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Analyzes isothermal remanent magnetization curves of rock-magnetic sample. Coercivity spectra; Use of expectation-maximization algorithm; Rock magnetism.

Abstract Anisotropy of magnetic susceptibility (AMS) has been used to infer finite strain fabrics in plastically deformed rocks, but there are few studies of magnetic properties in fractured fault rocks. Changes in magnetic and fractal properties of fractured granites from the Disaster Prevention Research Institute, Kyoto University (DPRI) 500 m drilling core towards the Nojima Fault and of the well-foliated fault gouge are described. Fractal analysis of fractured granites shows that the fractal dimension (D) increases linearly toward the gouge zone of the fault. In weakly fractured granites (D = 1.05–1.24), it was found that the degree of AMS correlates positively with the fractal dimension, suggesting a fracture-related magnetic fabric due to fracturing. In strongly fractured granites (D = 1.25–1.50), weaker, nearly isotropic AMS is found, suggesting erasure by the fragmentation of the magnetic minerals. Within the fault gouge zone, an isotropic AMS fabric was found, as well as twofold increases in magnetic intensity and susceptibility. These changes reflect the production of new magnetite grains, subsequently confirmed by hysteresis studies, which suggests that fault gouge might be regarded as the source of the regional geomagnetic field contrast along active faults. Thus, AMS is clearly a potentially useful tool for inferring the fracturing texture of magnetic minerals in fractured rocks and detecting active faults from the high susceptibility contrast of fault gouge. [ABSTRACT FROM AUTHOR]

Focuses on a paleomagnetic investigation of the Gory Bardzkie region in Poland. Rock magnetic study of Upper Devonian olistoliths from the Zdanow-Bardo-Mlynow allochthonous complex of the Gory Bardzkie region; Measurement of anisotropy of magnetic susceptibility.

The oxide mineralogy and rock magnetic properties of unmineralised banded iron-formations in selected portions of four drillholes in the Hamersley Basin, Western Australia are reviewed. In all four drillholes, petrographic studies indicate that primary euhedral to subhedral hematite is partially replaced by magnetite as a result of subsolidus reduction. All drillholes show partial recrystallisation of the secondary magnetite, suggesting that early subsolidus reduction was probably a regional event occurring during prograde metamorphism. Incomplete replacement of primary hematite by magnetite within and between sedimentary band structures indicates that equilibration in the magnetite stability field was not reached even at the mesoband scale. Subsequent subsolidus oxidation of magnetite and the formation of a second-generation hematite are documented in only two of the drillholes. Goethite-filled veins and thick selvages of goethite around some veins reflect movement of circulating oxidising fluids. The absence of goethite and second-generation hematite in two of the drillholes indicates that subsolidus oxidation is not a regional event, but very much localised. Rapid changes in down-hole susceptibility measurements correlate directly with detailed petrographic results as susceptibility readings change with the hematite/magnetite ratio on a mesoband scale. Acquisition of the main remanence correlates with the formation of hematite as the primary oxide phase followed by partial replacement by magnetite as a result of subsolidus reduction, supporting regional models requiring pre-folding remanence. The strong orientation of the primary hematite parent parallel to band structures in the banded iron-formations has influenced the direction of crystallisation remanent magnetisation during subsolidus reduction to the magnetite daughter. The strong planar alignment has also produced a planar magnetic fabric and marked anisotropy of magnetic susceptibility. A natural... [ABSTRACT FROM AUTHOR]

Measures the magnetic susceptibility (MS) of marine paleozoic rocks. Characterization of the two forms of magnetic signatures; Relationship of calcium carbonate concentrations and MS: Origin of MS in detrital rocks; Contribution of different paramagnetic minerals to MS in marine sediments.

Presents a study of a technique which may be used to nondestructively extract multiple length scales from carbonate rocks. Details regarding the technique, which uses nuclear magnetic resonance to exploit the spatially varying magnetic field inside the pore space itself; Why this technique is critical for efficient oil production; Other studies and techniques that may benefit from this process.

Abstract -- A magnetic anomaly near the centre of the Vredefort impact structure is attributed to remanent magnetism associated with a large meteorite impact at is similar to 2.0 Ga. The rocks that underlie the anomaly are shocked Archaean granites, which have extremely high remanent magnetism. We propose that the high remanence derives from elongated, micron-size single-domain magnetite particles found along shock-induced planar deformation features in quartz. The magnetite particles appear to have preferred magnetic dipole orientations, and are interpreted to have been intruded along the planar deformation features under extreme P-T conditions following the impact event. [ABSTRACT FROM AUTHOR]

Examines the low-temperature magnetic properties of magnetite from a rock magnetic perspective. Consideration of various Verwey transition theories; Analysis on the low-temperature anomaly in spontaneous magnetization; Assessment on multidomain remanence during low-temperature cycling.

Presents the detailed record of mineral magnetic properties of a loess-paleosol profile from Northeastern Bulgaria. Characterization of concentration-independent hysteresis parameters of rock; Impact of paleoclimatic conditions on the magnetic properties of rocks; Behavior of thermogenetic curves between phases.

Investigates a pseudo-Thellier relative paleointensity record and rock magnetic and geochemical parameters in relation to climate during the last 276 kyr in the Azores region. Comparison with conventional record; Facilitation of spectral analysis; Correlation of the clusters with the climate.

Presents the magnetic petrology of a suite of deep-crustal rocks from the Brien intrusion within the Proterozoic continental collision zone between the Grenville and Superior provinces of the Canadian Shield. Geology; Petrography; Geochemistry; Magnetic properties; Implications for magnetic anomalies of continental collision zones.

Reports on the results of a magnetic and geochemical study of Cretaceous rocks from the North Slope Basin of Alaska. Identification and distribution of postdepositional greigite and its contributions to the magnetization of the rocks; Magnetic properties of greigite-bearing sediments; Origin of the greigite-using geochemical and sulfur isotopic methods.

An introduction is presented in which the editor discusses various reports within the issue on topics including magnetic anisotropy of haematite natural crystals, magnetic subfabrics in polycrystalline rocks, and the Kapitan-Dimitrievo pluton case in Central Bulgaria.

The article discusses the highlights of an Earth Sciences Field seminar that was organized by the Earth Observatory of Singapore (EOS) in 2010. Topics discussed include the efforts done by volcanologists to study the Merapi volcano, its eruption in November, and the discovery of gems within the volcanic landscape. Also mentioned are the measurement of rock magnetism, how to monitor the speed of the river flow, and a field guide to be produced by teachers.

Abstract: Thermomagnetic curves are commonly used to characterize the magneto-mineralogy of basaltic rocks. It helps particularly for pre-selection of samples for paleointensity studies. However, the temperature dependence of the total magnetization is often different to the behavior of the remanence carriers. It is therefore of advantage to apply a new method to measure simultaneously the reversible and irreversible magnetization part. The method is based on a modified version of the Variable Field Translation Balance (VFTB). It is shown that the temperature dependence of the remanence carriers may be distinctly different to the total magnetization as seen in ordinary thermomagnetic curves. [Copyright &y& Elsevier]

The article discusses the history of the the University of Toronto, originally called Erindale College named after the local historical village and it is now called University of Toronto Mississauga (UTM). Topics include the eminent poeple who contributed to the development of the campus including astronomer John Percy, geophysicist Principal J. Tuzo Wilson, who established Earth and Planetary Sciences program and geophysicist David Dunlop who contributed the study of rock magnetism.

The article presents rock magnetic and geochemical analyses to distinguish the magnetic mineralogy and assess the possible environmental and geological implications at Qinghai Lake in North China. Rock magnetic, scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive analysis of X-ray (EDAX) analyses show that the primary magnetic carrier is greigite in the lacustrine sediments of Early Pliocene age.

We developed a theory of multidomain (MD) thermoviscous remanence that can be solved analytically to yield an expression relating the blocking temperature of a MD grain to its relaxation time. This expression is analogous to Néel's widely used theory of single‐domain (SD) thermoviscous remanence but yields a different time‐temperature relationship. The theory is based on a two‐domain model with a domain wall (DW) that can jump between different pinning sites. In contrast to previous theories of this kind, our theory considers repeated DW jumps rather than a single jump in isolation. It is shown that while SD remanence behavior is fully described by the two quantities (V,HK0), that is, volume and microscopic coercivity, MD particle remanence depends on three quantities: volume, Barkhausen volume, and DW pinning field, denoted (V,VBark,HK0). "Pullaiah" nomograms of this new theory show that while small MD grains behave almost identically to SD grains, larger grains show different slopes depending on the above quantities. The theory predicts that MD grains can be highly stable remanence carriers, in particular showing a high thermal stability. Grains with weak pinning fields, however, while thermally stable, are highly unstable under alternating field (AF) demagnetization, being demagnetized under fields of a few millitesla. Our theory also explains (1) why samples dominated by MD grains show curved vector demagnetization plots for both thermal and AF demagnetization, as well as (2) why MD grains affect thermal demagnetization plots even at high temperatures, while their remanence is completely removed within the first few AF demagnetization steps. Key Points: Repeated domain wall jumps in multidomain particles yield an analytical expression for relaxation times and blocking temperaturesMD grains have similar "Pullaiah" nomograms to SD grains, but with a different time‐temperature relationshipMD particles can be highly stable remanence carriers with respect to thermal demagnetization but can be very unstable under AF demagnetization [ABSTRACT FROM AUTHOR]

Skeletons of hermatypic corals (e.g., Porites) might have enormous potential as a high-resolution paleomagnetic recorder owing to their rapid and continuous growth over hundreds of years at a rate of up to 2 cm/year, although typical corals show an extremely weak intensity of remanence and low stability. We found that coral tsunami boulders with negligible amounts of calcite on Ishigaki Island show a measurable intensity of remanence; thus, we attempted to characterize the magnetic assemblages in this coral skeleton to determine whether it is of biogenic or detrital magnetite using first-order reversal curve (FORC) measurements, ferromagnetic resonance (FMR) spectroscopy, and petrological observations through field-emission type scanning electron microscope (FE-SEM) with an acid treatment. The FMR derivative spectra of coral skeleton samples represent multiple derivative maxima and extended low-field absorption, indicating the presence of intact biogenic magnetite chains. FORC diagrams represent a "central ridge" signature with a vertical spread. These FMR and FORC features indicate the magnetization of these coral skeletons that are mainly created using intact biogenic magnetites and mixtures of grains from collapsed biogenic magnetites, pseudo-single domain grains, and multi-domain grains such as detrital magnetite. FE-SEM observations confirm the presence of a chain-like structure of iron oxides corresponding to the features of biogenic magnetite. Therefore, the magnetic mineral assemblage in coralline boulders from Ishigaki Island consists of dominant biogenic-origin single-domain magnetite and a trace amount of detrital component, indicating that fossil coral skeletons in Ishigaki Island have potential for utilization in paleomagnetic studies. [ABSTRACT FROM AUTHOR]

The northeastern Turkey is located at the intensely deformed east Anatolian Collision Zone that is formed by the collision of the Arabian Plate with Eurasia. The region is one of the best examples of the continental collision zone in the world and exhibits an active north-south shortening and a young and widespread volcanism. In northeastern Anatolia, the ongoing motions of the Arabian and Eurasian Plates through a range of deformation processes have generated the Erzurum-Kars Plateau, a region of large-scale deformation and uplift observed at surface. However, the nature of deformation driven by the continental collision remains unresolved at depth. In this study, magnetotelluric (MT) data recorded at 74 sites constituting two intersecting profiles have been used to construct the characteristic electrical conductivity pattern associated with the intensely deformed east Anatolian Collision Zone beneath the Erzurum-Kars Plateau, northeastern Turkey, with the aim of imaging the 3D distribution of fluids in order to link it with subsurface rheological conditions. An equal number of colocated transient electromagnetic (TEM) sounding data were used to allow the static shift correction of the MT data; a borehole was also drilled inside the study area. We ran a one-dimensional inversion of TEM data in order to determine shift in MT data and a three-dimensional inversion using full components of MT impedance tensor previously corrected for static shift. The resulting models showed that two distinct conductive zones probably indicating local accumulation of melt exist at mid-to-lower crustal depths (15-45 km) throughout the Erzurum-Kars Plateau. The spatial distribution of these anomalously conductive zones mechanically characterizes weak areas that may permit flow of crustal materials in the collision zone. These conductive zones have been previously identified further west of the collision zone, which implies that the electrical characteristic of the collision zone is continuous from west to east beneath the Anatolian Plateau. The spatial extent of the conductive zones may suggest the presence of two localized crustal flow channels situated laterally parallel to the orogeny. These findings can potentially contribute to understanding of the crustal structure of collision zones, in particular east Anatolian Collision Zone, and the hypothesis that crustal flow can occur in orogenic belts. [ABSTRACT FROM AUTHOR]

The St. Patrick’s Day geomagnetic storm on March 17, 2015, has been chosen by the space community for synergetic analysis to build a more comprehensive picture of the storm’s origin and evolution. This storm had an unusually long (~ 17 h) main phase. During this period, many substorm-like activations occurred. These activations resulted in bursts of geomagnetically induced currents (GICs) in power lines on the Kola peninsula. To examine the substorm activations in more detail, we apply various data processing techniques for the world-wide array of magnetometers: the virtual magnetograms, magnetic latitude-local time (MLT) snapshots, and magnetic keograms. These techniques are simple tools that are supplementary to more advanced facilities developed for the analysis of SuperDARN, IMAGE, and CARISMA arrays. We compare the global spatial localization and time evolution of the geomagnetic X-component disturbance and magnetic field variability measured by the Hilbert transform of time derivative dB/dt. The latitude-MLT mapping of these magnitudes shows that very often a region with highest magnetic variability does not overlap with a substorm “epicenter” but is shifted to its poleward or equatorward boundaries. Highest variability of the geomagnetic field, and consequently intense GICs, are caused by medium-scale fast varying structures. There is no one-to-one correspondence between substorm intensity and GIC magnitude. [ABSTRACT FROM AUTHOR]

Previous studies have compiled relative paleointensity data for the last 2-3 Ma from individual paleomagnetic records obtained from marine sediment cores. These records have mostly been obtained by pass-through measurements, which are known to smooth and alter magnetic signals. Among many efforts, a standalone open-use graphical software UDECON has been developed to deconvolve pass-through measurement data. As an initial case study to assess the applicability of the software to deconvolve natural remanent magnetization (NRM) of a continuous paleomagnetic sample, we chose 40 discrete samples from a piston core recovered in the northeast Pacific. We measured NRMs after alternating field demagnetization at 20 mT for both discrete samples and a simulated continuous sample, made by connecting the discrete samples. The discrete samples show centimeter-scale variations in NRM. Such variations are smoothed out and mostly disappear in the results of the simulated continuous sample. However, after using the software to deconvolve the data, the variations are almost completely restored. Good agreement between the discrete sample data and the deconvolved data indicates that the deconvolution by the software is very successful. We observe detailed features of a directional reversal in the data from the discrete samples and in the deconvolved data but not in the data from the simulated continuous sample. This emphasizes that the deconvolution analysis by the software is a powerful tool to extract detailed features from continuous paleomagnetic records obtained by pass-through measurements. [ABSTRACT FROM AUTHOR]

Magnetic mineral inclusions in silicates are widespread in sediments as well as in igneous rocks. Because they are isolated from surrounding environment, they have potential to preserve original magnetic signature even in chemically altered sediments. Such inclusions may provide proxies to help differentiating the source of the host silicate. We measure magnetism of quartz and feldspars separated by chemical digestion of pelagic red clay. The samples are from the upper 15 m of sediments recovered at Integrated Ocean Drilling Program Site U1366 in the South Pacific Gyre. The quartz and feldspars account for 2.3-22.7 wt% of the samples. X-ray diffraction analyses detect both plagioclase feldspar and potassium feldspar. Plagioclase is albite-rich and abundant in the top ~ 7.4 m of the core. Potassium feldspar mainly occurs below ~ 10.4 m. The dominance of albite-rich plagioclase differs from a previous investigation of coarser fraction of sediments from the South Pacific. Saturation isothermal remanence (SIRM) intensities of the quartz and feldspars are 7.45 × 10−4 to 1.98 × 10−3 Am2/kg, accounting for less than 1.02% of the SIRM of the untreated bulk samples. The depth variations of the silicate mineralogy and the previously reported geochemical end-member contributions indicate that quartz and/or plagioclase above 8.26 m is likely to be Australian dust. In contrast, the relative abundance and the magnetic properties of quartz and feldspars vary below 10.42 m, without clear correlation with geochemical end-member contributions. We consider that these changes trace a subdivision of the volcanic component. Our results demonstrate that magnetism of inclusions can reveal additional information of mineral provenance, and chemical separation is an essential approach to reveal the environmental magnetic information carried by magnetic inclusions. [ABSTRACT FROM AUTHOR]

A combination of mineralogical, rock-magnetic and palaeomagnetic methods were employed in an attempt to shed a new light on the tectonism and paleogeography of Central Western Svalbard. The focus is on six metadolerite sites from the metamorphic Proterozoic–Lower Palaeozoic complex of south-western Oscar II Land (Western Spitsbergen). The primary mineral compositions of the metadolerites were strongly remineralized during Caledonian (sensu lato) greenschist-facies metamorphism although some younger tectonothermal modification is also apparent from the rock-magnetic studies. Rock-magnetic experiments supported by thin-section mineral identification and separation of Fe-containing fractions indicate that the main ferromagnetic carriers of the Natural Remanent Magnetization are represented by low-coercivity pyrrhotite and magnetite/maghemite. The investigated metadolerites are characterized by complex pattern of magnetization. The low-temperature palaeomagnetic components which demagnetized up to 250 °C, are characterized by high inclinations (~70–80°) potentially representing Mesozoic–Cenozoic remagnetization. The most stable middle-high temperature directions which demagnetized from 250 °C, were obtained from only two of six sites. Two Virtual Geomagnetic Poles calculated from two of the middle-high temperature site means do not correlate with the Laurussia reference path for syn- to post-Caledonian time. Two possible explanations of observed inconsistency are discussed. These are a modification of the Oscar II Land Caledonian basement geometry by listric faulting and/or tectonic rotations related to Daudmannsdalen–Protectorbreen high-strain (shear) zone. The results presented here suggest that post-Caledonian tectonic modification of the palaeomagnetic directions may be more a widespread feature of Western Svalbard. [ABSTRACT FROM AUTHOR]

Paleomagnetic and rock magnetic investigations were performed on a 64-cm-thick section of nonmarine unconsolidated muddy sediment from the Gosan Formation on Jeju Island, Korea. This sediment was recently dated to have been deposited between 22 and 17 kyr BP calibrated, with a sedimentation rate of 13-25 cm/kyr, based on many radiocarbon ages. Interestingly, stepwise alternating field (AF) demagnetization revealed characteristic natural remanent magnetizations with anomalous directions, manifested by marked deviations from the direction of today’s axial dipole field, for some separate depth levels. On the other hand, stepwise thermal (TH) demagnetization showed more complex behavior, resulting in the identification of multiple remanence components. For all TH-treated specimens, consistently two different components are predominant: a low-temperature component unblocked below 240-320 °C entirely having normal-polarity apparently within the secular variation range of the Brunhes Chron, and a high-temperature component with unblocking temperatures (Tubs) between 240-320 and 520-580 °C that have anomalous directions, concentrated in the ~ 13-34-cm-depth interval (~ 17-19 ka in inferred age) and possibly below ~ 53 cm depth (before ~ 20 ka). Rock magnetic results also infer the dominance of low-coercivity magnetic particles having ~ 300 and ~ 580 °C Curie temperature as remanence carriers, suggestive of (titano)maghemite and/or Ti-rich titanomagnetite and magnetite (or Ti-poor titanomagnetite), respectively. A noteworthy finding is that AF demagnetizations in this study often lead to incomplete separation of the two remanence components possibly due to their strongly overlapping AF spectra. The unusual directions do not appear to result from self-reversal remanences. Then, one interpretation is that the low-temperature components are attributable to post-depositional chemical remanences, associated possibly with the later formation of the mineral phase having Tub ~ 300 °C, whereas the high-temperature components are of primary detrital origin that survived later chemical influence. Accordingly, the unusual directions might record geomagnetic instability within the ~ 17-22 ka period manifested by multiple excursional swings, partly associated with the Tianchi/Hilina Pali excursion. However, further work is needed to verify this interpretation and distinguish it from alternative explanations that invoke rock magnetic complexities as the cause of the unusual directions. [ABSTRACT FROM AUTHOR]

The article discusses a study by G. Yancheva and colleagues regarding the paleoclimatic and paleoenvironmental details of the Huguangyan Maar Lake (HML), which is located at the Leizhou Peninsula in southern China. Topics include performing a rock magnetic and geochemical analyses to determine the reliability of the HML, the collection of the samples of the distribution patterns of rare earth element (REE), and the Chinese Loess Plateau (CLP)'s loess samples.

The author comments on a study that constructed a rock magnetic chronostratigraphy of the Shuram carbon isotope excursion at the Wonoka Formation in Australia. He questions the veracity of the magnetic signals measured by the researchers as the primary magnetic signals of the carbonates within the excursion may have been lost during early diagenesis. He suggests reconsidering the study's conclusion regarding the role of diagenesis in generating the Shuram Excursion.

The authors respond to a commentary on their study that constructed a rock magnetic chronostratigraphy of the Shuram carbon isotope excursion at the Wonoka Formation in Australia. They address a potential caveat affecting their conclusion regarding the magnetic signals measured in their study. They also explain factors behind their conclusion about the unlikely role of diagenesis in the origin of the excursion.

The article presents a study to examine airborne magnetic anomalies for the exploration of deep iron ore deposits in Daye, Hubei Sheng, China. Topics discussed include magnetic properties of rocks and ores in Daye iron mines, high resolution and accurate magnetic anomalies indicated by 1:10 000 airborne magnetic survey at line spacing of 50 to 100 meters and identification of location of unknown iron ore bodies by interactive inversion of the airborne magnetic anomalies.

The article discusses a study of Wajiertag magmatic V-Ti-Fe Magmatic Deposit located in China on the basis of magnetic anomalies. Topics discussed include characteristics of magnetic anomalies, physical properties of rock and ores and its comparison with Panzhihua deposits on the basis of metallogenic background and magnetic characteristics. It concludes formation of iron ore bodies during the later-stage magmatic cooling process.

The article discusses research investigating geophysical characteristics and criteria of prospecting in Wajiertag magmatic V-Ti-Fe deposit in Xinjiang, near Bachu Country, Chiuna. Topics discussed include analysis of magnetic properties of the rocks and ores, characteristic of airborne magnetic anomalies and gravity and the induced magnetization in iron and mafic and ultramafic complexes rocks leads to negative magnetic anomaly.

Argues that Mars, which has no magnetic field, once had a core dynamo that became active less than four billion years ago and has since become inactive. Discovery of remanent crustal magnetization by the Mars Global Surveyor; Implications of localized magnetic anomalies in the younger crust of Mars' northern hemisphere.

Abstract: A bulk ferromagnet is compared with typical nanomagnets and with a canonical spin-glass from the viewpoint of thermal hystereses. We cannot distinguish the bulk ferromagnet from the others by studying field-cooled and zero-field-cooled magnetization conventionally. On the other hand, effect of thermal cycles on the thermoremanent magnetization of the bulk ferromagnet is different from the others. Therefore, this effect can be a helpful distinction of ferromagnetic ordering. [Copyright &y& Elsevier]