Paleomagnetism of Steel Mountain and Indian Head anorthosites from western Newfoundland

1976 ◽  
Vol 13 (1) ◽  
pp. 75-83 ◽  
Author(s):  
G. S. Murthy ◽  
K. V. Rao
Keyword(s):  
Northern Hemisphere ◽  
Remanent Magnetization ◽  
Canadian Shield ◽  
Relative Rotation ◽  
Southeastern Part ◽  
Lower Paleozoic ◽  
Grenville Province ◽  
Grenville Orogeny ◽  
Paleomagnetic Pole

As part of studies of anorthosites from the northern hemisphere, the paleomagnetism of two anorthosite inliers at Indian Head and Steel Mountain in western Newfoundland is described. The six sites at Indian Head retain a stable remanent magnetization and yield a paleomagnetic pole at 8 °S, 157½° E(δp = 15°, δm = 20°). This is close to poles for anorthositic and other rock units from within the Grenville Province that represent magnetization of age 1000 m. y., suggesting that there is no relative rotation between western Newfoundland and the southeastern part of the Canadian Shield, at least since the time of the Grenville orogeny. The ten sites at Steel Mountain also retain a stable magnetization, which yields a paleomagnetic pole at 22½° S, 41 °W (δp = 8°, δm = 14°). This position is closer to lower Paleozoic poles from Newfoundland and thus probably represents a lower Paleozoic magnetization.

The Paleomagnetism of Diabase Dikes from the Grenville Province

1971 ◽  
Vol 8 (7) ◽  
pp. 802-812 ◽  
Author(s):  
G. S. Murthy
Keyword(s):  
Primary Component ◽  
Low Temperature Oxidation ◽  
Grenville Province ◽  
Temperature Oxidation ◽  
Dike Swarm ◽  
Grenville Orogeny ◽  
Paleomagnetic Pole ◽  
Paleomagnetic Study ◽  
The Mean ◽  
Magnetic Stability

A paleomagnetic study was attempted of the diabase dike swarm intruding the Grenville structural province of the Canadian Shield. Both the alternating field and thermal demagnetization studies indicated that the dikes have varying degrees of stability of magnetization. Some dikes were shown to have stable primary component of magnetization. Microscopic observations indicated that, in most cases, the primary magnetic mineral titanomagnetite was altered to titanomaghemite, probably due to low temperature oxidation. A good correlation is obtained between magnetic stability and relative abundance of titanomagnetite to titanomaghemite in that dike. The mean paleomagnetic pole for the Grenville dike swarm, which is probably of late Precambrian age, was computed to lie at 3.0° N, 29.0° W with A25 = 11.0°. Comparison of this result with other Precambrian pole positions of similar age relative to North America suggests that the dikes were intruded after the Grenville orogeny.

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 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 the Callander Complex and the Cambrian apparent polar wander path for North America

1991 ◽  
Vol 28 (3) ◽  
pp. 355-363 ◽  
Author(s):  
D. T. A. Symons ◽  
A. D. Chiasson
Keyword(s):  
Remanent Magnetization ◽  
Pole Position ◽  
Canadian Shield ◽  
Complete Spectrum ◽  
Isothermal Remanent Magnetization ◽  
Alkaline Complex ◽  
Grenville Province ◽  
Polar Wander ◽  
The Core ◽  
Apparent Polar Wander Path

The 7 km2 circular Callander alkaline complex was emplaced into anorthositic and granitic gneisses of the Grenville Province in the Canadian Shield about 575 ± 5 Ma ago at the start of the Cambrian. The complex has not been subsequently metamorphosed or tilted. Detailed alternating-field and thermal step demagnetization of 252 specimens from 29 sites led to the identification of a characteristic A magnetization component with a direction of D = 82.2°, I = 82.7° (α95 = 3.1°, k = 83, N = 26 sites) in 5 sites of mesocratic to leucocratic syenite from the core of the complex, in 5 sites of fenitized host rock from its aureole, and in 16 sites of lamprophyre from radiating dikes. Isothermal remanent-magnetization tests show that the A component is retained by both magnetite and hematite in a complete spectrum of domain sizes. A reversals test suggests and a contact test shows the A component to be primary. Its pole position at 46.3°S, 121.4°E(dp = 5.9°, dm = 6.1°) does not fall on published but poorly defined Cambrian apparent polar wander paths, leading to speculation on an alternative Cambrian path.

The mid-Paleozoic deformation in the Hazen fold belt, Ellesmere Island, Arctic Canada

1990 ◽  
Vol 27 (10) ◽  
pp. 1359-1370 ◽  
Author(s):  
Eva M. Klaper
Keyword(s):  
Large Scale ◽  
Ellesmere Island ◽  
Small Scale ◽  
Northwestern Part ◽  
Fold Belt ◽  
Southeastern Part ◽  
Lower Paleozoic ◽  
Slip Mechanism ◽  
Fold Belts ◽  
Surface Geology

The mid-Paleozoic deformation of lower Paleozoic subgreenschist-facies sediments of the Hazen fold belt in northern Ellesmere Island is represented predominantly by chevron-style folding. Folded multilayers display cleavage fans suggesting synchronous fold and cleavage formation. Bedding-parallel slip indicates a flexural slip mechanism of folding. The geometry of several large-scale anticlinoria has been interpreted as being due to formation of these structures over detachments and thrust ramps.The constant fold geometry, the parallel orientation of faults and large- and small-scale folds, and the axial-plane foliation are related to a single phase of folding with a migrating deformation front in the Hazen fold belt during the mid-Paleozoic orogeny. The minimum amount of shortening in the Hazen and Central Ellesmere fold belts has been estimated from surface geology to increase from 40–50% of the original bed length in the external southeastern part to 50–60% in the more internal northwestern part of the belts.The convergent, thin-skinned nature of the Hazen and Central Ellesmere fold belts indicates that the postulated transpressive plate motions during the accretion of Pearya did not affect the study area.

Age of the Grenville dyke swarm, Ontario–Quebec: implications for the timing of lapetan rifting

1995 ◽  
Vol 32 (3) ◽  
pp. 273-280 ◽  
Author(s):  
S. L. Kamo ◽  
T. E. Krogh ◽  
P. S. Kumarapeli
Keyword(s):  
Long Range ◽  
Volcanic Rocks ◽  
Canadian Shield ◽  
Dyke Swarm ◽  
Alkaline Complex ◽  
Southeastern Part ◽  
Time Marker ◽  
Continental Breakup ◽  
Iapetus Ocean

U–Pb baddeleyite and zircon ages for three diabase dykes from widely spaced localities within the Grenville dyke swarm indicate a single age of emplacement at [Formula: see text] Ma. The 700 km long Grenville dyke swarm, located in the southeastern part of the Canadian Shield, was emplaced syntectonically with the development of the Ottawa graben. This graben may represent a plume-generated lapetan failed arm that developed at the onset of the breakup of Laurentia. Other precisely dated lapetan rift-related units, such as the Callander Alkaline Complex and the Tibbit Hill Formation volcanic rocks, indicate a protracted 36 Ma period of rifting and magmatism prior to volcanism along this segment of the lapetan margin. The age of the Grenville dykes is the youngest in a progression of precisely dated mafic magmatic events from the 723 Ma Franklin dykes and sills to the 615 Ma Long Range dykes, along the northern and northeastern margins of Laurentia, respectively. Thus, the age for these dykes represents a key time marker for continental breakup that preceded the formation of the Iapetus ocean.

The oxygen isotope composition of the surface crystalline rocks of the Canadian Shield

1978 ◽  
Vol 15 (11) ◽  
pp. 1773-1782 ◽  
Author(s):  
Yuch-Ning Shieh ◽  
Henry P. Schwarcz
Keyword(s):  
Isotope Composition ◽  
Crystalline Rocks ◽  
Canadian Shield ◽  
Granitic Rocks ◽  
Baffin Island ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Rock Types ◽  
Northern District ◽  
Basic Rocks

The average 18O/16O ratios of the major rock types of the surface crystalline rocks in different parts of the Canadian Precambrian Shield have been determined, using 47 composite samples prepared from 2221 individual rock specimens. The sampling areas include Baffin Island, northern and southwestern Quebec, Battle Harbour – Cartwright, northern District of Keewatin, Fort Enterprise, Snowbird Lake, Kasmere Lake, and Saskatchewan, covering approximately 1 400 000 km2. The granitic rocks from the Superior, Slave, and Churchill Provinces vary only slightly from region to region (δ18O = 6.9–8.4‰) and are significantly lower in 18O than similar rock types from the younger Grenville Province (δ = 9.2–10.0‰). The sedimentary and metasedimentary rocks have δ18O = 9.0–11.7‰ and hence are considerably lower than their Phanerozoic equivalents, possibly reflecting the presence of a high percentage of little-altered igneous rock detritus in the original sediments. The basic rocks in most regions fall within a δ18O range of 6.8–7.6‰, except in northern and southwestern Quebec where the δ-values are abnormally high (8.5–8.9‰). The overall average 18O/16O ratio of the surface crystalline rocks of the Canadian Shield is estimated to be 8.0‰, which represents an enrichment with respect to probable mantle derived starting materials by about 2‰.

THE MAGNETIZATION OF A ROCK CONTAINING MAGNETITE AND HEMOILMENITE

Geophysics ◽  
1964 ◽  
Vol 29 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Charles M. Carmichael
Keyword(s):  
Remanent Magnetization ◽  
Magnetic Moments ◽  
Canadian Shield ◽  
Titanium Oxides ◽  
Aeromagnetic Anomalies ◽  
X Ray ◽  
Lake Region ◽  
Unusual Occurrence

In areas such as the Canadian Shield, rocks often contain iron and titanium oxides with a remanent magnetization. These rocks can produce aeromagnetic anomalies that are positive, negative, or nonexistent depending on the magnitude and direction of the remanent component relative to that of the induced. In the Allard Lake region of Quebec there is a deposit containing up to 20 percent oxide that produces no anomaly detectable by either the airborne or ground magnetometer. Analyses of the rock by microscopic, magnetic, and X‐ray techniques have shown that it contains separate crystals of an almost pure magnetite and of exsolved hemoilmenite. The magnetite crystals are magnetized normally and the hemoilmenite crystals inversely. They are present in quantities such that their magnetic moments cancel and so produce no anomaly. While this is probably an unusual occurrence it shows that considerable care must be taken in regions where minerals having an inverse remanent magnetization may be present.

Mantle influence of syn- to late-Grenvillian alkaline magmatism in the Grenville Province: causes and implications

2017 ◽  
Vol 54 (3) ◽  
pp. 263-277 ◽  
Author(s):  
Lars Eivind Augland ◽  
Abdelali Moukhsil ◽  
Fabien Solgadi
Keyword(s):  
Orogenic Belt ◽  
Alkaline Magmatism ◽  
Magmatic Evolution ◽  
Grenville Province ◽  
Geochemical Composition ◽  
Magmatic Rocks ◽  
Grenville Orogeny ◽  
Slab Breakoff ◽  
Arc Setting ◽  
Laurentian Margin

Several features of Geon 10 magmatic evolution in the Grenville Orogenic Belt is difficult to reconcile with generally accepted models of protracted (ca. 100 Myr) continent–continent collision during the Grenville Orogeny. Particularly the presence of (partly) mantle-derived magmatic rocks, some with subduction signatures, intruded during the inferred climax of the orogeny, is not well accounted for in existing models. We present new geochemical, Lu–Hf isotopic and U–Pb geochronological data from three alkaline composite plutons in Quebec, Canada, that give important clues to the tectono-magmatic evolution from ca. 1040 to 1000 Ma of the Grenville Laurentian margin. The oldest pluton, emplaced at ca. 1038 Ma, has a geochemical composition compatible with derivation in an arc setting by partial melting of subcontinental lithospheric mantle. The two youngest plutons, emplaced at ca. 1014 and 1009 Ma, respectively, have typical within-plate geochemical signatures showing no obvious influence of subduction. The new and existing data indicate that much of the Grenville Laurentian margin experienced ensialic magmatism through large parts of Geon 10, an observation calling for alternative models to the existing to explain the Geon 10 evolution of the Grenville Orogenic Belt. We propose a model where Ottawan metamorphism and magmatism resulted from accretion of terranes and continued subduction beneath Laurentia until late Geon 10. Late Geon 10 magmatism could have been related to slab breakoff prior to or at the onset of a late Geon 10 collisional event, which has also been recently proposed based on paleomagnetic arguments.

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