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.

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.

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.

Paleomagnetism, structure, and longitudinal correlation of Middle Precambrian dykes from northwestern Ontario and Minnesota

1986 ◽  
Vol 23 (2) ◽  
pp. 142-157 ◽  
Author(s):  
H. C. Halls
Keyword(s):  
Continental Margin ◽  
Pole Position ◽  
Dyke Swarm ◽  
Time Interval ◽  
Northwestern Ontario ◽  
Longitudinal Correlation ◽  
Paleomagnetic Pole ◽  
The Mean ◽  
Dyke Swarms ◽  
Sufficient Proof

A primary magnetization about 2.1 Ga old is well preserved in the Kenora–Kabetogama dyke swarm in Minnesota and Ontario. Its direction, the mean for 12 dykes, incorporating results from 30 paleomagnetic sites, is 115.9°, −55.6°, yielding a paleomagnetic pole position of latitude 42.7°S, longitude 4.2°E (dm = 7.3°, dp = 5.2°).The primary nature of the magnetization can be demonstrated using geochemistry to correlate individual dykes over distances that can exceed 300 km. Whereas the remanence direction varies between dykes, it remains constant along a dyke, sufficient proof that it was formed during initial cooling of the intrusion.A weak, longitudinal increase in hydrous alteration, MgO content, and degree of magnetic overprinting is observed as the swarm is followed to the south and may reflect increasing proximity to a Precambrian continental margin that underwent rifting, sedimentation, and deformation during the time interval 2.2–1.6 Ga BP. Although the cause of the longitudinal changes in terms of margin evolution can only be surmised, the results illustrate the potential of dyke swarms as sensitive indicators of how shield terrains may respond to events occurring around their margins.

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.

Paleomagnetism of some Grenville Province Rocks

1973 ◽  
Vol 10 (8) ◽  
pp. 1175-1190 ◽  
Author(s):  
H. C. Palmer ◽  
C. M. Carmichael
Keyword(s):  
North America ◽  
Remanent Magnetization ◽  
Present Position ◽  
Grenville Province ◽  
Paleomagnetic Pole ◽  
The Pacific

Anorthositic rocks 20 to 30 km south of the Grenville Front in the Grenville Province of Ontario have a stable remanent magnetization which yields a paleomagnetic pole at 161 °E, 8 °N. This pole is close to other poles from the Precambrian of North America of 1050 m.y. age. Paleomagnetic results have also been obtained from two rock units in the southern part of the Grenville Province of Ontario. These are a pyroxenite exposed near Wilberforce and the Tudor Gabbro exposed near Madoc. The directions of remanent magnetization yield pole positions as follows: Wilberforce pyroxenite—148 °E, 14.5 °S; Tudor Gabbro—137 °E, 17 °N. These pole positions, together with others from the literature, which have been derived from rock units 200 km or more south of the Grenville Front, plot farther west in the Pacific than do poles of inferred similar age from other regions of North America. A possible interpretation of these results is that the southern part of the Grenville province was formed some 30° SE of its present position.

Paleomagnetism of the Precambrian Martin Formation, Saskatchewan

1973 ◽  
Vol 10 (10) ◽  
pp. 1485-1493 ◽  
Author(s):  
M. E. Evans ◽  
D. K. Bingham
Keyword(s):  
North America ◽  
Strong Evidence ◽  
Sedimentary Basins ◽  
Canadian Shield ◽  
Igneous Rocks ◽  
Paleomagnetic Pole ◽  
Oriented Samples ◽  
The Subject

Oriented samples of the Martin Formation were collected from 23 sites, both sediments and igneous rocks being represented. Detailed laboratory treatment yields an overall mean direction corresponding to a paleomagnetic pole at 9 °S, 72 °W (dp = 6.3°, dm = 11.5°). Strong evidence for the primary nature of the magnetization involved is provided by a positive fold test. The paleomagnetic pole obtained provides further evidence for a major eastward loop in the polar wandering path for North America during late Aphebian – early Helikian times. The exact age of Martin Formation deposition is the subject of debate, but extreme limits given by various authors are 1930 to 1490 m.y. However, the paleomagnetic results themselves somewhat restrict this range, and are of use in setting up a regional chronology, since they enable stratigraphic correlations between isolated sedimentary basins of the Canadian Shield to be made.

Paleomagnetism of Jurassic Rocks from Southern Alaska, and the Tectonic Implications

1974 ◽  
Vol 11 (7) ◽  
pp. 976-997 ◽  
Author(s):  
D. R. Packer ◽  
D. B. Stone
Keyword(s):  
North America ◽  
Opposite Direction ◽  
Selection Criteria ◽  
Baja California ◽  
Pole Position ◽  
Clockwise Rotation ◽  
Oriented Samples ◽  
Tectonic Development ◽  
Jurassic Rocks ◽  
The Mean

Oriented samples of rocks of Jurassic age were collected from 24 separate sites located in southern and southwestern Alaska. Paleomagnetic measurements were made on these rocks, and various selection criteria were applied to obtain a mean Jurassic paleopole position of 50°N and 295°E with an α95 of 14.2°. This pole position is displaced from the mean paleopole of North America in the opposite direction to that predicted by Carey's orocline hypothesis for the development of Alaska. Based on this pole position, northward movement and clockwise rotation of southern Alaska must have occurred since Jurassic times, perhaps in a manner analogous to the motion of Baja California today. This Baja–Alaska model for the tectonic development of southern Alaska is currently being tested.

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.

Paleomagnetism of the Mesozoic Coast Parallel Dolerite Dikes of West Greenland

1975 ◽  
Vol 12 (7) ◽  
pp. 1244-1248 ◽  
Author(s):  
W. F. Fahrig ◽  
G. Freda
Keyword(s):  
North America ◽  
Pole Position ◽  
West Greenland ◽  
Drill Cores

Paleomagnetic measurements on 61 drill cores from eight sites of the Coast Parallel dikes of west Greenland (Fiskenaesset area) have yielded a pole position at 169°E, 54°N, α95 = 5.9°. When these data are combined with those from the Nunarsuit-Tornarssuk area (Ketelaar 1963) the pole is 168°E, 56°N, α95 = 6°. Reversely magnetized dikes are present in both areas.The Coast Parallel dike pole lies close to the Triassic pole position for North America if corrected for Bullard's fit. The dikes were therefore intruded prior to the Mesozoic separation of Greenland and North America.

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