Abstract A marine sediment core from the western Mediterranean provides a new high-resolution 4500 year record of palaeomagnetic secular variation and relative palaeointensity. In 2013, the 7.1 m C5 core was recovered from the Tyrrhenian Sea as part of the NextData climate data project. The coring site, 15 km offshore from the Volturno river mouth, is well located to record combined marine and terrestrial palaeoclimatic influences, and the fine-grained, rapidly deposited sediments are effective palaeomagnetic recorders. We investigate the palaeomagnetic field direction and strength recorded in the core, which provide a valuable high-resolution record of Holocene geomagnetic variation in the area. Using rock magnetic techniques, we constrain the magnetic mineralogy of the studied sediments and confirm their suitability for palaeomagnetic analysis. Palaeomagnetic declination and inclination records were determined by stepwise alternating-field demagnetization, and relative palaeointensity estimates were obtained based on normalization to anhysterestic and isothermal remanent magnetization and to magnetic susceptibility. The age of the core is well constrained with a tephra and biostratigraphic age model, and its magnetic records are compared with relevant core and model data for the region, demonstrating that our record is compatible with previous results from the area. An automated curve matching approach is applied to assess the compatibility of our data with the existing secular variation path for the Mediterranean area.

The Mesozoic and Paleogene pelagic carbonate rocks of the Northern Apennines have proved to be a fertile source for paleomagnetic research. Investigations of the magnetic properties of the Scaglia limestones illuminated the processes by which they were magnetized. Their directions of remanent magnetization contributed to an understanding of the geodynamic history of Adria as a promontory of the African plate and have been used to refine the Mesozoic part of the African polar wander path. Magnetic stratigraphy in the Umbrian sequence and in similar facies in the southern Alps has established an independent record of geomagnetic polarity history since the Middle Jurassic. Correlation with the record derived from interpretation of oceanic magnetic anomalies mutually confirmed the global nature of the polarity history. This enabled the dating of plate motions and the development of a geomagnetic polarity time scale for the late Mesozoic and Cenozoic.

The eruptive history of the Shatsky Rise, a large oceanic plateau in the northwestern Pacific Ocean, is poorly understood. Although it has been concluded that the Shatsky Rise volcanic edifices erupted rapidly, there are few solid chronological data to support this conclusion. Similarly, the Shatsky Rise is thought to have formed near the equator, but paleolatitude data from the plateau are few, making it difficult to assess its plate tectonic drift with time. To understand the formation history of this oceanic plateau, paleomagnetic measurements were conducted on a total of 362 basaltic lava samples cored from the Shatsky Rise at 4 sites (U1346, U1347, U1349, and U1350) during Integrated Ocean Drilling Program Expedition 324. Examining changes in paleomagnetic inclinations, we gain a better understanding of eruptive rates by comparison of observed shifts in inclination with expected paleosecular variation. At three sites (U1346, U1347, and U1349) little change in paleomagnetic directions was observed, implying that the cored sections were mostly erupted rapidly over periods of <~100–200 yr. Only Site U1350 displayed directional changes consistent with significant paleosecular variation, implying emplacement over a period of ~1000 yr. The paleomagnetic data are consistent with the idea that the Shatsky Rise igneous sections were mostly emplaced rapidly, but there were some time gaps and some fl ank locations built up more slowly. Because paleosecular variation was inadequately sampled at all the Shatsky Rise sites, paleolatitudes have large uncertainties, and because of the equatorial location, magnetic polarity is also uncertain. All sites yield low paleolatitudes and indicate that the Shatsky Rise stayed near the equator during its formation. Given that the locus of magmatism moved northward relative to the Pacific plate while staying near the equator, the Pacific plate must have drifted southward relative to the spin axis during the emplacement of the plateau.

Abstract The Indo-Myanmar Ranges (IMR) of NE India are host to various ophiolitic rocks, including metamorphosed Alpine-type harzburgite and lherzolite. Compared to abyssal peridotites of normal oceanic lithosphere, these ultramafic rocks are enriched in trace and rare earth elements. Spilitic pillow lavas along with mafic dykes and sills locally intruded into the serpentinized ultramafic rocks and associated pelagic sediments exhibit alkaline compositional affinities. Ophiolite formation and emplacement were by a process analogous to that described for mantle exhumation in hyper-extended continental margin settings and ophiolites in parts of the European Alps, involving very slow passive continental margin rifting accompanied by slow upwelling or extensional unroofing of the subcontinental upper mantle up to the seafloor. Preliminary palaeomagnetic measurements conducted on ultramafic rocks within the IMR ophiolite belt give a virtual geomagnetic pole (VGP) at 47° N, 045° E for thermal demagnetization (TDM) measurements and 33° N, 013° E for the alternating field demagnetization (AfD) measurements, requiring an anticlockwise rotation of the ultramafic bodies by 14° during the subduction process. The original trend of the spreading axis of the ophiolites was probably NE–SW, with spreading directed NW–SE. Computation of palaeolatitude of the ultramafic rocks gives an average value of 24.67°. Comparison between the palaeolatitude and the present latitude of the sample sites provides a mere latitudinal shift of less than 1°. Field studies, combined with an analysis of structural and tectonic features in the IMR, suggest a generalized WNW–ESE (east–west) compression and NNE–SSW (north–south) extension contradictory to the NNE–SSW contraction indicated by seismic data. Area balancing techniques employed along sections orientated perpendicular to regional tectonic strike in the IMR reveal systematic variations in the amount of crustal shortening, with a maximum of approximately 60% recorded in the Nagaland–Manipur segment along 25.644° N, 93.826° E–25.076° N, 95.897° E. The amount of shortening gradually decreases away from the axis of maximum shortening and on both sides. Calculations of relative plate motion based on rotation vectors given by different workers for various plate pairs represented in the region reveal that the interaction between the Indian and Myanmar plates can ideally produce the structural and tectonic features of this range. Dextral shear coupled to oblique subduction of the Indian Plate below the Myanmar Plate can best explain all of the structural and tectonic features present in the IMR.

A detailed total intensity magnetic survey of a local negative magnetic anomaly located in the southern sector of the inner ring in the Ries impact structure was carried out in 2006–2007. As the suevite of the Ries crater is known to have an often strong reverse remanent magnetization causing negative magnetic anomalies, a suevite body lying below shallow lake sediments upon the crystalline basement rocks of the inner ring was suspected to be the cause of the anomaly. A drilling program conducted by the Geological Service of Bavaria offered the opportunity to drill a 100-m-deep core hole into this anomaly in 2006. The core stratigraphy involves from 0 to 4.5 m fluviatile Quaternary lake sediments, from 4.5 to 21 m Neogene clays of the Ries crater lake, and from 21 to 100 m suevite and impact melt rock. The suevite and the impact melt rock have a strong reverse remanent magnetization and very high Koenigsberger ratios. Thermomagnetic and coercivity analyses indicate that magnetite is the dominant carrier of the magnetization. The borehole unfortunately did not penetrate the crystalline basement rocks of the inner ring, but modeling of the magnetic source body indicates that the bottom of the hole could not be far from the contact. A macroscopic survey shows suevite from 21 to 87 m, highly diverse in terms of suevite types, and a gradational transition to massive impact melt rock constituting the lowermost 13 m of the drill core. A detailed macroscopic description and first results of microscopic observations reveal that suevite groundmass is substantially altered to secondary phyllosilicates (mostly smectite, minor chlorite) and locally extensive development of calcite. Crystalline basement–derived lithic clasts and minerals dominate the clast population, and only traces of clastic material derived from the upper sediment parts of the target could be recorded. Macroscopically and microscopically, melt fragments have mostly irregular shapes, which lead to the tentative conclusion that only part of the melt—and by implication suevite—mass is derived from fallout of the ejecta curtain. On the other hand, most melt fragments and larger lithic clasts are seemingly oriented subperpendicular to the core axis. This could be interpreted as being due alternatively to settling through air or lateral movement within the actual crater. The gradational zone between proper suevite and massive impact melt rock is characterized by increasing enrichment of melt component and concomitant reduction of suevitic groundmass, until in the uppermost impact melt rock, only millimeter-wide stringers of groundmass remain between densely packed centimeter- to decimeter-size melt fragments.

The Archean granites of the Vredefort impact structure show a high intensity of natural remanent magnetization (NRM) and a random dispersion of directions of high-coercivity components on the centimeter scale. It has been suggested that this anomalous remanence is carried by rod-shaped single-domain (SD) magnetites along planar deformation features (PDFs) in shocked quartz produced as a consequence of the impact event. To determine the carriers of this NRM, we conducted surface magnetic field observations using scanning magneto-impedance (MI) magnetic microscopy during stepwise alternating field (AF) demagnetization over a 1-mm-thick slice of Vredefort granite. We found that the stable component after demagnetization gives rise to just three strong magnetic anomalies. Progressive thinning of the scanned section and micro-Raman spectroscopy revealed that the source of these magnetic anomalies, the highly coercive remanence-carrying mineral, is an assemblage of relatively coarse-grained (1–200 μm) magnetite in biotite, not single-domain magnetite embedded along PDF lamella.