PALEOMAGNETISM OF THE ALLARD LAKE ANORTHOSITE SUITE

1967 ◽  
Vol 4 (3) ◽  
pp. 357-369 ◽  
Author(s):  
R. B. Hargraves ◽  
D. M. Burt
Keyword(s):  
Magnetic Field ◽  
Lake Area ◽  
Magnetic Vector ◽  
Soft Magnetic ◽  
Hard Component ◽  
Polar Wander ◽  
Rock Types ◽  
Normal Polarity ◽  
Rock Suite ◽  
Structural Blocks

Analysis of paleomagnetic data on 112 samples of Precambrian anorthosite, norite, pyroxene–syenite and hemo-ilmenite ore from four main localities in the Allard Lake area reveals: (1) A relatively soft magnetic component resides in magnetite, which is of variable abundance in all rock types. The magnetite remanent magnetic vector is of normal polarity, and is more or less directly opposed to a hard component residing in hemo-ilmenite, the predominant oxide. Self-reversal of the permanent magnetism in the hemo-ilmenite is the favored explanation. (2) Disregarding polarity, the stable remanent magnetic vector has similar orientation in all rock types from all four localities (N = 4, α95 = 18.0). This precludes significant differential rotation of individual structural blocks since the rocks became magnetized. Furthermore, either no polar wander occurred during the emplacement and cooling of the entire igneous rock suite, or all these rock types acquired their magnetism simultaneously during subsequent metamorphism. (3) On the centered-axial-dipole model for the earth's magnetic field, the remanent vector in the Allard Lake rocks gives a pole southeast of New-foundland, at coordinates 38°36′ N., 39°36′ W. (α95 = 18.0).

Paleomagnetism of Archean rocks from northwestern Ontario: V. Poohbah Lake alkaline complex, Quetico Subprovince

1985 ◽  
Vol 22 (1) ◽  
pp. 27-38 ◽  
Author(s):  
David J. Dunlop
Keyword(s):  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Reverse Polarity ◽  
Alkaline Complex ◽  
Field Reversal ◽  
Polar Wander ◽  
Fine Grained ◽  
Rock Types ◽  
Northwestern Ontario ◽  
Normal Polarity

The Poohbah Lake alkaline complex is a late synkinematic Kenoran pluton in the Quetico gneiss belt of the western Superior Province. Three units of the complex, porphyritic syenite (PS), malignite (M: a nepheline–clinopyroxene–K-feldspar rock), and hornblende syenite (HS), as well as baked Archean schists near the intrusive contact, have a predominantly reverse-polarity R magnetization with mean direction D = 198° I = −22.5° (k = 62, α95 = 5°, N = 13 sites) and a paleopole at 60°E, 50.5°N. Pyrrhotite and coarse primary magnetite are carriers of the R remanence. PS, M, and biotite pyroxenite (BP) exhibit also a predominantly normal N magnetization carried by fine-grained, probably secondary magnetite. N is systematically steeper than R: its mean direction is D = 359.5° I = +55.5° (k = 28, α95 = 8°, N = 13 sites) with a paleopole at 90°E, 77.5°N. R and N do not record an asymmetric field reversal, since reverse-polarity N vectors and normal-polarity R vectors are occasionally found. R resembles in polarity and direction the natural remanent magnetization (NRM) of the 2630 Ma Matachewan diabase. It is probably the primary NRM of the Poohbah Lake pluton, with an age of about 2650 Ma in approximate agreement with the K/Ar isochron age of 2700 ± 25 Ma. N resembles in polarity and direction NRM's from the 2580 Ma Shelley Lake granite and the late Archean Burchell Lake granite. It is probably a secondary NRM about 2550 Ma in age, as suggested by updated K/Ar mica ages. The characteristic NRM of HS samples and secondary magnetizations in other rock types have poles on the Grenville Track of the polar wander path but there is no evidence for Grenvillian-age events in the area.

scholarly journals On the through-process texture evolution assessment in grain oriented Fe-3 wt% Si steel produced by a novel directional inoculation technique

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Snehashish Tripathy ◽  
Sandip Ghosh Chowdhury
Keyword(s):  
Magnetic Field ◽  
Hot Rolling ◽  
Texture Evolution ◽  
Lattice Parameter ◽  
Soft Magnetic ◽  
Oriented Growth ◽  
Inoculation Technique ◽  
Hot Band ◽  
Ebsd Technique ◽  
Cast Microstructure

AbstractA novel directional inoculation technique has been designed to cast thin slab ingots containing Goss (or near Goss) oriented components in the as cast microstructure under the combined effect of oriented nucleation and oriented growth. The same has been targeted so as to retain Goss orientations and simultaneously develop γ fiber components (ranging from {111}<$$1\overline{1}0$$ 1 1 ¯ 0 > to {111}<112>) during hot rolling. The designed scheme of directional inoculation achieved oriented nucleation by the effect of exogenously added soft magnetic inoculants under magnetic field and oriented growth by the effect of fast cooling rates prevailing in the mould. The choice of 65Fe–35Co (wt%) system as soft magnetic inoculants was made taking into account the similarity in crystal structure and lattice parameter. The chemically synthesized inoculants under the effect of external magnetic field during solidification were able to exhibit directional inoculation. Variation in the cast microstructure and microtexture by varying the extent of inoculant addition was studied by EBSD technique. The ingots cast under different conditions were subjected to a designed hot rolling schedule and the through process microstructural and microtextural evolution was assessed. It was observed that fine equiaxed grains with initial cube orientations in the as cast structure could lead to the most desirable microstructural as well as microtextural gradient in the hot band.

Soft Magnetic Films and Wires for Magnetic Field Sensors

2008 ◽  
pp. 1708-1741
Author(s):  
A. S. Antonov ◽  
I. T. Iakubov ◽  
A. N. Lagarkov ◽  
A. L. Rakhmanov ◽  
I. A. Ryjikov
Keyword(s):  
Magnetic Field ◽  
Magnetic Films ◽  
Soft Magnetic ◽  
Magnetic Field Sensors ◽  
Soft Magnetic Films

Synthesis of palaeomagnetic datasets suggests that the geomagnetic field was persistently non-uniformitarian in the Devonian

2021 ◽  
Author(s):  
Annique van der Boon ◽  
Andy Biggin ◽  
Daniele Thallner ◽  
Mark Hounslow ◽  
Jerzy Nawrocki ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Weak Field ◽  
Paleomagnetic Data ◽  
Independent Evidence ◽  
Tectonic Plates ◽  
Polar Wander ◽  
Push Forward ◽  
Geomagnetic Polarity ◽  
Life On Earth ◽  
Geomagnetic Polarity Time Scale

&lt;p&gt;The Devonian has long been a problematic era for paleomagnetism. Devonian data are generally difficult to interpret and have complex partial or full overprints. These problems arise from paleomagnetic data obtained from both sedimentary and igneous rocks. As a result, the reconstruction of motions of tectonic plates is often troubling, as these rely on apparent polar wander paths constructed from Devonian paleomagnetic poles. Also the geomagnetic polarity time scale for this time period is poorly constrained. Paleointensity studies suggest that the field was much weaker than the field of today, and it has been hypothesised that this was accompanied by many polarity reversals (a hyperreversing field). We review studies on Devonian paleopoles, magnetostratigraphy and paleointensity. We tentatively suggest that the field during the Devonian might have been so weak and perhaps of a non-dipolar configuration, that obtaining reliable paleomagnetic data from Devonian rocks is extremely difficult. &amp;#160;In order to push forward the understanding of the Devonian field, we emphasise the need for studies to provide fully accessible data down to specimen level demagnetisation diagrams. Incorporating all data, no matter how complex or bad they might seem, is the only way to advance the understanding of the Devonian magnetic field. Recent paleointensity studies appear to suggest that the Devonian and Ediacaran were both extreme weak field intervals. For the Ediacaran, it has been hypothesised that the field had an impact on life on earth. A fundamentally weak and perhaps non-dipolar field during the Devonian might have had an influence on evolution and extinctions. As there is a large number of biological crises in the Devonian, we here pose the question whether the Earth&amp;#8217;s magnetic field was a contributing factor to these crises. New independent evidence from the Devonian-Carboniferous boundary suggests that the Hangenberg event was caused by increased UV-B radiation, which is in line with a weak magnetic field.&lt;/p&gt;

Residual total magnetic field, aeromagnetic survey of the Duggan Lake area, part of NTS 76-A/N, Nunavut

2013 ◽  
Author(s):  
F Kiss ◽  
R Dumont ◽  
A Jones
Keyword(s):  
Magnetic Field ◽  
Lake Area ◽  
Aeromagnetic Survey ◽  
Total Magnetic Field
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