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Magnetic properties of Triassic rocks of Svalbard Archipelago: preliminary results

Dudzisz K., Szaniawski R., Michalski K., Krajewski K.

Geology, Geophysics and Environment

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2015

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Vol. 41, no. 1

68

EN

Studies were carried out in three rock formations: the Vardebukta Formation (Early Triassic) and the Bravaisberget Formation (Middle Triassic) from Spitsbergen and the Botneheia Formation (Middle Triassic) from Edgeøya (Eastern Svalbard). Collected samples are diversified and represent various lithologies with different thermal and tectonic histories. Magnetic properties of the specimens were studied using rock-magnetic methods including: thermal demagnetization of saturated isothermal remanent magnetization (SIRM), hysteresis loops and analysis of magnetic susceptibility variations at high temperatures. Subsequently anisotropy of magnetic susceptibility (AMS) and analysis of the structure of natural remanent magnetization (NRM) using thermal and alternating field (AF) demagnetization were investigated. The obtained results show that magnetite represents the main magnetic mineral in all studied rocks, whereas pyrrothite, as a second magnetic information carrier, was noted in some of specimens only. The samples from Edgeøya possess the highest magnetic susceptibility (ca. 240∙10−6 SI) which tends to decrease in sites located further to the west and reaches the minimum value for samples from western Spitsbergen (ca. 30–40∙10−6 SI). AMS studies revealed that the Middle Triassic samples are characterized by inverse magnetic fabric and prolate AMS ellipsoids, whereas the Early Triassic specimens represent normal sedimentary fabric and oblate AMS ellipsoids. Inverse magnetic fabric can be carried by many minerals including: tourmaline, cordierite or goethite (Chadima et al., 2006). For investigated samples two models proposed by Rochette (1988) are highly probable: (1) presence of single-domain elongated magnetite grains or (2) presence of ferroan carbonates whose maximum susceptibility is parallel to the c-axis. Paleomagnetic results of the Botneheia Formation revealed only one characteristic NRM component characterized by steep inclination and maximal unblocking temperatures in range of 425–450°C. In turn, the Early Triassic rocks record several NRM components with partially overlapping unblocking temperatures. We have concluded that different magnetic properties observed in studied rocks might be related to various lithologies but also to distinct tectonic and thermal histories associated with complex tectonic evolution of the Barents Sea Shelf.

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Palaeomagnetic age constraints on folding and faulting events in Devonian carbonates of the Kielce Fold Zone (southern Holy Cross Mountains, Central Poland)

Szaniawski R., Konon A., Grabowski J., Schnabl P.

Geological Quarterly

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2011

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Vol. 55, No. 3

223-234

EN

The results of numerous palaeomagnetic studies performed in the last three decades in Devonian carbonates of the Holy Cross Mountains (HCM) have documented the occurrence of several episodes of remagnetisation. This knowledge was applied in this study to determine the temporal relationships between the acquisition of particular secondary palaeomagnetic components and the formation of tectonic structures. This made it possible to estimate the timing of several episodes in the multistage tectonic evolution of particular folds and faults. We show that the westernmost part of the southern HCM was rotated clockwise after the early Permian. Detailed palaeomagnetic analysis documented also shape modifications in some map-scale and minor folds. This tectonic overprinting of originally Carboniferous folds postdated the early Permian. It was furthermore shown that the N-S trending dextral strike-slip faults studied were active between the early Permian and the Permo/Triassic. Our recent data show also the post-early Permian age of breccia that covers the deformed Devonian strata.

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Model deformacji strefy krawędziowej centralno-wschodniej mikropłyty irańskiej w warunkach konwergencji płyt litosfery —na podstawie badań geologiczno-geofizycznych i modelowań numerycznych

Konon A., Barski M., Koprianiuk M., Nadimi A., Słaby E., Szaniawski R., Wysocka A.

Przegląd Geologiczny

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2010

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Vol. 58, nr 1

42-45

4

Palaeomagnetic age constraints indicate post-Varis can orgin of massive breccia in Wietrznia Quarry (Holy Cross Mountains, Central Poland)

Szaniawski R., Lewandowski M.

Geological Quarterly

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2009

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Vol. 53, No 3

357-362

EN

Palaeomagnetic study has been carried out to resolve the controversy over the age and origin of the massive breccia body exposed in Wietrznia Quarry in the Holy Cross Mountains. The breccia studied consists of variously sized angular fragments of Frasnian and Fammenian limestone and shale infilling a palaeodepression within Frasnian limestone. Forthis purpose, the conglomerate test has been applied that enables determination of the relative age of remanence components and formation of the breccia. Palaeomagnetic analysis of breccia clasts reveals the presence of two characteristic components of magnetization. The observed components are akin to those previously described from in situ rocks at Wietrznia Quarry and from other Devonian carbonates from the Holy Cross Mountains. Such components have been interpreted as early synfolding and postfolding over prints of Viséan and Early Permian age. The palaeomagnetic conglomerate test performed in this study are positive results, indicating that the breccia postdates both components. This implies that the breccia is not of synsedimentary character and postdates Variscan de formation.

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Synthrusting remagnetization of the Krizna nappe: high resolution palaeo- and rock magnetic study in the Strazovce section, Strazovske vrchy Mts, Central West Carpathians (Slovakia)

Grabowski J., Michalik J., Szaniawski R., Grotek I.

Acta Geologica Polonica

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2009

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Vol. 59, no. 2

137-155

EN

Palaeomagnetic studies of the uppermost Jurassic to lower Cretaceous pelagic carbonates in the Krizna nappe in the Strazovske vrchy Mts (Central West Carpathians, Slovakia) revealed the presence of secondary magnetite-related magnetization of exclusively normal polarity (component B), which was most probably acquired during the thrusting episode in the late Cretaceous. Three formations exposed in the Strazovce section were the subject of investigation: Jasenina Kimmeridgian.Tithonian), Osnica (Lower.Middle Berriasian) and Mraznica (Upper Berriasian.Hauterivian). Component B is ubiquitous throughout the section but is strongest in the Mraznica Formation. This formation contains a lot of superparamagnetic particles and shows rock magnetic characteristics typical of chemically remagnetized carbonates. The remaining two formations, although also remagnetized, bear traces of an older, probably primary magnetization (component C). The fold test for component B is apparently positive; however the inclination in pre-folding coordinates is too steep for any expected palaeoinclination of Jurassic to recent age. Additional tectonic correction must be applied to match the palaeoinclinations with expected values. Although there is some uncertainty in this additional correction, all plausible options suggest that the rocks must have been magnetized when they dipped in the opposite direction to the thrusting direction. This interpretation is concordant with the internal tectonics of the Krizna nappe, consisting of imbricated units of duplex-type structure.

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Late Paleozoic geodynamics of the Małopolska Massif in the light of new paleomagnetic data for the southern Holy Cross Mountains

Szaniawski R.

Acta Geologica Polonica

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2008

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Vol. 58, no. 1

1-12

EN

Paleomagnetic studies of Devonian carbonate rocks in the southern Holy Cross Mountains have been conducted, the general aim being to verify the occurrence of hypothetical pre-Variscan rotations of the Małopolska Massif as well as to examine time-relationships between remagnetizations and successive stages in tectonic deformations. The paleomagnetic analysis confirms the presence of the three components of characteristic remnant magnetization. Two magnetite-bearing components display reversed (component A) and normal (component B) polarity. The third component (C) is recorded on hematite and shows reversed polarity. Component B is of synfolding origin and has been recorded during the Visean, whereas components A and C are of postfolding origin and represent Early Permian and Permo-Triassic overprints. These results confirm the stable position of the Małopolska Massif with respect to the East European craton, at least since the Visean. Results of fold tests imply that the earliest phases of Variscan deformation can be dated most probably as Visean, while formation of the main Variscan fold structures was completed during the Early Permian. It is also documented that representative Variscan folds did not significantly change their geometry during Maastrichtian-Paleocene reactivation.