The natural remanent magnetizations of the exeter volcanic traps (Permian, Europe)

The natural remanent magnetizations of 35 samples from five quarries in the Permian traps from the Exeter region were carefully examined. A considerable number of the samples contained a secondary magnetism, the intensity of which was directly proportional to the susceptibility. This secondary magnetism (probably of viscous origin) was completely eliminated with a.c. magnetic fields up to 400 Oe. Only the samples from one quarry (Killerton) had in addition much harder secondary magnetism. Besides, all traps contained a harder remanent magnetization whose direction was similar in all samples and thus characteristic for these Exeter traps. This characteristic magnetization mostly was composed of a soft and a hard component. Both components differ very slightly in direction. The intensity of the soft characteristic magnetization did not vary much from sample to sample, but that of the hard characteristic magnetization varied inversely as that of the secondary (viscous) magnetization. When the unfolding test was applied to the mean characteristic magnetization directions of the localities the circle of confidence decreased from 17° to 6°, so this remanent magnetization was acquired before folding took place. It is supposed that this characteristic, pre-tilting remanent magnetization is the fossil primary remanence. It indicates a mean local geomagnetic field direction of D = 198°, I = −25°, corresponding to a virtual pole at 49.5°N 148.5°E. It is argued that during the Permian the virtual geomagnetic pole for Meso-Europe wandered in western direction towards its Triassic position on the east coast of Asia

The magnetism of some Permian red sandstones from northwestern Turkey

A series of eighteen oriented samples collected from the Permian of the Amasra region (Black Sea coast) revealed after progressive demagnetization a characteristic remanent magnetization vector with a declination of 290° and an inclination of -14 3/4°, as opposed to the declination of 210° and inclination of -15 1/2° calculated for the same region on the basis of the mean Permian pole position as determined from samples obtained from stable parts of the European continent. Such deviations are a common feature of material collected from the neighbourhood of the alpine orogenic belt; in this instance the discrepancy is tentatively explained in terms of regional strike-slip faulting

Alternating Field Demagnetazation of Rocks, and the Problemov Geromagnetic Remenance

Alternating field (a.f.) demagnetization has proved to be a very reliable technique for separating the magnetization components of rock samples. The method is subject to errors caused by either imperfection of the technique or by intrinsic properties of a rock. Recently; Stephenson [1,2] introduced the term gyroremanent magnetization (GRM) for a disturbing remanent magnetization that can be acquired by magnetic material during tumbling or stationary a.f. demagnetization. The implications for the routine a.f. demagnetization of anisotropic rock samples seemed to be very serious. Here, however, a method is presented on how to avoid the effect of GRM on results obtained from stationary a.f. demagnetization

PALEOMACNETISM AND THE ALPINE TECTONICS OF EURASIA II THE MAGNETISM OF THE PERMIAN PORPHYRIES NEAR LUGANO (NORTHERN ITALY, SWITZERLAND)’

The magnetic properties of 25 oriented samples of the Permian porphyries from the Lugano district are investigated. After a.c. demagnetization (up to 900 Oe peak value) eleven samples produce a characteristic direction of magnetization, declination (D) = N 143.5OE, inclination (I) = -17O. The other samples show streaking towards the direction of the present-day geomagnetic field; their recent magnetic components are very hard and could not be removed by our a.c. demagnetization procedures. The paleomagnetic pole derived from the Lugano rocks is situated at 41.5?N 119.5OW, and is equally divergent from the other Permian poles from extra-Alpine European rocks as are the ones traced in other parts of the Alps. This divergency is best explained by assuming large-scale tectonic displacement

Paleomagnetism and the Alpine tectonics of Eurasia U the magnetism of the Permian porphyries near Lugano (Northern Italy, Switzerland)

The magnetic properties of 25 oriented samples of the Permian porphyries from the Lugano district are investigated. After a.c. demagnetization (up to 900 Oe peak value) eleven samples produce a characteristic direction of magnetization, declination (D) = N 143.5°E, inclination (I) = −17°. The other samples show streaking towards the direction of the present-day geomagnetic field; their recent magnetic components are very hard and could not be removed by our a.c. demagnetization procedures. The paleomagnetic pole derived from the Lugano rocks is situated at 41.5°N 119.5°W, and is equally divergent from the other Permian poles from extra-Alpine European rocks as are the ones traced in other parts of the Alps. This divergency is best explained by assuming large-scale tectonic displacements of the south Alpine unit before and during the Alpine orogenesis

Paleomagnetism and the Alpine tectonics of Eurasia U the magnetism of the Permian porphyries near Lugano (Northern Italy, Switzerland)

The magnetic properties of 25 oriented samples of the Permian porphyries from the Lugano district are investigated. After a.c. demagnetization (up to 900 Oe peak value) eleven samples produce a characteristic direction of magnetization, declination (D) = N 143.5°E, inclination (I) = −17°. The other samples show streaking towards the direction of the present-day geomagnetic field; their recent magnetic components are very hard and could not be removed by our a.c. demagnetization procedures. The paleomagnetic pole derived from the Lugano rocks is situated at 41.5°N 119.5°W, and is equally divergent from the other Permian poles from extra-Alpine European rocks as are the ones traced in other parts of the Alps. This divergency is best explained by assuming large-scale tectonic displacements of the south Alpine unit before and during the Alpine orogenesis

Palaeomagnetism of Suriname dolerites

Permo-Triassic and Precambrian dolerites have been collected for palaeomagnetic research in Suriname (South America) at 24 sites (280 oriented cores)

Paleomagnetism and ore mineralogy of some basalts of the geirud formation of Late Devonian - early carboniferous age from the Southern Alborz, Iran

Basaltic lavas from the southern Alborz, an area about 40 km northeast of Tehran, Iran, have been paleomagnetically investigated. The lavas are of Late Devonian-Early Carboniferous age, and belong to the basal member of the Geirnd Formation. At 11 sites a total of 80 cores was drilled. Detailed analyses by means of progressive demagnetization of the natural remanent magnetization (NRM) were made both by the application of alternating magnetic fields and by heating. Also, on a number of specimens a study was done both with thin sections and with polished sections. There proved to be general agreement between the properties of the characteristic NRM and the kind of Fe-Ti oxides in the lavas. In the case of specimens containing magnetite only the characteristic NRM was entirely removed at temperatures just below 600°C, or in alternating fields up to 1500/2000 Oe peak value; on the other hand, in specimens containing both magnetite and a substantial part of hematite (martite) the final part of the characteristic remanence was removed at temperatures above 600°C, and this remanence resisted alternating fields above 2000 Oe peak value. From the characteristic site-mean directions of 5 sites an average paleomagnetic direction is computed with D = 210.8 °, 1 = 66.9 °, and c~95 = 3.9 °. This result might be taken as an indication that at the Devono-Carboniferous transition the southern part of the Alborz was located in the present Indian Ocean off the Arabian coast

Late miocene magnetobiostratigraphy of Crete

Six Upper Miocene marine clay sections on Crete (Greece) have been subjected to a detailed magnetobiostratigraphic analysis. Six correlatable polarity zones are recognized and these demonstrate the regional synchrony of planktonic foraminiferal biohorizons. By way of correlation to the magnetic polarity time-scale of Lowrie and Alvarez (1981), the Cretan sequence is assigned to polarity chronozones 5 (anomaly 3A) and 6. The new chronology provides an age of 5.6 Ma for the first occurrence datum (FOD) of the Globorotalia conomiozea group in the Mediterranean, an age of 6.0 Ma for the FOD of G. menardii form 5 and an age of 6.6 Ma for the last occurrence datum (LOD) of G. menardii form 4. Correlating the polarity record of the New Zealand Blind River section (Kennett and Watkins, 1974), with the magnetic polarity time-scale provides an age of 6.0 Ma for the evolutionary appearance of Globorotalia conomiozea, which is in complete agreement with the age of 6.1 ± 0.1 Ma given by Loutit and Kennett (1979). The demonstrated diachrony of 0.4 Ma between the New Zealand FOD of G. conomiozea and its Mediterranean counterpart is explicable in view of the different nature of the two events, the one in New Zealand being evolutionary and the one in the Mediterranean migrational. The FOD of the G. conomiozea group in the*Tortonian/Messinian boundary stratotype section coincides with the level proposed by Colalongo et al. (1979) to mark the base of the Messinian. Since the FOD of the G. conomiozea group in Crete and in Sicily are most probably time-equivalent, the age of the Tortonian/Messinian boundary is fixed at 5.6 Ma. The youngest sediments incorporated in this study extend into the Gilbert chronozone and antedate the main evaporitic phase. Consequently, the Messinian evaporitic body is younger than the base of the Gilbert chronozone, the age of which is fixed at 5.3 Ma. Adopting an age of 5.0 Ma for the Miocene/Pliocene boundary would imply that evaporites and post-evaporitic Lago Mare sediments were deposited in some 300,000 years and suggests that in the central parts of the Mediterranean basins evaporites must have accumulated at rates of some 3 m per 1000 years