Paleomagnetic data from the sheeted dike complex north of the Arakapas fault reveal significant internal rotations. The north-south-trending dikes have remanent magnetization directions close to the well-known westerly paleomagnetic direction of the Troodos massif, whereas the east-west-trending dikes near the Arakapas fault have northerly remanent magnetization directions. The paleomagnetic data are in agreement with the apparent clockwise rotation of the dikes. Contrary to recent geological analyses which postulate that the pattern of dike trends is due to dike injection into a sigmoidal stress field along a sinistral transform fault, the paleomagnetic results indicate clockwise rotations about vertical axes in response to a dextral shear. In addition to the rotations around vertical axes, small rotations around subhorizontal axes are inferred from the paleomagnetic data for tilted dikes. Thus, these data reinforce the vertical intrusion hypothesis.

Superparamagnetic iron oxide particles, a new class of contrast agents for MRI, are extremely good enhancers of proton relaxation. However, the development of such particle systems has resulted in a wide range of preparations whose physico-chemical properties differ greatly. We have conducted a set of physical experiments: X ray diffraction analysis, relaxivity measurements, susceptibility determinations, and thermomagnetic cycling on different preparations of superparamagnetic particles. Our results demonstrate a good correlation between susceptibilities measured in liquid samples at room temperature and the R2/R1 ratio. Susceptibility measurements between liquid nitrogen temperature and room temperature show three different types of behavior dependent on the size of iron oxide crystals. Comparison of heating and cooling curves from strong field thermomagnetic cycles provides information about the maghemite/magnetite crystal content. The information on magnetic properties reported in this study may help to characterize and to select these materials for use as MRI contrast agents.

The Silurian volcanism of the Almaden mining district, southern Spain, has been the object of a very detailed paleomagnetic study. The 175 cores (25 sites) sampled all along the eastern termination of the Almaden syncline were subjected to magnetic susceptibility measurements, thermomagnetic cycles, progressive alternating field and thermal demagnetizations as well as microscopic observations. The magnetic mineralogy of these volcanics flows is dominated by magnetite in at least two very distinct forms, including small cubic distributed grains and large elongated crystals. The observed anisotropy of magnetic susceptibility varies according to the relative abundance of the two magnetite phases, showing a complete inversion of the susceptibility tensors. This anisotropy has been related to the emplacement of the flows on a gentle slope dipping ∼ 10° toward the southwest, implying that their volcanic source was located to the northeast. The paleomagnetic analysis has revealed two characteristic components of magnetization: the first (direction D=109°, I=+11°, α95=9°, pole position at 11°S, 69°E, dp=5°, dm=9°) yields a negative fold test and is interpreted as a Late Paleozoic partial overprint; its declination is 46° away of the expected Late Paleozoic field direction, which confirms that rotations are still occurring after the main folding phases of the Variscan orogeny; the second (direction D=62°, I=−36°, α95=14°, pole position at 8°N, 118°E, dp=9°, dm=13°) is prefolding as evident from the significant clustering when applying appropriate tectonic corrections, and we interprete it as the original magnetization of Silurian age. The compilation of all Paleozoic paleomagnetic results from Spain reveals that the Iberian Meseta has been moving along with Gondwana at high drift rates throughout Ordovician and Silurian times.