Paleomagnetism of the Western Channel Diabase and Associated Rocks, Northwest Territories

1972 ◽  
Vol 9 (8) ◽  
pp. 960-971 ◽  
Author(s):  
E. Irving ◽  
J. A. Donaldson ◽  
J. K. Park
Keyword(s):  
Northwest Territories ◽  
Remanent Magnetization ◽  
Opposite Sign ◽  
Canadian Shield ◽  
Peak Amplitude ◽  
Preliminary Results ◽  
Late Precambrian ◽  
General Region

The stable remanent magnetization of the Western Channel diabase (1325–1785 m.y.) determined at 35 sites has a mean direction of 356, −50 (α95 = 6°) and a corresponding pole at 9 °N, 115 °W (A95 = 6°). Studies of rocks bordering the diabase show that this magnetization was acquired at the time of initial cooling. Preliminary results from older sediments, diabase, and porphyry (1770 m.y.) give directions of opposite sign, with corresponding poles in the same general region. These results, and others recently published, allow the path of apparent polar wandering, relative to the Canadian Shield, to be constructed in a preliminary fashion for the middle and earlier Proterozoic. This path, together with that previously obtained by other workers for the late Precambrian, suggests that during the Proterozoic the pole moved through two cycles of a roughly sinusoidal path with a peak-to-peak amplitude of about 90° of arc and a period of several hundred million years.

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.

scholarly journals Frozen subduction in Canada's Northwest Territories: Lithoprobe deep lithospheric reflection profiling of the western Canadian Shield

Tectonics ◽  
1999 ◽  
Vol 18 (1) ◽  
pp. 1-24 ◽  
Author(s):  
Frederick A. Cook ◽  
Arie J. van der Velden ◽  
Kevin W. Hall ◽  
Brian J. Roberts
Keyword(s):  
Northwest Territories ◽  
Canadian Shield

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.

scholarly journals Preliminary results of a magnetotelluric survey across the Brock Inlier, Northwest Territories

2016 ◽  
Author(s):  
J E Spratt ◽  
J A Craven ◽  
R H Rainbird
Keyword(s):  
Northwest Territories ◽  
Preliminary Results

Provenance of Paleozoic sedimentary rocks in the Canadian Cordilleran miogeocline: a Nd isotopic study

1997 ◽  
Vol 34 (12) ◽  
pp. 1603-1618 ◽  
Author(s):  
Carmala N. Garzione ◽  
P. Jonathan Patchett ◽  
Gerald M. Ross ◽  
JoAnne Nelson
Keyword(s):  
British Columbia ◽  
Northwest Territories ◽  
Middle Devonian ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Canadian Shield ◽  
Isotopic Study ◽  
Middle Ordovician ◽  
Southern Alberta ◽  
T Values

Nd isotopes and trace elements in sedimentary rocks of the Yukon, the Northwest Territories, and northern British Columbia are used to examine the source of sediments in the Canadian Cordilleran miogeocline. Previous Nd isotope studies in southern Alberta demonstrated that strata of Neoproterozoic to Late Ordovician age were derived from Archean and Proterozoic Canadian Shield sources, whereas by the Late Devonian, a shift of 6 εNd units to younger crustal sources (εNd (T) = −6 to −9) had occurred. In this study, we found that the shift to younger crustal Nd isotopic signatures in the Yukon and Northwest Territories occurred much earlier than in southern Alberta. Cambrian and older strata have εNd(T) values of −10.0 to −21.1, consistent with derivation from Canadian Shield sources. Lower Ordovician through Permian strata in the Yukon and Northwest Territories, including the Innuitian-derived Imperial Assemblage, have εNd(T) values of −5 to −11.4. In northern British Columbia, the shift to a younger source reflects a wider range of εNd(T) values, from -−8.7 to −14.6 in Middle Ordovician through Middle Devonian strata, suggesting continued input from Canadian Shield sources. By the Middle Devonian, a complete shift to younger crustal signatures (εNd(T) = −5.9 to −10.5) had occurred in northern British Columbia. Several sources for the more juvenile sediments include (1) a mixture of locally erupted volcanic rocks with Canadian Shield sources, (2) a Grenville source, and (3) an Innuitian source. We propose that Ordovician to Lower Devonian strata were derived from a mixture of locally erupted, juvenile volcanics and pre-Cambrian Canadian Shield sources, and post-Middle Devonian strata were sourced from the Innuitian orogen in the Canadian Arctic.

Shock-diminished paleomagnetic remanence at the Charlevoix impact structure, Quebec

1979 ◽  
Vol 16 (9) ◽  
pp. 1842-1856 ◽  
Author(s):  
P. Blyth Robertson ◽  
J. L. Roy
Keyword(s):  
Remanent Magnetization ◽  
Marginal Zone ◽  
Natural Remanent Magnetization ◽  
Significant Fraction ◽  
Magnetic Characteristics ◽  
Thermal Treatments ◽  
Magnetic Carrier ◽  
Impact Structure ◽  
Late Precambrian ◽  
Dual Polarity

The magnetic characteristics of shocked and unshocked anorthosites of the Charlevoix impact structure have been reexamined to assess the effects of high thermal and alternating field (af) cleaning treatments, and to evaluate any shock-induced features of the remanence in terms of mineralogy of the shocked rocks.From 16 sites, 197 specimens were subjected to stepwise thermal treatments to 710 °C, and a further 46 to incremental af cleaning to 290 mT. The 10 sites from the unshocked St-Urbain anorthosite carry a magnetization with unblocking temperatures (TUB) generally between 600–625 °C, with a significant fraction of remanence with TUB > 670 °C. Similarly, most of the remanence has a resistive coercive force (rcf) of 100–175 mT, with a significant fraction exceeding 290 mT. The remanence is carried by two exsolution phases of titano-hematite, with the later and more hematite-rich lamellae having the higher TUB and rcf. Although only one direction exists, at two sites where intensities are somewhat lower and some natural remanent magnetization (NRM) directions scattered, treatment reveals a dual polarity remanence. The pole (154°E, 02°S) obtained from these unshocked St-Urbain anorthosite sites falls on a well established segment of the late Precambrian apparent polar path of suitable age (≈950 Ma). Significant results could not be obtained from three additional sites in the marginal zone due to their ready acquisition of a viscous magnetization following thermal treatments.Data from two sites which display no shock effects and lie near the margin of the central uplift, and from one highly shocked sample from the crater centre show some possible effects of the shock event. All three have intensities substantially lower than in the St-Urbain sites, which is interpreted in the case of at least one of these sites as a shock-diminished remanence. A puzzling feature of the highly shocked samples is that the phase with a texture reminiscent of the ilmenite–hematite exsolution in the unshocked anorthosites, contains no iron. The remaining remanence, whose direction is parallel with that of the unshocked sites, is interpreted as pre-crater rather than shock-produced. Although many instances have been reported of a new shock-induced remanence imparted to rocks of equivalent and even lesser shock grade than those examined at Charlevoix, in all cases the magnetic carrier seems to have been magnetite. The lack of a shock-induced remanence at Charlevoix is attributed to the high TUB and rcf of hematite in these rocks.

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