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A quantitative correlation has been established between finite strain and the anisotropy of magnetic susceptibility (AMS) in sandstones of the Precambrian Chelmsford Formation of the Sudbury Basin, Ontario. Investigations of the progressive acquisition of isothermal remanent magnetization and its destruction with reverse field and thermal demagnetization as well as microscopic examination of polished thin sections show that both pyrrhotite and magnetite are present in the sandstone. Measurements of the AMS have been carried out at 16 sites distributed throughout the Chelmsford Formation outcrop. Considerable variation in the shapes of the magnetic susceptibility ellipsoids (axes k max > k int > k min exists within each site, with the k max and k int axes contained in the cleavage planes, where developed. The magnitudes of the magnetic susceptibility axes have been quantitatively correlated with strain measurements carried out by Clendenen et al. (this issue). Two different strain to magnetics correlations have been carried out: between the site mean strain determined using deformed concretions and the mean values of the AMS at each site, and between individual specimen strain values determined at the microscopic scale and the individual specimen AMS. In both cases, separate correlations were made between strain long, intermediate and short axes and their corresponding magnetic k max , k int , and k min axes. At 10 sites, the site mean strain values were derived from strain analysis of the concretions and at an additional 6 sites the site mean strain values were derived from the AMS to strain correlation. 527 individual cores were converted to equivalent strain values using the AMS-structural correlation of individual specimens. This study extends the use of AMS methods to include strain determination in sandstones, and provides an order of magnitude increase in the available number of such data for further structural analysis.

Anisotropy of magnetic susceptibility (AMS) was measured at 15 sites in deformed Helvetic limestones of the Morcles nappe in western Switzerland. Inverse magnetic fabrics, characterized by axes of maximum susceptibility subperpendicular to bedding or cleavage, were observed at four sites in the root zone of the nappe. Acquisition and thermal demagnetization of isothermal remanent magnetization show that the ferromagnetic mineralogy is dominated by pyrrhotite, with various proportions of magnetite, hematite and goethite. The matrix minerals were studied in thin section with a staining technique to distinguish different carbonates, by X-ray texture goniometry and by microprobe analysis. Observations of AMS at room and liquid nitrogen temperatures, and of the temperature dependence of bulk susceptibility, lead to the conclusion that the inverse fabrics result from a paramagnetic component due to Fe2+ ions in the calcite matrix.

More finite strain data has been obtained from autochthonous Permian mudstones of the Alpes Maritimes, S.E. France. These new data were computed from field measurements of green spots on all available sections, deformed mudcracks and from the quantitative correlation between magnetic susceptibility anisotropy and finite strain in these rocks. Previously published finite strain data and the new results are presented on a series of structural maps and cross-sections for the Dome de Barrot, the Tinee and Vionene region and the Roya region. As in previous studies difficulties arise in explaining the apparently variable extension parallel with the 100°, subhorizontal bedding-cleavage intersection: either this is real or there were large volume changes during the tectonic deformation. Study of quartz fibres, developed in deformed mudcracks in the Tinee valley, suggest that early in the tectonic history incremental stretching directions were parallel with the bedding—cleavage intersection, while later they were down-dip in the 100° trending cleavage. Since these Permian rocks have remained stuck to the Argentera basement they also record displacements and deformations in the basement. The early 100°, subhorizontal stretching is consistent with NW-SE dextral, strike-slip basement faulting, while later, down-dip stretching in the cleavage is consistent with contraction faults in the basement. This information and new palaeomagnetic data on the same samples are combined with recent geophysical evidence and regional tectonic studies, to provide a new precision to the tectonic history of this part of the Western Alpine External Zone.

Paleomagnetic investigations have usually been impossible in deformed rocks because of the effects of distortion on the remanent magnetization vector. Deformation produces a magnetic anisotropy in rocks which can deflect the remanence away from the minimum susceptibility axis. However, the assumption that the intersection points of great circles joining these two directions represent an improved estimate of the undisturbed remanence is invalid because the amount of the deflection of each remanence is not really known. Anisotropy of magnetic susceptibility (AMS) provides a quantitative basis for strain determination. The principal axes of the magnetic anisotropy ellipsoid have the same directions as those of the strain ellipsoid. A linear relationship between the normalized principal susceptibility differences and the logarithmic strains has been found in several rock types. If the correlation method used is valid, AMS observations can be used to establish the magnitudes and directions of the principal strains. Strain modifies bedding planes and realigns the grains that carry magnetic remanence. Compensation for deformation requires application of a modified bedding tilt correction and correction of the remanent vector for distortional strain. The effects of strain on bedding can be corrected using passive marker theory. Attempts to compensate for distortional strain by treating the remanent vector as a passive marker have proved inconclusive. During deformation linear and planar elements deflect away from the axis of maximum shortening. The passive marker correction shifts the remanent vectors toward the local shortening axis for the site and reduces the directional scatter. Tests of the passive marker method in strongly deformed rocks resulted in a remanence distribution dominated by the shortening axis directions. The passive marker model becomes inapplicable when the deformation results in recrystallization of the rock matrix.

The relationships among the anisotropy of magnetic susceptibility, the finite strain and the characteristic remanent magnetization (ChRM) have been investigated in deformed red sediments from the Alpes Maritimes in southeast France. The magnetic properties of these rocks are due to hematite. The finite strain is known from field studies of the shapes and orientations of green reduction spots and from optical microscopy and X-ray texture goniometry studies of chlorite and illite. The strain data permit a classification of the magnetic results according to four main stages of progressive deformation. In the compaction stage magnetic anisotropy is flattened in the bedding due to compactional loading; the ChRM directions approximate to a Fisherian distribution about a mean value close to the known Permian direction for the region. As deformation proceeds, pencil structure first develops and the anisotropy is characterized by a prolate pattern with maximum axis parallel to the subhorizontal azimuth of the pencil structure and fold axes. With increasing deformation the magnetic susceptibility ellipsoid becomes oblate and finally triaxial. At these stages of high deformation the anisotropy patterns show that the hematite grain orientations are strongly influenced by the cleavage. The remanence directions in deformed rocks do not correspond to a Fisher distribution and eventually deviate strongly from Permian directions. These results show that paleomagnetic vectors are affected by the distortional strains which accomodate shape change in the rock. Simple tilt correction without compensation for the strain would yield incorrect paleopole positions. An attempt has been made to compensate for the effects of deformation by regarding the remanent vector as a passive marker (March, 1932). Equations for strain removal were applied to the remanence in two ways; 1. (a) using strain data directly obtained in the field for each site and 2. (b) by converting the magnetic susceptibility anisotropy of each sample to a corresponding finite strain value. Correcting for the finite strain by both methods improves the within-site grouping of paleomagnetic vectors. In strongly deformed rocks strain removal assuming the March model results in overcorrection of the remanent magnetization data. In low-strain regions distortion may produce mechanical rotation of the hematite particles, but recrystallization may alter the deformation mechanism in regions of high strain. The limits of applicability of the passive marker treatment could not be tested adequately in the deformed red sediments of the Alpes Maritimes.

The Eower Cretaceous Maiolica formation was investigated in a regional paleomagnetic study in order to clarify the role of the Umbrian-Marches region in Western Mediterranean tectonics. This area has been considered as a semi-autonomous microplate by some authors and as an allochthonous overthrust block by others. Oroclinal bending has been inferred from earlier paleomagnetic results of the Scaglia formation. In spite of weak natural remanent magnetizations (NRM), stable characteristic remanent magnetization (ChRM) directions were defined for 31 sites. The site-mean directions are well-grouped ( D = 306°, I = 37°, α 95 = 5°) but are not uniform. Fisher statistics are therefore not applicable. The nonuniformity of directions is partially due to regional and local variations, but is not related to the orientation of the fold axes as suggested by several authors. It is possible that the Umbrian-Marches region has suffered thrust decollement on the underlying Triassic evaporites during the Late Tertiary orogeny, but this was not accompanied by large-scale translation or rotation relative to the assumed autochthonous parts of the Adriatic promontory.

A paleomagnetic study at 15 sites (315 samples) in Permo-Triassic red beds of the Helvetic nappes of eastern Switzerland isolated stable characteristic and secondary remanent directions. Thermal demagnetization and isothermal remanent magnetization experiments suggest pigmentary hematite carries the characteristic direction. Secondary directions are scattered but may have been acquired during the Alpine deformation in the Oligocene and Miocene. The characteristic directions also show large between-site scatter. Anisotropy of magnetic susceptibility indicates that the hematite grains are flattened within the slaty cleavage, and that there is a north-south lineation. This anisotropy pattern implies that the magnetic grains were realigned by the Alpine deformation. It is not possible to explain the characteristic remanent magnetization deviations on a site-by-site basis, but the site mean directions are streaked along a great circle, the down dip direction of which is approximately parallel to the regional fold axes (60°/20°). This spread could be explained by a penetrative simple shear deformation associated with the nappe-internal deformation.

A selection of paleomagnetic investigations in different fold belts shows that the data can only be reliably used for evaluation of curvature of the mountain arc when (a) they have been determined by the most rigorous laboratory and analytical techniques and (b) there is detailed information about the local tectonic setting of each sampling site. Early paleomagnetic results from Japan must be discounted because the samples were not demagnetized; more recent studies appear to imply deformations within Japan that are not observed in the field. Application of paleomagnetism in remote regions with difficult access like the Himalaya and the Antarctic is handicapped by the tectonic complexity of the regions and sparseness of available data. In high latitudes, moreover, large declination uncertainties reduce the interpretative value of the declination data. When the paleomagnetic and structural geological conditions are fulfilled, linear regression analysis can be applied to paleomagnetic declinations and the corresponding fold axis trends. The slope of the regression line can be tested with a t-statistic against zero slope (no oroclinal bending) or any chosen value, such as unit slope (originally straight fold belt). Paleomagnetic data suggest that oroclinal bending may have formed the Iberian arc in northern Spain, but they do not support oroclinal bending as the reason for the observed curvature of the Swiss Jura mountains or the Umbrian-Marches Apennines in Italy.

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 (

The carbonate platform margin of the Montagna della Maiella in the Abruzzi region of central Italy has a complex history of sedimentation, consisting of aggradational and progradational episodes along the shelf margin and pelagic deposition in the basin. A paleomagnetic study at 12 regionally distributed limestone sites of late Cretaceous to Miocene age in the Maiella anticline was unable to define stable magnetic directions at most sites, largely due to the weakness of the magnetizations. At the few usable sites inclinations agreed with reference values based on an African polar wander path. Declinations were inconsistent, indicating local tectonic rotations. Both normal and reversed polarities were preserved at some sites. A magnetostratigraphic section, consisting of 280 samples spaced at 1–1.5 m intervals, was sampled along a profile in the Valle delle Tre Grotte, near the village of Pennapiedimonte. Sequence stratigraphy, based on two-dimensional analysis of outcrops, formed the stratigraphic framework for the magnetostratigraphic study. Rock magnetic analyses showed that magnetite is the dominant ferromagnetic mineral in the limestones. Both alternating field and thermal demagnetization were satisfactory in defining two main components in the weak magnetizations. A component with low coercivity, low unblocking temperature and normal polarity was close in direction to the present axial dipole field direction at the site. A higher coercivity, higher unblocking temperature component with both polarities was interpreted as the characteristic remanent magnetization (ChRM). Although the mean directions of samples with normal and reversed polarity are not exactly antipodal, a stratigraphic sequence of magnetozones is very clearly defined. The Pennapiedimonte magnetostratigraphy correlates well with late Cretaceous Chrons C30r to C34n in the established polarity timescale; numerical ages can thus be allocated to the reversals. Correlation to the Gubbio section allows paleontological dates for the reversal sequence to be inferred. The correlations allow more precise dating of formational and sequence boundaries and a better evaluation of stratigraphic hiatuses. In particular, the boundary between the Tre Grotte Formation (Supersequence 1, Turonian to middle Campanian) and the Orfento Formation (Supersequence 2, upper Campanian to upper Maastrichtian) is shown to be associated with a significant hiatus, spanning most of the middle Campanian G. ventricosa zone. Likewise, the absence of Chron C29r at the top of the Orfento Formation (SS2) documents non-deposition during the latest Maastrichtian or

Iron is a central element in the metabolism of normal and malignant cells. Abnormalities in iron and ferritin expression have been observed in many types of cancer. Interest in characterizing iron compounds in the human brain has increased due to advances in determining a relationship between excess iron accumulation and neurological and neurodegenerative diseases. In this work, four different magnetic methods have been employed to characterize the iron phases and magnetic properties of brain tumour (meningiomas) tissues and non-tumour hippocampal tissues. Four main magnetic components can be distinguished: the diamagnetic matrix, nearly paramagnetic blood, antiferromagnetic ferrihydrite cores of ferritin and ferrimagnetic magnetite and/or maghemite. For the first time, open hysteresis loops have been observed on human brain tissue at room temperature. The hysteresis properties indicate the presence of magnetite and/or maghemite particles that exhibit stable single-domain (SD) behaviour at room temperature. A significantly higher concentration of magnetically ordered magnetite and/or maghemite and a higher estimated concentration of heme iron was found in the meningioma samples. First-order reversal curve diagrams on meningioma tissue further show that the stable SD particles are magnetostatically interacting, implying high-local concentrations (clustering) of these particles in brain tumours. These findings suggest that brain tumour tissue contains an elevated amount of remanent iron oxide phases.

Remotely controlled actuation with wireless sensorial feed-back is desirable for smart materials to obtain fully computer-controlled actuators. A light-controllable polymeric material is presented, in which exposure to light couples with a change in magnetic properties, allowing light signal conversion into non-volatile magnetic memory. The same material can serve, additionally, both as actuator and transducer, and allows the monitoring of its two-way elastic shape-changes by magnetic read-out. In order to tune the macroscopic magnetic properties of the material, both the reorientation of i) shape anisotropic ferrimagnetic nano-spindles and ii) a mechanically and magnetically coupled liquid-crystalline elastomer (LCE) matrix are controlled. These materials are envisioned to have great potential for the development of innovative functional objects, for example, computer-controlled smart clothing, sensors, signal encoding, micro-valves, and robotic devices.

Magnetic properties of a two-component system, consisting of horse spleen ferritin (HoSF) which contains a $5--8\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ sized antiferromagnetic ferrihydrite $(5{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}∙9{\mathrm{H}}_{2}\mathrm{O})$ core and ferrimagnetic magnetite $({\mathrm{Fe}}_{3}{\mathrm{O}}_{4})$ nanoparticles (MNP) with an average size of $10--20\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, have been investigated by using four different methods: induced magnetization versus (1) temperature and (2) field; (3) AC susceptibility; and (4) first-order reversal curves (FORC). All measurements were done on a mixed system of HoSF and MNP, as well as separately on the individual components. The average blocking temperature $({T}_{\mathrm{B}})$ of the mixed system at $50\phantom{\rule{0.3em}{0ex}}\mathrm{mT}$ is $15.6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which is a shift towards higher temperatures compared to pure HoSF $({T}_{\mathrm{B}}=12\phantom{\rule{0.3em}{0ex}}\mathrm{K})$. The contribution of the MNP component to magnetic ordering is evident only as a separation of the zero-field-cooled and field-cooled measurement curves. ac susceptibility is dominated by the ferrimagnetic MNP and shows strong frequency dependence. The peak ac susceptibilities can be described by the Vogel-Fulcher law, indicating the influence of interactions within the system. Hysteresis measurements at $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ show a wasp-waisted shape due to the mixture of a high coercivity phase (HoSF) with a low coercivity phase (MNP). Initial magnetization curves above ${T}_{\mathrm{B}}$ can be fitted by a sum of Langevin functions, showing superparamagnetic behavior of both components. FORC diagrams are effective in illustrating the change from that of blocked MNP particles together with the superparamagnetic HoSF at $20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ to purely superparamagnetic behavior in both components above $50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We conclude that the mixed nanoparticle system is a good model for complex natural samples, such as human brain tissue.