronology so that changes in the sedimentation rate can be assessed. With regard to future field models, workers should consider rejection of anomalous cores through comparisons to other sources and ensure that realistically large uncertainties are allocated to high-latitude declination records.

Two samples of six-line ferrihydrite (5Fe2O3.9H2O) were precipitated from an Fe(III) solution. The purity of the samples was verified by X-ray diffraction. Scanning electron microscope pictures indicate that the grains have good crystallinity and variable grain size (<0.5 to 100 mum). Mössbauer spectra show a broad asymmetric doublet without split components between 150 K and 250 K. Hyperfine magnetic splitting

The growth of the nanotechnology industry has led to an increased interest in characterizing magnetic nanoparticles. A natural material with well-defined grain size in the nanoparticle range is commercially available-horse spleen ferritin, an iron storage protein. Modeling of the magnetic properties of commercial horse spleen ferritin is often based on the assumption of a single-phase core of ferrihydrite (5Fe2O3.9H2O). Low

ABSTRACT Many minerals and rocks have low susceptibilities and magnetic anisotropies on the order of the noise level of the measuring instrument. Anisotropy is often not significant in these samples when using the standard measurement procedure. We propose a method that uses stacking of data to improve the signal-to-noise ratio, thus extending the dynamic range for measurement and allowing for assessment of the data quality. The method makes it possible to obtain consistent directions of the principal axes for samples with an anisotropy on the order of, or even slightly below, the noise level of the instrument. For noisy datasets, the stacking procedure makes it easier to recover correct directions. However, the degree P and shape U of the anisotropy ellipsoid show large variations. Large values of P, in combination with a badly defined U, may indicate noisy data rather than a large anisotropy. The stacking procedure is especially useful for determining the magnetic anisotropy of single crystals that often have a low susceptibility but must be measured with high accuracy.