The paleomagnetism of the Michikamau anorthositic intrusion, Labrador

1968 ◽  
Vol 5 (5) ◽  
pp. 1139-1144 ◽  
Author(s):  
G. S. Murthy ◽  
W. F. Fahrig ◽  
D. L. Jones
Keyword(s):  
Magnetic Field ◽  
North America ◽  
Pole Position ◽  
Alternating Magnetic Field ◽  
Paleomagnetic Pole ◽  
The Stability

Twenty-nine oriented cores have been collected from six sites in the Michikamau Intrusion in Labrador. This had previously been well dated at 1400 m.y. by the potassium–argon method. A fold test has been applied to the paleomagnetic results after alternating magnetic field demagnetization. The results suggest that the magnetization was acquired with the rocks in their present attitudes. The stability of the magnetization has been well tested and it is concluded that the observed magnetization is thermo-remanent and represents the direction of the earth's field at the intrusion at the time of its formation. The paleomagnetic pole position for the intrusion lies at 0.5° S, 144.7° W, with A95 = 5.6°. It is difficult to compare this result with most other Precambrian results from North America due to uncertainties in age equivalences. However, a comparison with recently published results from well-dated rocks from Colorado–Wyoming suggests there have been no large relative movements between this region and Labrador for the last 1400 million years.

Extent of Grenvillian remanence components in rocks of the Southern Province

1982 ◽  
Vol 19 (4) ◽  
pp. 698-708 ◽  
Author(s):  
M. Stupavsky ◽  
D. T. A. Symons
Keyword(s):  
Magnetic Field ◽  
North America ◽  
Thin Section ◽  
Sedimentary Rocks ◽  
Pole Position ◽  
River Valley ◽  
Field Reversal ◽  
Paleomagnetic Study ◽  
Northern Portion ◽  
Sediment Matrix

Early Aphebian Gowganda sedimentary rocks and intruding Nipissing diabase sills were sampled for paleomagnetic study at 88 sites (~500 cores, ~1000 specimens) along two ~42 km long profiles extending north from the Grenville Front into the Cobalt Plate of the Southern Structural Province in the River Valley – Lake Temagami area of Ontario. After AF demagnetization a postfolding pre-Nipissing ~2200 Ma remanence was found in eight of the 37 Gowganda sediment sites that were > 2 km north of the front, giving a pole at 109°W, 63°N (dp = 10°, dm = 19°). The Nippissing diabase from > 2 km north of the front retains a stable antiparallel prefolding N1 remanence direction in 22 of 40 sites, giving a pole position of 85°W, 17°S (dp = 6°, dm = 10°). These "south and down" remanence directions found in the southern portion of the plate contrast with the antiparallel "north and up" directions found in the northern portion, thereby indicating the occurrence of either two nearly cogenetic Nipissing intrusive events or the sequential emplacement of the Nipissing during an Earth's magnetic field reversal across the plate. At two sites a Nipissing remagnetized remanence was found in Gowganda sediments with a pole of 115°W, 18°S. Also three "Nipissing" sites give a pole at 164°W, 3°N, which is close to the known pole for the later ~1.25 Ga Sudbury olivine diabase dikes. One site is adjacent to a large dike and two were found on thin-section examination to be olivine diabase. The eight sites in Gowganda sediment matrix and conglomerate clasts and in Nipissing diabase from within < 2 km from the front were found to have a postfolding metamorphic remanence with a Grenville orogenic pole at 45°W, 51°N (dp = 19°, dm = 21°). Finally, the results lead to a suggested revision in the APW path for the ~2300–~1650 Ma interval for North America.

Paleomagnetism of igneous rocks from the Belcher Islands, Northwest Territories, Canada

1980 ◽  
Vol 17 (7) ◽  
pp. 807-822 ◽  
Author(s):  
P. W. Schmidt
Keyword(s):  
North America ◽  
Northwest Territories ◽  
Igneous Rock ◽  
Pole Position ◽  
Igneous Rocks ◽  
Hudson Bay ◽  
Plate Model ◽  
Polar Wander ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Pole

Paleomagnetic results from igneous rock units on the Belcher Islands, Hudson Bay, are described. Fold tests for all units studied, as well as a contact test for the intrusive bodies, indicate that both primary (initial), and secondary (post-folding) magnetizations are present.The paleomagnetic pole position from primary directions of the oldest unit studied, the Eskimo volcanics, is situated at 40°S, 002°E (A95 = 12°) and is similar to that derived from equivalent volcanics on the mainland. The younger volcanic unit studied, the Flaherty volcanics, yielded a pole position from primary directions at 0°, 244°E (A95 = 7°). The Haig intrusions, associated with these younger volcanics, yields an almost identical pole position at 1°N, 247°E (A95 = 6°), being derived from directions which are shown to be not only pre–folding but also date from initial cooling. The Eskimo volcanics, which have been more deeply buried than the Flaherty (upper) volcanics, carry substantial components of secondary (post-folding) magnetization which yield a pole position at 19°N, 243°E (A95 = 15°), about 20° north of the pole positions derived from the youngest units.It is argued that the apparent polar wander path (APWP) constructed for the Belcher Islands is representative of the mainland Ungava Craton. Comparison with the equivalent APWP from elsewhere in North America shows that the two APWP's are at variance. Although a two-plate model could be advanced, perhaps a more conservative interpretation is to extend the existing North American APWP eastward to include the Belcher–Ungava APWP, that is, to favour a one-plate model.

The petrology, geochemistry, and remanent magnetization of metabasalts and metagabbros in the Lac Patu – Fort McKenzie region, New Quebec Territory

1976 ◽  
Vol 13 (6) ◽  
pp. 838-846 ◽  
Author(s):  
Maurice K.-Seguin
Keyword(s):  
Remanent Magnetization ◽  
Pole Position ◽  
Magnetic Memory ◽  
Paleomagnetic Pole ◽  
Lower Proterozoic ◽  
Pertinent Information ◽  
The Mean ◽  
The Stability ◽  
Anhysteretic Magnetization ◽  
Chemical Description

One hundred and five specimens were collected from 40 different sites in northwest-striking metabasalts and metagabbros of Lower Proterozoic (Aphebian) age in the northeastern part of the Labrador Trough (longitude: 69 °W, latitude: 57 °N). The radiogenic age determinations of surrounding rocks of the same age yielded 1860 m.y. A petrological and chemical description of the rocks is included. The chemical results for total Fe, MgO, and Na2O + K2O combined, drawn on a ternary diagram show that the metabasalts and metagabbros fall in the tholeiite field. Magnetite (with some occasional 5% ulvospinel) is the most frequent magnetic memory carrier; pyrrhotite is less commonly found. In order to obtain some pertinent information relative to the stability of the NRM component, step-wise alternating field demagnetization was conducted on 40% of the specimens and the others were demagnetized at a specific AF intensity. In 35% of the specimens, the AF demagnetization process induced an anhysteretic magnetization component above 250 Oe. A secondary isothermal remanent magnetization of lesser stability was often detected in the 50–150 Oe range. Tilting of the formations sometimes increased and sometimes decreased the dispersion of the NRM vectors. After tilting the lithological units that were AF demagnetized, the mean paleomagnetic pole position is 152 °E, 20° S (dm = 14°,dp = 07°, K = 34), with at least one reversal.

scholarly journals Instability of a plane conducting free surface submitted to an alternating magnetic field

1998 ◽  
Vol 375 ◽  
pp. 65-83 ◽  
Author(s):  
Y. FAUTRELLE ◽  
A. D. SNEYD
Keyword(s):  
Magnetic Field ◽  
Free Surface ◽  
Growth Rates ◽  
Critical Magnetic Field ◽  
Hill Equation ◽  
Alternating Magnetic Field ◽  
Time Averaging ◽  
Weak Formulation ◽  
Field Frequency ◽  
The Stability

This paper considers the stability of a horizontal liquid-metal free surface in the presence of a horizontal alternating magnetic field. A weak formulation is used to derive a generalized Mathieu–Hill equation for the evolution of surface perturbations. Previous studies which rely on time-averaging the electromagnetic force over one field cycle have predicted a generally weak instability, but we find much larger growth rates near the resonances, where the surface wave frequency is an integral multiple of the field frequency. The method can be extended to include viscous and ohmic damping; the former has little effect, while the latter damps all waves except those whose frequency is close to the field frequency. Growth rates can be closely approximated by simple algebraic formulae, as can the critical magnetic field strength for the onset of instability.

The effect of an alternating magnetic field on the stability of hard levitation of high-temperature superconductors

1998 ◽  
Vol 53 (1-2) ◽  
pp. 177-181 ◽  
Author(s):  
B.M. Smolyak ◽  
M.V. Babanov ◽  
G.V. Ermakov ◽  
E.V. Postrekhin ◽  
L.W. Shou ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
High Temperature Superconductors ◽  
Alternating Magnetic Field ◽  
The Stability

Paleomagnetism of the Michael Gabbro and Possible Evidence of the Rotation of Makkovik Subprovince

1972 ◽  
Vol 9 (10) ◽  
pp. 1287-1296 ◽  
Author(s):  
W. F. Fahrig ◽  
A. Larochelle
Keyword(s):  
North America ◽  
Remanent Magnetization ◽  
Pole Position ◽  
Canadian Shield ◽  
Main Body ◽  
Central Coast ◽  
Tectonic Event ◽  
South Central ◽  
Paleomagnetic Pole ◽  
Paleomagnetic Study

The Michael gabbro forms a belt of thick, predominantly southerly-dipping sheets which extends 200 km inland from the south-central coast of Labrador. The intrusions lie largely within the Makkovik subprovince, have a radioisotopic age of 1500 m.y., and are reversely magnetized with a paleomagnetic pole position of 163 °E, 10 °N. The paleomagnetic results indicate that most of the rocks internal to this belt have not been deformed since the intrusions acquired a stable remanent magnetization, presumably at the time of cooling 1500 m.y. ago. However, the Michael pole position differs significantly from those of rocks of similar age elsewhere in North America. This suggests rotation of the block containing the Michael intrusions relative to these other rocks. The Aillik dikes which also lie within the Makkovik sub-province have a radioisotopic age of about 1100 m.y. and a pole position consistent with that of rocks of similar age elsewhere in the Canadian Shield. The postulated Michael rotation must then have taken place between 1500 and 1100 m.y. ago.The rock at two of the most southerly sites sampled for paleomagnetic study proved to be magnetically unstable and the rock at a third such site, though stably magnetized has a magnetization significantly different from the main body of Michael gabbro intrusions. These three sites may indicate a post-consolidation thermal and tectonic event and their position may help define the Grenville Front in this region.

The paleomagnetism of the Croker Island Complex, Ontario, Canada

1969 ◽  
Vol 6 (2) ◽  
pp. 213-218 ◽  
Author(s):  
H. C. Palmer
Keyword(s):  
North America ◽  
Remanent Magnetization ◽  
Pole Position ◽  
Lake Huron ◽  
Time Interval ◽  
Significant Shift ◽  
Paleomagnetic Pole ◽  
Oriented Samples

Meaningful paleomagnetic results were obtained from 23 of 30 oriented samples from the Croker Island Complex, North Channel of Lake Huron, Canada. The age of the complex is estimated to be 1475 ± 50 m.y. from a Rb–Sr isochron. The paleomagnetic pole calculated from the directions of remanent magnetization after partial ac demagnetization is 143 °West, [Formula: see text] North. This result, when compared with other paleomagnetic results from North America, indicates little or no polar wandering in the time interval 1.48 b.y. to 1.1 b.y. However, a significant shift in the pole position is indicated during the time interval 1.7 to 1.48 b.y.

EXPERIMENTAL STUDY OF THE STABILITY OF NbTi COMPOSITE CONDUCTOR UNDER THE INFLUENCE OF PULSED MAGNETIC FIELD

1984 ◽  
Vol 45 (C1) ◽  
pp. C1-495-C1-498
Author(s):  
Yi Changlian ◽  
Chang Hung ◽  
Yan Luguang ◽  
Chen Jinlin
Keyword(s):  
Magnetic Field ◽  
Experimental Study ◽  
Pulsed Magnetic Field ◽  
The Stability ◽  
Composite Conductor
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