Igor Túnyi

Paleomagnetism of Jurassic sediments as evidence for oroclinal bending of the Inner West Carpathians

Abstract The Jurassic carbonates from the Krizna Nappe contain a pre-tectonic characteristic component of remanence. The declinations for individual nappe fragments differ, and form a fan-like pattern. They are close to the tectonic vergencies measured in the field, which suggests that the arcuate structure of the Inner Carpathians results from an oroclinal bending of an originally straight belt.

Palaeomagnetic results from the fold and thrust belt of the Western Carpathians: An overview

Abstract The Western Carpathians are separated into an Outer and Inner Carpathians (both comprising several nappe systems) by the extremely narrow and highly deformed Pieniny Klippen Belt. The main phase of deformation and thrusting took place during the Late Cretaceous in the Inner Carpathians, at the end of Cretaceous–Paleocene in the Pieniny Klippen Belt and in the Miocene in the Outer Carpathians. In this paper a large amount of palaeomagnetic results of different quality available from several nappe stacks and from overstep sequences were reviewed and interpreted in terms of tectonics. The data suggest that all three main units participated in two phases of anticlockwise rotation starting at 18.5 Ma, that is, the Outer Carpathian nappes in front of the already consolidated Alpine–Carpathian–Pannonian block became accreted to the block. Late Cretaceous nappe transport, Neogene uplift of ‘core mountains’ and possibly oroclinal bending of pre-Oligocene age can account for important differences in pre-Cenozoic palaeomagnetic declinations. Most of them exhibit less or no anticlockwise rotation suggested by the overstep sequences, implying pre-Cenozoic clockwise rotations of variable angles.

Magnetic variations excited by a radial magnetic dipole located in the earth's core

SummaryTheoretical formulae are derived for computing a variable magnetic field, excited by a harmonically oscillating radial magnetic dipole (RMD), located eccentrically at the surface of the Earths core. By numerical computations, using a three-layered conductivity model of the Earth, it is proved that the field due to this source, computed for the surface of the Earth, is relatively weak in comparison to the field of a stationary magnetic dipole, provided the period of the changes is less than 500 years. The “zone of influence” of the RMD at the Earths surface is also determined and on its basis a number of conclusions were drawn with respect to representing the non-dipole part of the geomagnetic field by means of the RMD system in the Earths core.

Magnetic variation generated by a tangential magnetic dipole located in the Earth's core

SummaryThe harmonically variable magnetic field, generated by a tangential magnetic dipole (TMD), located eccentrically at the surface of the Earths core, is investigated for various periods of time variations and for a three-layer conductivity model of the Earth. Numerical computations have shown that the field is inductively damped for variation periods of less than 500 years as compared to the field of a static TMD. It is proved that the field appropriate to the TMD, has a more complicated distribution of the Earths surface than the field of a radial magnetic dipole. Comparison with maps of the non-dipole part of the geomagnetic field shows that the TMD is not as suitable for interpreting the observed non-dipole field and its variations as the eccentric radial magnetic dipole.

Effects of and methods for determination of induced magnetic anisotropy of igneous and metamorphosed rocks

The phenomena of the magnetic memory of rocks associated with paleointensity, paleotemperature, and paleostress are reviewed and discussed here. The methods for the determination of the paleointensity and the paleoconditions are described and discussed in terms of their sensitivity and applicability. The determination of paleoconditions (stress and temperature) is essential for understanding rock mineral formation and rock history. Such knowledge is applicable also in ore deposit geology and geophysics. The phenomena of the magnetic memory manifest themselves through the constriction and asymmetry in the hysteresis loops, as well as through a nonlinear pattern in the anhysteretic magnetization curve, both being due to the induced magnetic anisotropy. The pros and cons of some applied methods are reviewed. The superposition of several paleotemperatures (re-heatings of the rock) and/or paleostresses is studied also. Under certain conditions, a rock can remember information on several paleotemperatures (paleo-heating events), as well as the respective intensities of the geomagnetic field of the past.