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En el contexto de la Terapia Racional Emotivo-Conductual, se desarrollo la O’Kelly Women Beliefs Scale (OWBS) construida originalmente en Australia, para evaluar las creencias sobre el rol sexual que las mujeres pueden desarrollar como estereotipo. En una muestra de 974 mujeres australianas, el analisis factorial de los 92 reactivos originales mostro que 64 de ellos cargaron en un solo componente que explica el 18.2 % de la varianza total. El objetivo del presente estudio exploratorio es determinar la estructura factorial del OWBS, en 202 mujeres nacidas en E.E. U.U. La rotacion Varimax con punto de corte de autovalor en 3, arrojo que 37 items cargan en tres componentes que explican el 58.48 % de la varianza total. Los reactivos se agruparon en dos factores: Irracionalidad, con un total de 27 reactivos que se integraron en los componentes 1 y 3 (r = 0.8) y Racionalidad, con 10 reactivos integrados en el componente 2. El alfa de Cronbach fue de 0.91 para el Factor 1 y de 0.74 para el Factor 2. Los resultados indican que esta version del instrumento puede ser usada para evaluar tanto el contenido racional como el irracional de las creencias sobre el rol sexual de las mujeres nacidas en E.E. U.U.

In some basalt flows of the 1.1-billion-year-old Keweenawan Rift exposed at Mamainse Point,Ontario, there is a magnetic phase that holds a remanence antiparallel to the populations of magnetite and hematite that are typical of flows in the succession. The paleomagnetic and geological context of this component demonstrates that it is not a chemicaloverprint whoseremanence is attributableto a subsequently reversed geomagnetic field, but that the component is a self-reversal of the primary magnetization. Here we use rock magnetic experiments and Mossbauer spectroscopy to show that this phase occurs in the most oxidized flowsandisheldbya fine-grainedpopulationofhematitethatacquiredits self-reversedremanencethrough interactions with a phase of lower blocking temperature. We propose that this self-reversed hematite is a manifestation of the self-reversal phenomena that has been observed to occur experimentally during the transformation of maghemite to hematite and thathas been attributed to negative exchange coupling across the crystal lattices. We suggest that hematite formed in association with iron-silicates in the basalt flows carries a remanence reflective of the field in which it formed, but that martite (hematite pseudomorphed after magnetite) which formed through the progressive oxidation of magnetite to maghemite with subsequent inversion to hematite carries the self-reversed remanence. This study marks the second time that a naturally occurring self-reversed magnetization has been attributed to this mechanism and marks the oldestreportedinstanceof anytypeof self-reversedremanence.Themartitethatformsthrough thisprocess has the ability to retain a record of the negative exchange coupling from the time of its formation for hundreds of millions of years.

Four studies were conducted to examine whether cognitive appraisals, manipulated through task instructions, would moderate social-facilitation effects. In Study 1, participants in the challenge condition performed better on a mental arithmetic task when the experimenter was present. Conversely, participants in the threat condition performed worse when the experimenter was present. Study 2 extended these findings across 2 math tasks that varied in degree of difficulty. The pattern of performance data failed to support prior drive theories and provided support for a unique contribution of cognitive appraisals in explaining social-facilitation effects. Study 3 validated the appraisal manipulations by using multiple measures of cognitive appraisals. Finally, Study 4 offered increased validity by replicating the performance data using an anagram task.

The magnetic behaviour of magnetite at low temperatures is dominated by its transformation to a monoclinic crystal structure that is simultaneously ferrimagnetic, ferroelastic and ferroelectric below ∼ 125 K (the Verwey transition). Here we use electron microscopy to reveal the relationship between ferrimagnetic and ferroelastic domain structures in monoclinic magnetite. We present dynamic observations of magnetite during heating and cooling across the Verwey transition, revealing a diversity of unexpected interaction phenomena between crystallographic twins and magnetic domain walls. This study provides a new understanding of the low-temperature magnetic properties of magnetite that will affect a broad range of rock magnetic studies, from the interpretation of magnetic remanence in terrestrial rocks and sediments to the search for biogenic magnetite in extraterrestrial materials.

The Middle-Eastern copper slag is a promising new material for studying intensity variations in the geomagnetic field with high resolution and precision. The purpose of this study is to test the accuracy of archaeointensity estimates determined using copper slag by addressing two questions: 1) “Does slag material display the magnetic properties required for valid Thellier experiments?” and 2) “What is the accuracy of the archaeointensity estimates derived from Thellier-style experiments on optimal samples?” We address the first question through a comprehensive microscopic and magnetic study of representative archaeological slag samples in order to identify the properties responsible for optimal behavior in Thellier experiments. To address the second question, we reproduced slag samples in the laboratory under controlled magnetic fields and analyzed them using the same IZZI paleointensity technique used for the ancient slag. Microscopic analyses of the archaeological slag show that ferromagnetic phases occur as three-dimensional dendritic structures whose branches consist of submicron-elongated particles. Magnetic analyses show that these dendrites behave as an assemblage of shape-controlled, single-domain-like particles and that their magnetization is thermoremanent. We conclude that slag material can be magnetically suitable for valid Thellier experiments. The laboratory-produced slag material demonstrated similar magnetic and mineralogical properties as the archaeological slag. IZZI experiments showed that non-linear TRM acquisition, even at field strengths similar to Earth's, and TRM anisotropy are important factors to monitor during paleointensity studies of slag material. Anisotropy and non-linearity are probably related to the dendritic shape of the oxide grains. Intensity estimates derived from three laboratory-produced slag samples demonstrated accuracy to within ∼ 5% after applying the required corrections.

In this study, we examine the effects of reheating on finely exsolved hematite-ilmenite intergrowths from the ~91 Ma Ecstall pluton using reflected light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). As a result of the emplacement of the younger adjacent ~52 Ma Quottoon pluton, samples closer to a thermal boundary have experienced greater degrees of thermal alteration. Five main microstructural features characterize hematite-ilmenite intergrowths from the Ecstall: (I) exsolution lamellae of hematite and ilmenite; (II) oxidation of ilmenite to form hematite, rutile, and other Ti-rich phases; (III) 20–50 nm magnetite precipitates in hematite; (IV) rutile blitz texture; and (V) exsolution of hematite in rutile. Based on spatial relationships, textures II through V appear to be related to reheating of the Ecstall by the Quottoon, and samples up to ~14 km from the thermal boundary intrusive contact have been affected. We propose a mechanism, similar to that of Kontny and Dietl (2001), in which reheating has driven T - f O2 conditions across the hematite-magnetite buffer to lower f O2 resulting in the reduction of hematite. Higher temperatures also enhanced oxidation in ilmenite. The formation of magnetite altered the bulk magnetic properties of these samples, increasing NRM intensity. This study underscores the need to consider a pluton’s post-emplacement thermal history before making tectonic interpretations based on paleomagnetic data.

Magnetic minerals are ubiquitous in the natural environment, and they are also present in a wide range of biological organisms, from bacteria to human beings. the last ten years have seen a striking improvement in our ability to detect and image the magnetization of minerals in geological and biological samples. these minerals carry a wealth of information encoded in their magnetic properties. Mineral magnetism (together with the related disciplines of rock magnetism, paleomagnetism, environmental magnetism, and biomagnetism) decodes this information and applies it to an ever increasing range of geoscience problems, from the origin of magnetic anomalies on Mars to quantifying variations in earth's paleoclimate.

When suspended in solution, clay platelets coated with nanometer-scale magnetite particles behave as magnetorheologic fluids that are important to a variety of industrial applications. Such dual-phase assemblages are also similar to natural aggregates that record the direction and intensity of the Earth’s magnetic field in lake and marine depositional environments. This study characterizes the mineralogical structure and magnetic behavior of montmorillonite platelets coated with aggregates of nanometer-scale magnetite crystals. The distribution of magnetite crystal sizes in three different clay-magnetite assemblages was directly measured using conventional transmission electron microscopy and agrees within error with estimates derived from magnetic hysteresis measurements. Magnetic hysteresis and low field susceptibility measurements combined with electron holography experiments indicate that all three samples behave superparamagnetically at room temperature, and show increasing levels of single domain behavior as the samples are cooled to liquid nitrogen temperatures. At such low temperatures, magnetostatic interactions are observed to partially stabilize otherwise superparamagnetic grains in flux closure structures.

Participants (N = 151) rated a fictitious student who may have cheated on an exam. The student's description varied on prior academic performance (low achieving, average achieving, or high achieving) and exam grade (65 or 95). Participants' attitudes were most negative toward the low-achieving student who was also most likely to be perceived as cheating. However, participants recommended harsher punishments for students who scored a 95 regardless of prior academic achievement. Finally, a significant interaction indicated more negative attitudes and a harsher punishment for the “inconsistent student” (i.e., the student whose prior academic achievement did not match the current grade on the exam).

Impressions in a basaltic tuff located around Valsequillo Reservoir near Puebla, Mexico, have been interpreted as human and animal footprints along an ancient lakeshore, and are cited as evidence of the presence of humans in North America at 40 ka B.P. In this paper, we present new data that challenge this interpretation. Paleomagnetic analyses of the Xalnene Tuff, and lavas from the volcano from which it erupted, yield fully reversed magnetic polarities, indicating that the tuff was deposited prior to the last geomagnetic reversal (the BrunhesMatuyama ca. 790 ka). 40 Ar/ 39 Ar dating of Xalnene lapilli and lava from the source volcano yields indistinguishable ages of ~1.3 Ma, consistent with a period of reversed magnetic polarity (C1r.2r). Additional paleomagnetic measurements of individual millimeter-size lapilli indicate that the pyroclastic grains within the Xalnene Tuff have not been disturbed or rotated since their initial deposition, thereby ruling out the possibility that the tuff was reworked by wave action along the shores of an ancient lacustrine environment. This and other evidence indicate that the marks observed in the stone quarry site are not human ichnofossils.

Magnetized rocks can record the history of the magnetic field of a planet, a key constraint for understanding its evolution. From orbital vector magnetic field measurements of Mercury taken by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft at altitudes below 150 kilometers, we have detected remanent magnetization in Mercury's crust. We infer a lower bound on the average age of magnetization of 3.7 to 3.9 billion years. Our findings indicate that a global magnetic field driven by dynamo processes in the fluid outer core operated early in Mercury's history. Ancient field strengths that range from those similar to Mercury's present dipole field to Earth-like values are consistent with the magnetic field observations and with the low iron content of Mercury's crust inferred from MESSENGER elemental composition data.

This chapter describes the current state of the art in the field of computational and experimental mineral physics, as applied to the study of magnetic minerals. This chapter is divided into four sections, describing new developments in the study of mineral magnetism at the atomic, nanometer, micrometer, and macroscopic length scales. We begin with a description of how atomistic simulation techniques are being used to study the magnetic properties of mineral surfaces and interfaces and to gain new insight into the coupling between cation and magnetic ordering in Fe–Ti-bearing solid solutions. Next, we review the theory of off-axis electron holography and its application to the study of magnetotactic bacteria and minerals containing nanoscale transformation-induced microstructures. Then, we review the theory and application of micromagnetic simulations to the study of nonuniform magnetization states and magnetostatic interactions in minerals at the micrometer length scale. Finally, we review recent developments in the use of macroscopic magnetic measurements for characterizing and quantifying the microscopic spectrum of coercivities and interaction fields present in rocks and minerals.

The preferred orientation of plagioclase and pyroxene in gabbronorites from the Bushveld layered igneous intrusion (South Africa) was investigated using electron backscatter diffraction. In two localities 200 km apart (Belfast and Rustenburg) strong preferred orientation was observed with the principal fabric features aligned in the subhorizontal foliation plane (defined by (010) planes of plagioclase and (100) planes of pyroxene). The pattern appears to result from the orientation of tabular crystals during the dynamic intrusion events that formed the layered structure. Primary magmatic oxides are also influenced by the preferred orientation of plagioclase, generating an oblate magnetic susceptibility fabric parallel to the foliation plane. Plagioclase preferred orientation gives rise to other directionally dependent geophysical properties including a large seismic anisotropy with p-waves traveling 4–8% faster in the vertical than in the horizontal direction.

Evaluation–apprehension and distraction–conflict have typically been treated as alternative explanations for social facilitation. The present study tested both theories under a single design. The study examined (a) whether each explanation predicted social-facilitation performance outcomes and (b) whether combining evaluation and distraction manipulations produced even greater performance outcomes. The present study also explored whether physical presence is necessary to produce social-facilitation effects when evaluation and distraction manipulations are already present. The study found significant facilitation effects on the simple task only in the evaluation–apprehension condition. Significant performance impairment was found for both evaluation and distraction. Combining evaluation with distraction led to greater effects only on the complex task. Furthermore, physical presence does not appear necessary to produce social-facilitation effects.

The Permian–Triassic transition was an important time for many marine groups, including echinoderms. However, the fossil record of ophiuroids through this interval is poorly understood. Recent discoveries in Lower Triassic rocks from northern Italy and western US suggest that ophiuroids were more common during this time than previously has been appreciated. Evidence from resting traces (Asteriacites lumbricalis) indicates that Early Triassic ophiuroids lived on fine-grained siliciclastic sediments in oxygenated, shallow-marine environments within storm wave base. No resting traces have been recorded from deeper and/or oxygen-restricted settings. However, following death and decay, ophiuroid skeletal elements sometimes were transported into offshore, low-oxygen environments. All known occurrences of Early Triassic ophiuroids fall within the paleotropics, but this is attributed to sampling bias. Articulated body fossils and their trace fossils are most common in latest Lower Triassic (Olenekian) rocks, but disarticulated ossicles occur throughout the Induan and Olenekian. At times and places, ophiuroids were the dominant marine benthos, carpeting the substrate in prodigious numbers. However, at other times, they also comprised minor components of diverse benthic assemblages, living alongside crinoids (Holocrinus), bryozoans, bivalves, gastropods, and brachiopods. Morphological comparison with extant ophiuroids suggests that all known Early Triassic taxa were small surface-dwellers.

Crystallographic relationships between exsolved phases and their hosts are typically characterized using transmission electron microscopy (TEM) or single crystal X-ray diffraction (XRD). In this investigation, electron backscatter diffraction (EBSD) was used to determine the epitaxial relationships of exsolved laths of magnetite in clinopyroxenes from three sampling sites in the Cretaceous Messum Complex of Namibia. Two orientations of magnetite inclusions are found with their long axes subparallel to [100] and [001] of the host clinopyroxene. Inclusions subparallel to [100] c have [110] m // [010] c , (111) m // (101) c , and [112] m // [101] c . Inclusions subparallel to [001] c have [110] m // [010] c , (111) m // (100) c , and [112] m // [001] c . The EBSD-derived orientation relationships agree well with previous TEM and XRD studies on similar materials. The crystallographic relationships obtained with EBSD are used in conjunction with optimal phase boundary theory to determine the exsolution temperature of the magnetite inclusions, which is of importance to paleomagnetic studies. For one sample, this temperature (840 ′ 50 °C) can be compared with that (865 ′ 25 °C) derived from a more widely used cation exchange geothermometer. Thus it appears clear that exsolution occurred well above the Curie temperature of pure magnetite (580 °C).

[1] Crystallographically oriented and highly elongate magnetite inclusions in clinopyroxene are the dominant source of highly stable remanent magnetization in gabbros of the Early Cretaceous Messum Complex, Namibia. Rock magnetic properties determined for individual pyroxene crystals indicate a high proportion of single-domain magnetite, consistent with the observed sizes and shape anisotropy of the magnetite inclusions. As in previous studies of similar inclusions, these are inferred to have formed by exsolution. Two arrays of inclusions are regularly present in the Messum clinopyroxenes, inclined at about 74°, consistent with formation at about 800°C deduced from optimization of phase boundary orientations. Virtual geomagnetic poles from these rocks are consistent with reference data, confirming that the magnetization is of thermoremanent origin. Bipolar magnetizations are recorded at one site as well in individual clinopyroxene crystals, suggesting that remanence acquisition upon initial cooling of the gabbro spanned a geomagnetic polarity reversal.

The interpretation of satellite magnetic information (Magsat, Oersted, CHAMP, Swarm) requires the understanding of the mineralogy of crustal and mantle sources. Also, spectral analysis of magnetic data over forearcs and cratons calls for upper mantle contribution. The prospect of such a contribution contradicts the view that the mantle is too hot and its magnetism is too weak to influence magnetic anomalies.Here we examine the rock magnetic properties of fresh mantle xenoliths from four settings across the United States: phlogopite-spinel dunites from the Bearpaw Mountains, Montana, and lherzolites/harzburgites from San Carlos, Arizona; Kilbourne Hole, New Mexico; and Knippa, Texas. Paleomagnetic results show single-component natural remanent magnetizations (NRMs), which, combined with optical and secondary electron microscopy support the lack of post-eruption alteration and absence of host-rock contamination. The NRM carriers include magnetite at Bearpaw Mountain and San Carlos, and pyrrhotite at Kilbourne Hole and Knippa. These four areas show continental crust of distinct thicknesses and various geotherms. The potential mantle contribution to magnetic anomalies is forward modeled using crustal thickness, current geotherm and average magnetic properties of xenoliths. The San Carlos and Kilbourne Hole mantle, situated near the Rio Grande Rift is too hot and its magnetism is too weak to contribute to anomalies. The sulfide-dominated assemblage at Knippa does not support magnetization at mantle depths. In contrast, the Bearpaw Mountains combine a relatively cold geotherm (craton) and abundance of magnetite formed at mantle depth. This cratonic mantle, metasomatized by fluids from the Farallon plate, may contribute to long wavelength magnetic anomalies. © 2014 Elsevier B.V., Craton

Lithic residue analysis is traditionally based upon the morphological identification of microresidues preserved on the surfaces of stone tools. In order to improve the reliability of these identifications, we apply multiple techniques beyond morphological description to characterize the residues on stone tools from Hummal, Syria. We first document the residues using visible light microscopy and scanning electron microscopy, and then characterize them using energy dispersive X-ray spectroscopy, Fourier Transform Infrared microscopy, and confocal Raman microscopy. Our analyses confirm that some of the residues are bitumen. X-ray diffraction analysis of associated sediments is used to identify the other residues.

[1] The evolution of magnetization within a floodplain soil begins with initial deposition of magnetic particles during sedimentation and continues via subsequent alteration and growth of iron-bearing compounds by pedogenic and biologic processes. Measurements of soil magnetic properties capture information about the developmental history of the soil and are a convenient method by which to investigate environmental change and pedogenesis. Using a range of magnetic measurements, a comprehensive scenario for soil development was constructed for floodplain sediments at the Debra L. Friedkin site, an important archeological site near Buttermilk Creek, Texas. Floodplain deposits have traditionally been avoided for soil magnetism studies because it is thought that the episodic input of sediment would form soils characterized by discrete sedimentary units rather than a continuous record of pedogenesis. We demonstrate that alluvial deposits can sometimes carry a straightforwardly interpretable magnetic signal similar to those typically seen in loess deposits. Smooth variation of rock magnetic parameters as a function of depth also leads us to conclude that the soil at this site is largely undisturbed and that the age of lithic artifacts found within the soil may be interpreted within stratigraphic context.

[1] The magnetic properties of olivine-hosted Fe-Ni particles have been studied to assess the potential of “dusty olivine” to retain a pre-accretionary remanence in chondritic meteorites. Both body-centered (bcc) and face-centered cubic (fcc) Fe-Ni phases were formed by reduction of a terrestrial olivine precursor. The presence of Ni complicates the magnetic properties during heating and cooling due to the fcc-bcc martensitic transition. First-order reversal curve (FORC) diagrams contain a central ridge with a broad coercivity distribution extending to 600 mT, attributed to non-interacting single-domain (SD) particles, and a “butterfly” structure extending to 250 mT, attributed to single-vortex (SV) states. SD and SV states were imaged directly using electron holography. The location of the SD/SV boundary is broadly consistent with theoretical predictions. A method to measure the volume of individual SD particles using electron holography is presented. Combining the volume information with constraints on coercivity, we calculate the thermal relaxation characteristics of the particles and demonstrate that the high-coercivity component of remanance would remain stable for 4.6 Ga, even at temperatures approaching the Curie temperature of pure Fe. The high coercivity of the particles, together with the chemical protection offered by the surrounding olivine, is likely to make them resistant to shock remagnetization, isothermal remagnetization and terrestrial weathering, making dusty olivine a credible recorder of pre-accretionary magnetic fields.

Paleomagnetic studies of the 91 Ma Ecstall pluton and other Cretaceous plutons of British Columbia imply large northward tectonic movements (>2000 km) may have occurred during the tectonic evolution of western North America. However, more recent studies have shown that the eastern edge of the Ecstall pluton experienced considerable mineralogical changes as younger Eocene plutons, such as the ∼58 Ma Quottoon Pluton, were emplaced along its margins. We investigated changes in the rock magnetic properties associated with this reheating event by examining isolated grains of intergrown ilmenite and hematite, the primary paleomagnetic recorder in the Ecstall pluton. Measurements of hysteresis properties, low-temperature remanence, and room temperature isothermal remanent magnetization acquisition and observations from magnetic force microscopy and off-axis electron holography indicate that samples fall into three groups. The groups are defined by the presence of mineral microstructures that are related to distance from the Quotoon plutonic complex. The two groups closest to the Quottoon Pluton contain magnetite within hematite and ilmenite lamellae. Reheating of the Ecstall pluton led to an increase in coercivity and magnetization, as well as to development of mixed phase hysteresis. These results indicate that shallow paleomagnetic directions from the western Ecstall pluton are not affected by reheating and are therefore likely to record original field conditions at the time of pluton emplacement. In the absence of structural deformation, these shallow inclinations are consistent with large-scale northward translation suggested by the Baja–British Columbia hypothesis.

Domain wall pinning in titanomagnetite has been investigated at low temperatures using first-order reversal curve (FORC) diagrams, AC magnetic susceptibility, and Lorentz transmission electron microscopy. A discontinuous transition from a low-coercivity extrinsic pinning regime to a high-coercivity intrinsic pinning regime is evident in low-temperature FORC diagrams on cooling from 100 to 50 K. Intrinsic pinning is characterized by a “crescent moon” FORC distribution with narrow coercivity distribution centered on 10–20 mT. This crescent-shaped FORC distribution is reproduced using a modification of Neel's (1955) one-dimensional theory of domain wall pinning in a random field. The pinning transition coincides with a thermally activated relaxation process (activation energy 0.13 ± 0.01 eV), attributed to electron hopping. The relaxation and intrinsic pinning are explained as a magnetoelastic aftereffect caused by enhancement of magnetocrystalline anisotropy due to rearrangement and localization of Fe2+−Fe3+ cations within the domain walls. This study provides experimental verification that Neel's theory is an appropriate quantitative framework for the analysis of FORC diagrams in multidomain titanomagnetite and suggests a potential method for the quantitative unmixing of multidomain signals from FORC diagrams in rock and environmental magnetic studies.

Compelling archaeological evidence of an occupation older than Clovis (~12.8 to 13.1 thousand years ago) in North America is present at only a few sites, and the stone tool assemblages from these sites are small and varied. The Debra L. Friedkin site, Texas, contains an assemblage of 15,528 artifacts that define the Buttermilk Creek Complex, which stratigraphically underlies a Clovis assemblage and dates between ~13.2 and 15.5 thousand years ago. The Buttermilk Creek Complex confirms the emerging view that people occupied the Americas before Clovis and provides a large artifact assemblage to explore Clovis origins.

We present new 40 Ar/ 39 Ar ages and palaeomagnetic directions from two re-examined sequences of basaltic lava flows on the island of Santo Antao, Cape Verde: Tarrafal and Agua Nova. We find no evidence for the fully-reversed, Brunhes age excursions reported in Knudsen et al., Earth Planet. Sci. Lett., 206, 199–214, 2003. At Tarrafal, complex geology, including repeated gravitational collapses and/or considerable erosion followed by in-filling of subsequent valleys by younger lavas, coupled with an insufficient number of dated reversely and normally magnetised flows, led earlier researchers to suggest a series of Brunhes age excursions. At Agua Nova, the use of single samples to determine palaeodirections resulted in sampling of anomalous reversed directions, creating apparent excursions. We report new palaeomagnetic directions from Agua Nova, based on multiple measurements per flow determined by both alternating field and thermal demagnetisation. All flows of Brunhes age have virtual geomagnetic pole latitudes > 60°. Our findings highlight the need for precise age constraints and a high sampling density of dated flows, with multiple directional results per flow, when using long lava sequences to reconstruct palaeofield behaviour.

Figure 8. Smoothing effects on LOESS smoothed FORC distributions for a natural sample of pure hematite. In Figure 8a, optimum smoothing range is shown in green. Figures 8b, 8c, and 8d correspond to smoothing factors 2, 6, and 10, respectively. Undersmoothing produces a distribution that is dominated by noise (Figure 8b). Oversmoothing produces a distribution that obscures the presence of noninteracting grains along Hu = 0 (Figure 8d). Using the optimization routine described in Figure 5, the ideal FORC distribution is SF = 6.

In this paper, we present a complete three-dimensional characterization of vortex core spin structures, which is important for future magnetic data storage based on vortex cores in disks and in wires. Using electron holography to examine vortices in patterned Permalloy devices we have quantitatively measured the in-plane and out-of-plane magnetization of a vortex core. Observed core widths and integrated phase shifts agree well with those derived from micromagnetic simulations. α

This review describes the current state of the art in the field of computational and experimental mineral physics, as applied to the study of magnetic minerals. The review is divided into four sections, describing new developments in the study of mineral magnetism at the atomic, nanometer, micrometer, and macroscopic length scales. We begin with a description of how atomistic simulation techniques are being used to study the magnetic properties of minerals surfaces and interfaces, and to gain new insight into the coupling between cation and magnetic ordering in Fe–Ti-bearing solid solutions. Next, we review the theory of off-axis electron holography, and its application to the study of magnetotactic bacteria and minerals containing nanoscale transformation-induced microstructures. Then, we review the theory and application of micromagnetic simulations to the study of nonuniform magnetization states and magnetostatic interactions in minerals at the micrometer length scale. Finally, we review recent developments in the use of macroscopic magnetic measurements for characterizing and quantifying the microscopic spectrum of coercivities and interaction fields present in rocks and minerals.

Paleointensity is one of the least deter­ mined parameters in geomagnetism, yet this information has the potential to address many fundamental geophysical problems that bear on the evolution of the Earth’s core and lower mantle. We test two important hy­ potheses that affect our understanding of how paleointensity has changed in Earth’s past: (1) the Mesozoic Dipole Low (MDL) hypoth­ esis and (2) the inverse relationship between geomagnetic polarity reversal rate and paleo­ intensity. We report paleointensity results determined using both the Coe modified Thellier method and the IZZI protocol on the medium­grained hornblende­biotite granite of the Middle Jurassic Shamrock batholith in the southern Singatse Range, western Nevada (USA). Previous zircon U­Pb dating gives an age of batholith emplacement at ca. 165.8 ± 0.4 Ma. This age estimate is coincident with a period of unusually high reversal frequency (~10 reversals/Ma) in the Middle Jurassic. Remanence in the Shamrock batholith is held primarily by exsolved submicron magnetite inclusions in plagioclase. The labora tory un­ blocking temperature range for the well­de­ fined thermal remanent magnetization is nar ­ row, between ~540 and 575 °C, and median destructive fields are between 40 and 50 mT, thus we infer that the age of rema nence ac­ quisition is approximated by the U­Pb age estimate for pluton emplacement. Two sets of quality criteria were used to assess the paleo­ intensity results. The first set yielded an 87% success rate while the second set using more stringent criteria resulted in only a 20% suc­ cess rate. Mean paleointensity values for the Shamrock batholith using the “loose” and “strict” quality criteria are 34.0 ± 6.4 µT (N = 13) and 33.6 ± 9.6 µT (N = 3) respectively, with errors reported at one standard deviation. After correction for both remanence anisot­ ropy and cooling rate, the mean values that pass “loose” and “strict” criteria are respec­ tively 17.9 ± 2.7 µT and 17.5 ± 2.6 µT. The uncorrected and corrected paleointensity values for the “strict” estimates yield respec­ tive mean virtual dipole moments (VDMs) of 62.7 ± 18 ZAm 2 (Z = 10 21 ) and 32.7 ± 4.9 ZAm 2 . The uncorrected value is within error of the VDMs reported for plagioclase grains isolated from ca. 160 Ma basalts from Ocean Drilling Program Site 801, however these values have an absolute difference ranging from ~6 to 20 ZAm 2 , while the corrected VDM value is more consistent with the esti­ mated average Jurassic field strength of ~29 ZAm 2 . Using a recent estimate for the long­ term stable field strength of ~42 ZAm 2 , our corrected values add further credence to both the MDL and the inverse relationship between geomagnetic polarity reversal rate and dipole moment hypotheses.

[1] Titanomagnetite inclusions in pyroxene and plagioclase are carriers of stable magnetic remanence in some slowly cooled rocks such as gabbros, anorthosites, granulites, and diorites. Needle-shaped inclusions with average dimensions of 1 × 1 × >25 μm form epitaxially by exsolution from their host silicate. Close examination of clinopyroxene-hosted inclusions reveals an internal microstructure, which consists of magnetite (Fe3O4) prisms and ulvospinel (Fe2TiO4) lamellae that formed as a result of phase unmixing during initial cooling. This internal structure exerts a profound influence on the magnetic remanence properties of each inclusion, primarily by transforming it from a multidomain grain into an assemblage of magnetostatically interacting single-domain prisms. Here we use off-axis electron holography to image the magnetization states of individual prisms and the magnetostatic interactions between them. We show that the inclusions exhibit both single-domain and collective magnetic states that depend primarily on the shape anisotropies of individual magnetite prisms, magnetostatic interactions between closely spaced prism stacks, and the shape anisotropy of the needle itself. Prisms that are separated by thick ulvospinel lamellae show uniformly magnetized and/or vortex states. In contrast, closely spaced magnetite prisms behave as multipart vortices or as long composite columns, whose strong net magnetization may not be related directly to the orientation and shape of either the needle or the constituent prisms. The overall remanence direction recorded by clinopyroxene crystals containing finely exsolved inclusions is a reflection of both the inclusions' elongation directions and the prism arrangements within them.

A report of human footprints preserved in 40,000-year-old volcanic ash near Puebla, Mexico (http://www.royalsoc.ac.uk/exhibit.asp?id=3616tip=1), was the subject of a press conference that stirred international media attention. If the claims (http://www.mexicanfootprints.co.uk) of Gonzalez et al. are valid, prevailing theories about the timing of human migration into the Americas would need significant revision. Here we show by 40Ar/39Ar dating and corroborating palaeomagnetic data that the basaltic tuff on which the purported footprints are found is 1.30+/-0.03 million years old. We conclude that either hominid migration into the Americas occurred very much earlier than previously believed, or that the features in question were not made by humans on recently erupted ash.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

A report of human footprints preserved in 40,000-year-old volcanic ash in Mexico is challenged in an online Brief Communication Arising. Announced to the press in July this year, if true the discovery would overturn current theories on the timing of human migration to the Americas (believed to be some 30,000 years later). Argon dating and palaeomagnetic analysis show that the surface on which the prints were found is about 1.3 million years old, making it unlikely that these were human as they would then pre-date the appearance of Homo sapiens in Africa by over a million years. Arising from: R. Dalton doi: 10.1038/news050704-4 (2005)10.1038/news050704-4 A report of human footprints preserved in 40,000-year-old volcanic ash near Puebla, Mexico ( http://www.royalsoc.ac.uk/exhibit.asp?id=3616&tip=1 ), was the subject of a press conference that stirred international media attention1. If the claims ( http://www.mexicanfootprints.co.uk ) of Gonzalez et al. are valid, prevailing theories about the timing of human migration into the Americas would need significant revision. Here we show by 40Ar/39Ar dating and corroborating palaeomagnetic data that the basaltic tuff on which the purported footprints are found is 1.30±0.03 million years old. We conclude that either hominid migration into the Americas occurred very much earlier than previously believed, or that the features in question were not made by humans on recently erupted ash.

In this study, we deformed samples cut from a single magnetite octahedron and used transmission electron microscopy (TEM) and magnetic measurements to experimentally verify earlier computational models of magnetic domain wall pinning by dislocations and to better understand the nature of dislocations in magnetite. Dislocations in magnetite have been of interest for many decades because they are often cited as a likely source of stable thermoremanent magnetizations in larger multidomain (MD) magnetite grains, so a better understanding of dislocation effects on coercivity in MD magnetite is crucial. TEM imaging shows, for the first time, domain walls sweeping through the magnetite sample and being pinned at dislocations. In agreement with theory, these findings demonstrate that domain walls are more strongly pinned at networks of dislocations than at single dislocations and that domain walls pinned at longer dislocations have higher microcoercivities than those pinned at shorter dislocations. This experimentally illustrates the ability of dislocations to increase the coercivity of larger multidomain magnetite grains. The observed values for microcoercivity and bulk coercivity are in reasonable agreement with theoretical calculations. Burgers vectors were determined for some dislocations to verify that they were in keeping with expected dislocation orientations. The dislocations were found to be primarily located on close-packed {111} planes within the magnetite. Deformation caused only a minor change in bulk coercivity, but first-order reversal curve diagrams show populations with increased coercivity not visible in hysteresis loops.