scholarly journals Upper Devonian (Frasnian stage) of the north-western part of the Russian Platform: paleomagnetic data

2020 ◽  
Vol 15 (4) ◽  
Author(s):  
A.G. Iosifidi ◽  
◽  
V.V. Popov ◽  
A.V. Zhuravlev ◽  
◽  
...  
Keyword(s):  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Upper Devonian ◽  
Paleomagnetic Data ◽  
Magnetic Minerals ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Pole ◽  
Frasnian Stage ◽  
Main Devonian Field

Paleomagnetic determinations for the Devonian strata of the Main Devonian Field, available in the international paleomagnetic data base, do not make it possible to construct both detailed magnetostratigraphic scales and reliable trajectories of the apparent polar wander path of the paleomagnetic pole. This is primarily due to the insufficient amount of data that determine modern reliability criteria. Obtaining more complete series of reliable paleomagnetic determinations is one of the important tasks of paleomagnetic studies. The paper presents new paleomagnetic determinations from a collection of rocks of the Frasnian stage of the Upper Devonian (Ilmen and Bureg Beds of the Semiluky Formation), sampled on the southern shore of Lake Ilmen, east of the village. Korostyn in 2009. Magnetomineralogical studies were carried out to determine the magnetic minerals of carriers of natural remanent magnetization. Three characteristic components of natural remanent magnetization have been identified. Two components correspond to the Late Paleozoic magnetization reversal (in the Carboniferous and Permian times). The third, bipolar component of the Frasnian age passes the reverse polarity test of the geomagnetic field.. The obtained position of the paleomagnetic pole by the bipolar component of the natural remanent magnetization is consistent with the available data on the section of the Late Upper Devonian of the Main Devonian Field.

Paleomagnetism of Archean rocks from northwestern Ontario: Wabigoon gabbro, Wabigoon Subprovince

1983 ◽  
Vol 20 (12) ◽  
pp. 1805-1817 ◽  
Author(s):  
David J. Dunlop
Keyword(s):  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Blocking Temperature ◽  
Virtual Geomagnetic Pole ◽  
Polar Wander ◽  
Apparent Polar Wander Path ◽  
Northwestern Ontario ◽  
Paleomagnetic Pole ◽  
Geomagnetic Pole ◽  
Chemical Remanent Magnetization

The Wabigoon gabbro of the Archean Wabigoon greenstone belt in northwestern Ontario preserves a univectorial natural remanent magnetization (NRM) with D = 246°, I = 12° (k = 19.5, α95 = 10.5°, N = 11 sites). The precision is reduced if sample means are averaged, however (k = 9.3, α95 = 9.2°, N = 29 samples). The paleomagnetic pole falls either at 160°W, 11°S (δp = 5.3°, δm = 10.6°), corresponding to an age of ~1300 Ma on the Laurentian apparent polar wander path, or the reverse of this, 20°E, 11° N, corresponding to a late Archean age (~2800 Ma). No ~1300 Ma igneous or metamorphic event is known in the area; a major west-northwest-trending dike about 9 km south of the gabbro yields a virtual geomagnetic pole at 122°W, 45°N and seems to be of Abitibi age (~2150 Ma) rather than Mackenzie age (~1250 Ma). A few gabbro samples and some greenstones from the intrusive baked zone have hybrid remanences in which a higher blocking temperature Kenoran-age (~2600 Ma) NRM is superimposed on the gabbro characteristic NRM. However, the Kenoran component may be a younger chemical remanent magnetization (CRM) residing in hematite. The hypothesis that the gabbro characteristic remanence is itself a hybrid of Kenoran and Keweenawan (~1100 Ma) NRM's, which would explain both the high between-sample scatter and the lack of a ~1300 Ma remagnetizing event, is considered but rejected because fewer than 10% of the gabbro samples exhibit multivectorial swings during alternating field or thermal cleaning. Two geomagnetic field reversals are recorded at interior sites, but only one or none is recorded near the margin of the intrusion. The different cooling histories of margin and interior, as well as the bulk of the other evidence, favour magnetization during initial cooling in late Archean time.

Magnetic remanence in the Chalk of eastern England: an unusually resistant VRM?

1994 ◽  
Vol 131 (5) ◽  
pp. 593-608 ◽  
Author(s):  
Graham J. Borradaile
Keyword(s):  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Single Component ◽  
Magnetic Minerals ◽  
Magnetic Remanence ◽  
Ferro Magnetic

AbstractA single component, natural remanent magnetization (NRM) is carried largely by pseudosingle domain magnetite in the Cretaceous Lower Chalk and Red Chalk of eastern England. The Red Chalk also records the same direction in haematite. Most of the ferro-magnetic minerals occur as primary clastic or early diagenetic grains. A stable remanence component is resistant to demagnetization, and is carried by both magnetite and haematite. Nevertheless, it has a steep inclination close to the present Earth's field and it is too steep for the previously reported palaeolatitude of these rocks at the time of sedimentation. A postglacial slump breccia scatters the ChRM but also provides some evidence of viscous, partial magnetic overprinting during slumping. Despite its resistance to thermal and alternating field demagnetization the characteristic remanent magnetization (ChRM) is probably a young Bruhnes epoch viscous remanent remagnetization (VRM).

Borden dykes of Baffin Island, Northwest Territories: a Franklin U-Pb baddeleyite age and a paleomagnetic reinterpretation

1999 ◽  
Vol 36 (1) ◽  
pp. 65-73 ◽  
Author(s):  
Sally J Pehrsson ◽  
Kenneth L Buchan
Keyword(s):  
Northwest Territories ◽  
Remanent Magnetization ◽  
Paleomagnetic Data ◽  
Dyke Swarm ◽  
Baffin Island ◽  
Normal Faulting ◽  
Polar Wander ◽  
Baffin Bay ◽  
The North ◽  
Chemical Remanent Magnetization

U-Pb baddeleyite geochronology for two Borden diabase dykes of northern Baffin Island gives an intrusion age of ca. 720 Ma, coeval with the age established elsewhere for the Franklin igneous event. Thus, the Borden dykes belong to the Franklin dyke swarm, rather than forming a separate swarm that intruded at ca. 950-900 Ma, as has been suggested previously on the basis of paleomagnetism and K-Ar ages. As a result, the paleopole from the Borden dykes can no longer be utilized to help constrain the ca. 1050-850 Ma Grenville Loop of the North American polar wander path. Reevaluation of paleomagnetic data for the dykes of northern Baffin Island suggests that Borden dyke magnetizations resulted from superposition of a steeply directed component of chemical remanent magnetization on normal and reversed primary Franklin components. The overprint direction is consistent with a Cretaceous-Tertiary age and is likely related to normal faulting and graben development during the opening of Baffin Bay.

scholarly journals Magnetic Mineralogy of Speleothems From Tropical-Subtropical Sites of South America

2021 ◽  
Vol 9 ◽  
Author(s):  
Plinio Jaqueto ◽  
Ricardo I. F. Trindade ◽  
Joshua M. Feinberg ◽  
Janine Carmo ◽  
Valdir F. Novello ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
South America ◽  
Remanent Magnetization ◽  
Drainage Basin ◽  
Environmental Magnetism ◽  
Rank Correlation ◽  
Natural Remanent Magnetization ◽  
Magnetic Minerals ◽  
Magnetic Mineralogy ◽  
Diverse Range

Fe-bearing minerals are a tiny fraction of the composition of speleothems. They have their origin in the karst system or are transported from the drainage basin into the cave. Recent studies on the magnetism of speleothems focused on the variations of their magnetic mineralogy in specific time intervals and are usually limited to a single sample. In this study, we describe a database of environmental magnetism parameters built from 22 stalagmites from different caves located in Brazil (South America) at different latitudes, comprising different climates and biomes. The magnetic signal observed in these stalagmites is dominated by low-coercivity minerals (∼20 mT) whose magnetic properties resemble those of the magnetite formed in pedogenic environments. Also, a comparison with few samples from soils and the carbonate from cave’s walls shows a good agreement of the magnetic properties of speleothems with those of soil samples, reinforcing previous suggestions that in (sub-)tropical regimes, the dominant magnetic phase in speleothems is associated with the soil above the cave. Spearman’s rank correlation points to a positive strong correlation between magnetic concentration parameters (mass-normalized magnetic susceptibility, natural remanent magnetization, anhysteretic remanent magnetization, and isothermal remanent magnetization). This implies that ultrafine ferrimagnetic minerals are the dominant phase in these (sub-)tropical karst systems, which extend across a diverse range of biomes. Although the samples are concentrated in the savannah biome (Cerrado) (∼70%), comparison with other biomes shows a higher concentration of magnetic minerals in speleothem underlying savannahs and lower concentration in those underlying moist broadleaf forests (Atlantic and Amazon biome) and dry forests (Caatinga). Thus, rainfall, biome, and epikarst dynamics play an important role in the concentration of magnetic minerals in speleothems in (sub-)tropical sites and indicate they can be an important target for paleoenvironmental research in cave systems.

Paleomagnetism of the late Paleozoic Slide Mountain terrane, northern and central British Columbia

1993 ◽  
Vol 30 (9) ◽  
pp. 1898-1913 ◽  
Author(s):  
David R. Richards ◽  
Robert F. Butler ◽  
Tekla A. Harms
Keyword(s):  
British Columbia ◽  
Vertical Axis ◽  
Natural Remanent Magnetization ◽  
Tilt Test ◽  
Lower Permian ◽  
Polar Wander ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Reversed Polarity ◽  
Axis Rotation

Paleomagnetic samples were collected from Mid-Pennsylvanian to Lower Permian red argillaceous cherts at two localities of the Slide Mountain terrane: 18 sites from the Sylvester allochthon in northern British Columbia and 11 sites from Sliding Mountain in central British Columbia. A secondary component of natural remanent magnetization in the Sylvester samples yields a paleomagnetic pole that can be brought into coincidence with the Jurassic portion of the North American apparent polar wander path by inferring vertical-axis rotation during obduction of the allochthon. Both localities yield a characteristic component (ChRM) with unblocking temperatures from 650 to 680 °C. After structural correction for bedding tilt, all inclinations of ChRM are negative, consistent with magnetization during a reversed-polarity interval in the northern hemisphere. Site-mean ChRM directions show consistent inclinations but distinct stratigraphic groupings of declinations. Inclination-only statistics indicate that the ChRM passes a tilt test within the Sylvester allochthon and regionally between the two localities. The ChRM was apparently acquired prior to structural imbrication within the Sylvester section and regional differential tilting. We interpret the ChRM to be a primary magnetization acquired at or soon after deposition during the Permo-Carboniferous reversed-polarity superchron. The mean ChRM inclination of −16.7° ± 6.0° from the Sylvester allochthon indicates a paleo-latitude of 8.8° ± 3.4°N, which is corroborated by a paleolatitude of 1.9° ± 1.5°N from the Sliding Mountain locality. When compared with expected Pennsylvanian–Permian paleolatitudes, a net poleward translation of 20.3 ± 3.7° is implied for at least the sampled lithotectonic component of the Sylvester allochthon.

New paleomagnetic results obtained in Upper Cretaceous-Paleocene detritic deposits of the North Iberian Meseta

2021 ◽  
Author(s):  
Juan José Villalaín ◽  
Pablo Calvín ◽  
Puy Ayarza ◽  
Ruth Soto ◽  
Manuel Calvo
Keyword(s):  
Upper Cretaceous ◽  
Magnetic Anomalies ◽  
Ocean Floor ◽  
Paleomagnetic Data ◽  
Necessary Condition ◽  
Western Tethys ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Kinematic Evolution ◽  
Paleomagnetic Poles

<p>The Iberian microplate and its evolution during the Mesozoic have been in-vogue topics in the field of Geodynamics, because of its location between two of the major tectonic plates, its interaction with both of them, and its significance in relation with the evolution of the western Tethys domain. Geodynamic models of Mesozoic Iberian evolution are based upon the knowledge of the kinematics of the microplate obtained from the ocean floor magnetic anomalies and particularly its apparent polar wander path (APWP) defined by existing paleomagnetic data. In this sense, the most important feature is the anticlockwise 30º-40º rotation that Iberia underwent during the Cretaceous. Nevertheless, there are still uncertainties about the chronology of this movement due to the poor definition of oceanic magnetic anomalies and the scarcity of high-quality paleomagnetic data in the continent. According to recent works, existing paleomagnetic poles are contradictory and inconsistent with the global apparent wander path (GAPWP) and ocean floor anomalies. This is due to the widespread presence of remagnetizations in the Mesozoic basins within Iberia.</p><p>To address this question we are starting to develop a new project that aims to obtain new paleomagnetic data from unexplored geological units meeting the necessary condition to obtain new Cretaceous paleomagnetic poles representative of the Iberian plate. In this talk we show new paleomagnetic data from detritic deposits with siliceous cement located at the Duero basin (North Iberian Meseta) ascribed to the upper Cretaceous-Paleocene (Areniscas de Salamanca Formation). A stable paleomagnetic component carried by hematite, showing normal and reversed polarities has been isolated. A stable paleomagnetic component carried by hematite, showing normal and reversed polarities has been isolated. We discuss the primary character of this magnetization in terms of inferring the age of this unit in the frame of the kinematic evolution of the plate.  </p>

scholarly journals Remagnetization of Permian Emeishan basalts: Constraints on the timing of native copper mineralization in northeast Yunnan Province, China

2021 ◽  
Vol 8 ◽  
Author(s):  
Chengying Liu ◽  
Greig A. Paterson ◽  
Shihu Li ◽  
Yongxin Pan ◽  
Rixiang Zhu
Keyword(s):  
South China ◽  
Middle Jurassic ◽  
Remanent Magnetization ◽  
Yunnan Province ◽  
Natural Remanent Magnetization ◽  
South China Block ◽  
Native Copper ◽  
Copper Mineralization ◽  
Paleomagnetic Pole ◽  
Normal Polarity

New paleomagnetic results from the Permian Emeishan basalts in the Zhaotong area, NE Yunnan province, China show four natural remanent magnetization components. Detailed stepwise thermal demagnetization of basaltic samples from 16 flows from the Dadi section, which represent basalt units III and IV, isolated two groups of characteristic remanent magnetizations. Samples in unit IV (five flows) record a southwest declination and a moderate downward inclination that is considered to be a partial remagnetized remanence. The bottom flows from unit III (11 flows) record a normal polarity direction, interpreted as a remagnetization, which yields a tilt-corrected mean direction of Ds/Is = 8.8°/31.6° (N = 9, ks = 39.7, α95 = 8.3°), with a corresponding paleomagnetic pole at 77.1°N, 240.0°E (K = 49.2, A95 = 7.4°). The secondary directions have steeper inclinations than primary ones that have been successfully recovered from other studies in this area of the Emeishan basalts. By comparison with the Phanerozoic paleomagnetic poles of the South China Block, the preferred timing of remagnetization is the Lower-Middle Jurassic. Field relationships suggest that the remagnetization of the Emeishan basalts is coeval with the spatially related, but localized, copper mineralization. Thus the timing of the main copper mineralization hosted in the Emeishan basalts is hypothesized to occur in the Early-Middle Jurassic.

Under pressure: How pressure affects magnetic remanence

2020 ◽  
Author(s):  
Michael Volk ◽  
Roger Fu ◽  
Josh Feinberg
Keyword(s):  
Magnetic Field ◽  
Spatial Resolution ◽  
Remanent Magnetization ◽  
Imaging Techniques ◽  
Magnetic Domain ◽  
Natural Remanent Magnetization ◽  
Magnetic Minerals ◽  
Magnetic Imaging ◽  
Magnetic Remanence ◽  
Series Of Experiments

<p>Rocks have complicated histories and form under various conditions. However, all rocks, terrestrial and extraterrestrial, have been subjected to some form of pressure during their genesis. The effect of pressure (strain) on the magnetic remanence is a largely unexplored problem, with most of the work being focused on the study of meteorites. </p><p>In the absence of a magnetic field, subjecting a rock to pressure can demagnetize the natural remanent magnetization (NRM). This loss of magnetic remanence can lead to an underestimation of paleointensities. On the other hand, in the presence of a magnetic field, magnetic minerals can record a pressure remanent magnetization (PRM). The superposition of the remaining NRM and a newly acquired PRM can influence the remanence direction as well as the paleointensity. Since the reconstruction of the temporal changes of Earths’ magnetic relies on robust estimations of direction and intensity, the effects of pressure on the remanence should be taken into account.</p><p>Here we present a series of experiments that aim to explore the acquisition process of PRMs and their net contribution with respect to the rock’s original magnetization. Stoichiometric magnetites of four different grain sizes (65 nm, 440 nm, 16.9 µm, and 18.3 µm) and magnetic domain states were subjected to crustal pressures (226, 301, and 376 MPa) in the presence of a magnetic field. Surprisingly, the PRM intensity showed no detectable dependence on grain size. However, because the acquisition of a thermal remanence (TRM) is strongly dependent on particle size,  populations of large multidomain particles can acquire a PRM, which may represent up to 30% of a TRM acquired in the same field.</p><p>Finally, we will show how the influence of pressure on the magnetic remanence can be visualized by modern magnetic imaging techniques like the quantum diamond microscope (QDM). The QDM has a  ~1 µm maximum spatial resolution that is able to resolve the magnetic fields of individual mineral assemblages with ~10 µm diameter. The high spatial resolution and sensitivity enables us to visualize the changes in magnetic remanence due to pressure cycling and can help to better understand the possible implications for paleomagnetism.</p>

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