Paleomagnetic evidence for the extent of Mackenzie igneous events

1969 ◽  
Vol 6 (4) ◽  
pp. 679-688 ◽  
Author(s):  
W. F. Fahrig ◽  
D. L. Jones
Keyword(s):  
Volcanic Rocks ◽  
Pole Position ◽  
Canadian Shield ◽  
Paleomagnetic Data ◽  
Paleomagnetic Pole ◽  
Great Slave Lake ◽  
The Mean ◽  
Coppermine River ◽  
Age Determinations ◽  
Middle Proterozoic

North-northwesterly striking Mackenzie diabase dikes of middle-Proterozoic (Helikian) age are profuse in the western part of the Canadian Shield. Published paleomagnetic data on dikes of this trend in Mackenzie District, on the Muskox Intrusion, the Coppermine River volcanic rocks, and the Sudbury dikes suggest that they are all products of closely related igneous events. This paper presents paleomagnetic data that suggest that the intrusion of extensive diabase sheets in the East Arm of Great Slave Lake, and of dikes as far to the northeast as Melville Peninsula and as far to the southeast as Manitoba, were also parts of these events. The mean paleomagnetic pole position for the Mackenzie dikes and for related intrusive and extrusive rocks is [Formula: see text], 171 °W with [Formula: see text]. Radioactive age determinations, some of which are unpublished, indicate an age of about 1200 m.y. for the formation of these rocks. It is suggested that for convenience all of these apparently related intrusive and extrusive igneous episodes be referred to as Mackenzie igneous events.

Paleomagnetism of the Mealy Mountain Anorthosite Suite and of the Shabogamo Gabbro, Labrador, Canada

1974 ◽  
Vol 11 (1) ◽  
pp. 18-29 ◽  
Author(s):  
W. F. Fahrig ◽  
K. W. Christie ◽  
E. J. Schwarz
Keyword(s):  
Pole Position ◽  
Canadian Shield ◽  
The South ◽  
Clockwise Rotation ◽  
End Points ◽  
Stable Component ◽  
Sample Area ◽  
Initial Magnetization ◽  
East Component ◽  
Middle Proterozoic

Two stable, ancient, N.R.M. components were isolated by a.f. demagnetization of samples from 29 sites in the Helikian (Middle Proterozoic) anorthosite and adamellite suites of the Mealy Mountains. The directions of the two components are chiefly to the northwest, 20° upward (northwest component) and to the east, 65 °downward (east component). The northwest direction is thought to be the primary igneous T.R.M. and no reversely magnetized sites with this direction were encountered in the Mealy suite. The 11 sites from which the northwesterly component was isolated yielded a mean pole at 179 °W, 8 °N, α95 = 12°. This is some distance away from poles derived from rocks of comparable age from elsewhere in the Canadian Shield and may reflect a 50° clockwise rotation of this section of the Grenville Orogen relative to the Superior after the initial magnetization of the Mealy rocks. Evidence of a second stable component was found in 14 sites (east component); 11 of these are reversely magnetized and three are normally magnetized. The 14 sites with easterly (and reversed easterly) magnetization yielded a combined pole for this component at 182 °W, 38 °S, α95 = 9°. This pole position suggests that the east component was acquired after the rotation of this part of the Grenville Orogen. The cores from 3 sites exhibited two clear end-points during a.f. demagnetization and thus contain both the northwest and the east component.The Helikian Shabogamo Gabbro at the south end of the Labrador Trough was sampled at 13 sites on a line extending 80 km north from the Grenville Front. After a.f. cleaning these sites yielded a pole at 171 °W, 10 °N, α95 = 12°. This pole lies about 20° northwest of poles for rocks of similar age in the Superior Orogen so it is suggested that the rocks of the sample area, though lying a bit north of the line generally accepted as the 'Grenville Front', have been rotated clockwise (about 20°) since intrusion of the gabbro.

New Paleomagnetic Results from the Upper Belt – Purcell Supergroup of Alberta

1975 ◽  
Vol 12 (1) ◽  
pp. 52-61 ◽  
Author(s):  
M. E. Evans ◽  
D. K. Bingham ◽  
E. W. McMurry
Keyword(s):  
Pole Position ◽  
Canadian Shield ◽  
Considerable Potential ◽  
Paleomagnetic Pole ◽  
Belt Supergroup ◽  
Order Of Magnitude ◽  
Global Time ◽  
Geomagnetic Polarity ◽  
Apparent Conflict

Stable remanent directions have been obtained from fifteen sites located in the Purcell, Shepard and Kintla Formations of the upper Belt – Purcell Supergroup. The geomagnetic polarity sequence revealed by these and other studies suggests that the frequency of reversals was probably an order of magnitude lower than that observed over the last few million years. The polarity transitions have considerable potential as regional, and possibly, global, time lines for geological correlation.The paleomagnetic pole obtained (142 °W, 17 °S, dp = 4°, dm = 7°) agrees well with other results from the Belt Supergroup. It falls in a cluster of poles derived from various geological provinces of the Canadian Shield, which may imply that the shield was an integral unit as early as 1400 m.y. ago. However, the constancy of the pole position obtained from Belt rocks thought by some workers to be as young as 1100 m.y. conflicts with the large northward polar excursion (the Logan Loop) derived from other provinces. Possible explanations of this apparent conflict are discussed.

Paleomagnetism of the Franklin Diabases

1971 ◽  
Vol 8 (4) ◽  
pp. 455-467 ◽  
Author(s):  
W. F. Fahrig ◽  
E. Irving ◽  
G. D. Jackson
Keyword(s):  
Pole Position ◽  
Canadian Shield ◽  
Baffin Bay ◽  
Late Proterozoic ◽  
Paleomagnetic Pole ◽  
Early Tertiary ◽  
Davis Strait

Diabase intrusions, which have a probable mean age of 675 m.y., occur in a giant arc across the northern part of the Canadian Shield. They have a paleomagnetic pole position of 167° E, 8° N (α95 = 5°), and at least one reversal. The paleomagnetic results indicate that the northern Canadian Shield was near the equator at the time of intrusion, and this is in agreement with evidence of warm conditions of deposition found in erosional remnants of related late Proterozoic sediments. Some of the diabase, near the shores of Davis Strait, may have been partially remagnetized during the opening of Baffin Bay in the early Tertiary.

Pole Position for the Neohelikian Nemegosenda Carbonatite Complex, Ontario

1974 ◽  
Vol 11 (2) ◽  
pp. 341-345 ◽  
Author(s):  
D. T. A. Symons ◽  
J. Garber
Keyword(s):  
Pole Position ◽  
The Body ◽  
Paleomagnetic Data ◽  
Superior Province ◽  
Carbonatite Complex ◽  
Magnetization Direction ◽  
The Mean ◽  
Age Range

Paleomagnetic data from 17 sites (76 cores; 152 specimens) reveals that the Nemegosenda carbonatite complex retains a primary remanence magnetization of low stability. The pole position of 43 °N, 178 °W (P0.05: 15°, 24°) for the complex is concordant with a group of poles from other rock units in the Superior Province in the age range of 1000 to 1115 m.y. It is concluded that interpreting the 1036 m.y. K-Ar date as the age of emplacement of the complex is in agreement with the mean magnetization direction having been preserved without structural rotation since the body cooled.

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 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.

Proterozoic paleocurrents and depositional history of the East Arm fold belt, Great Slave Lake, Northwest Territories

1969 ◽  
Vol 6 (3) ◽  
pp. 441-462 ◽  
Author(s):  
Paul Hoffman
Keyword(s):  
Volcanic Rocks ◽  
Canadian Shield ◽  
Stratigraphic Correlation ◽  
Fold Belt ◽  
Axial Zone ◽  
Depositional History ◽  
Great Slave Lake ◽  
History Of ◽  
Three Stages ◽  
Fault Scarps

Nearly 40 000 ft (~12 190 m) of unmetamorphosed Aphebian (and possibly lowermost Helikian) sedimentary and volcanic rocks are exposed in the East Arm of Great Slave Lake. This sequence is an erosional remnant of an Appalachian-type geosynclinal complex with a NNW depositional strike. Integrated paleocurrent, stratigraphic, and sedimentological analysis reveals three stages in the depositional history of the complex: (1) a double transgressive, pre-orogenic miogeosyncline, which received sediment from a distant cratonic source to the ENE and which becomes thicker and more eugeosynclinal to the WSW; (2) a regressive, syn-orogenic exogeosyncline (clastic wedge), which received sediment from rapidly uplifted tectonic lands to the WSW; and (3) a continental, post-orogenic taphrogeosyncline (down-faulted intermontaine trough), which received sediment locally from block-fault scarps within the East Arm area.Facies predictions based on this model provide criteria for establishing stratigraphic correlation and contiguity between the East Arm and other Aphebian sequences in the northwestern Canadian Shield. The prevailing depositional strike is roughly perpendicular to the tectonic strike of the East Arm Fold Belt, and it should not therefore be assumed that depositional strike parallels tectonic strike in other belts. The Bear Province may have been the site of the orogenically active axial zone of the geosyncline, but that part of the Churchill Province near the East Arm remained passive until the final post-orogenic stage of sedimentation and may therefore be of epeirogenic origin.

Cambro-Ordovician paleomagnetic pole position and rubidium-strontium total rock isochron for charnockitic rocks from Mirnyy Station, East Antarctica

1972 ◽  
Vol 16 (3) ◽  
pp. 433-438 ◽  
Author(s):  
D MCQUEEN ◽  
C SCHARNBERGER ◽  
L SCHARON ◽  
M HALPERN
Keyword(s):  
Pole Position ◽  
East Antarctica ◽  
Paleomagnetic Pole
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