Paleomagnetism of pre-Grenvillian mafic intrusions from the Grenville Province, southeast Labrador

1989 ◽  
Vol 26 (12) ◽  
pp. 2541-2555 ◽  
Author(s):  
G. Murthy ◽  
C. F. Gower ◽  
M. Tubrett ◽  
R. Pätzold
Keyword(s):  
Layered Intrusions ◽  
Characteristic Direction ◽  
Heating Pulse ◽  
Grenville Province ◽  
Polar Wander ◽  
Mafic Intrusions ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Layered Mafic Intrusion ◽  
Middle Proterozoic

Paleomagnetic results are reported for Middle Proterozoic layered intrusions and dykes from within the Grenville Province of coastal southeastern Labrador. Rock units studied include the Little Grady Island layered norite intrusion, crosscutting mafic dykes from Little Grady Island, the dated Michael Gabbro from Double Island, and other miscellaneous mafic intrusions. On the basis of mineralogy and composition, it is concluded that the Little Grady Island layered mafic intrusion, the crosscutting dykes from Little Grady Island, and the miscellaneous mafic intrusions belong to the same period of magmatism (ca. 1650 Ma), in contrast with the Michael Gabbro, which belongs to a later event (ca. 1426 Ma).All rock units (except two dykes from the Hawke River Terrane) yield similar directions of magnetization. The remanence is extremely stable and has a characteristic direction of declination (D) = 321.7 °and inclination (I) = −49.3 °(N = 20, k = 24.1, α95 = 6.8°), with corresponding paleopole at 0.1°N, 155.1°E. This paleopole is interpreted as being representative of Grenvillian remagnetization. Based on an earlier age-calibrated Grenville track of the North American apparent polar wander path, this magnetization is correlated with a 900 Ma event, probably a (heating) pulse superposed on the general Grenvillian cooling. In contrast with this regional behaviour, two dykes from the Hawke River Terrane (Earl Island) yield a characteristic remanence of D = 285.7 °and I = 6.6°, with corresponding pole at 12°N, 158°W, interpreted as acquired during pre-Grenvillian, probably Elsonian, resetting.

Pre-Grenvillian and Grenvillian lithotectonic regions in eastern Labrador—correlations with the Sveconorwegian Orogenic Belt in Sweden

1984 ◽  
Vol 21 (6) ◽  
pp. 678-693 ◽  
Author(s):  
Charles F. Gower ◽  
Victor Owen
Keyword(s):  
Orogenic Belt ◽  
Grenville Province ◽  
Pluton Emplacement ◽  
Mafic Intrusions ◽  
The North ◽  
Rock Types ◽  
Structural Style ◽  
Opening And Closing ◽  
Layered Mafic Intrusions ◽  
Middle Proterozoic

The Trans-Labrador batholith, Groswater Bay Terrane, and Lake Melville Terrane are three major crustal segments located adjacent to or within the Grenville Province in eastern Labrador. Each crustal segment is a distinct lithotectonic entity displaying contrasts with each other in proportions of rock types, structural style, and metamorphic imprint. Together they indicate a unilateral polarity to the region, partly reflecting Grenvillian tectonism, which sliced the region into thrust-bound blocks.In all three crustal segments, an Archean or Aphebian gneissic basement is inferred onto or adjacent to which ca. 1900–1700 Ma supracrustal rocks were deposited. Deformation, metamorphism, and granitoid pluton emplacement were partly coeval with and partly postdated the supracrustal assemblages. In the north, tectonothermal effects can be assigned to Hudsonian–Ketilidian orogenesis but their peak was 50–100 Ma later farther south. Post-tectonic granitoid plutons and layered mafic intrusions were emplaced at about 1650–1600 Ma, and further pulses of mafic intrusion occurred prior to the Grenvillian Orogeny.Comparison with the Sveconorwegian Orogenic Belt in southern Sweden shows remarkable similarities in lithologies, geological histories, and structural style. The Småland–Värmland granitoid belt, Eastern Pregothian mega-unit, and Western Pregothian mega-unit are interpreted here to be the Scandinavian counterparts of the Trans-Labrador batholith, Groswater Bay Terrane, and Lake Melville Terrane, respectively. This correlation is taken to indicate that both regions were part of the same tectonic margin during Middle Proterozoic times.The implication of this correlation is that the opening and closing of the lapetus Ocean resulted in a 2000 km sinistral "offset" of the Grenvillian–Sveconorwegian Front and other Precambrian features on either side of the Caledonides suture.

Paleomagnetism of the Lac St-Jean anorthosite and related rocks, Grenville Province, Quebec

1983 ◽  
Vol 20 (2) ◽  
pp. 246-258 ◽  
Author(s):  
K. L. Buchan ◽  
W. F. Fahrig ◽  
G. N. Freda ◽  
R. A. Frith
Keyword(s):  
North American ◽  
Regional Metamorphism ◽  
The Other ◽  
Central Portion ◽  
Grenville Province ◽  
Polar Wander ◽  
Thermal Demagnetization ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Normal Polarity

Alternating field and thermal demagnetization study of the Lac St-Jean anorthosite and related rock units in the central portion of the exposed Grenville Province reveals two components of magnetization, one of reversed and the other of normal polarity. Both components are thought to have been acquired during the last regional metamorphism, which was sufficiently intense in this area (mostly amphibolite grade) to reset any earlier magnetization. Corresponding paleopoles at 193°W, 8°S (dm = 7.3°, dp = 4.6°) and 213°W, 19°S (dm = 10.5°, dp = 8.5°) lie along the 950–900 Ma segment of the recently calibrated Grenville track of the North American apparent polar wander path, a track that has thus far been defined largely by results from rock units of the western Grenville.

Preliminary Proterozoic apparent polar wander paths for the South China Block and their tectonic implications

1998 ◽  
Vol 35 (3) ◽  
pp. 302-320 ◽  
Author(s):  
Huimin Zhang
Keyword(s):  
South China ◽  
North China ◽  
Eastern China ◽  
North China Block ◽  
Polar Wander ◽  
Late Proterozoic ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Study ◽  
Middle Proterozoic

Results of a regional paleomagnetic study of Precambrian rocks in central-east China are summarized and interpreted. The study is a partial outcome of a geoscience transect incorporating three terranes, namely the Yangzi, Jiangnan, and Huaxia blocks. Paleomagnetic poles derived from a range of metamorphic, igneous, and sedimentary rocks define a northeast to southwest swath crossing the present Pacific Ocean and interpreted to embrace Early to Late Proterozoic times. All three terranes define segments of the same swath and correlate with a similar apparent polar wander path previously defined from the North China Block. The results imply that the constituent blocks of eastern China formed a united block during Early to Middle Proterozoic times. Later relatively large fragmentation is confirmed by Late Proterozoic apparent polar wander path records of the North China and South China Blocks.

Paleomagnetism of the Lawrenceton Formation volcanic rocks, Silurian Botwood Group, Change Islands, Newfoundland

1989 ◽  
Vol 26 (2) ◽  
pp. 296-304 ◽  
Author(s):  
Julie E. Gales ◽  
Ben A. van der Pluijm ◽  
Rob Van der Voo
Keyword(s):  
North American ◽  
Volcanic Rocks ◽  
Mobile Belt ◽  
Structural Mapping ◽  
Polar Wander ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Study ◽  
North American Craton

Paleomagnetic sampling of the Lawrenceton Formation of the Silurian Botwood Group in northeastern Newfoundland was combined with detailed structural mapping of the area in order to determine the deformation history and make adequate structural corrections to the paleomagnetic data.Structural analysis indicates that the Lawrenceton Formation experienced at least two folding events: (i) a regional northeast–southwest-trending, Siluro-Devonian folding episode that produced a well-developed axial-plane cleavage; and (ii) an episode of local north-trending folding. Bedding – regional cleavage relationships indicate that the latter event is older than the regional folding.Thermal demagnetization of the Lawrenceton Formation yielded univectorial southerly and shallow directions (in situ). A fold test on an early mesoscale fold indicates that the magnetization of the Botwood postdates this folding event. However, our results, combined with an earlier paleomagnetic study of nearby Lawrenceton Formation rocks, demonstrate that the magnetization predates the regional folding. Therefore, we conclude that the magnetization occurred subsequent to the local folding but prior to the period of regional folding.While a tectonic origin for local folding cannot be entirely excluded, the subaerial nature of these volcanics, the isolated occurrence of these folds, and the absence of similar north-trending folds in other areas of eastern Notre Dame Bay suggest a syndepositional origin. Consequently, the magnetization may be nearly primary. Our study yields a characteristic direction of D = 175°, I = +43°, with a paleopole (16°N, 131 °E) that plots near the mid-Silurian track of the North American apparent polar wander path. This result is consistent with an early origin for the magnetization and supports the notion that the Central Mobile Belt of Newfoundland was adjacent to the North American craton, in its present-day position, since the Silurian.

Paleomagnetism of the komatiitic basalts of the Ottawa Islands, N.W.T.

1985 ◽  
Vol 22 (4) ◽  
pp. 553-566 ◽  
Author(s):  
K. L. Buchan ◽  
W. R. A. Baragar
Keyword(s):  
North American ◽  
Hudson Bay ◽  
The West ◽  
Magnetization Direction ◽  
Polar Wander ◽  
The North ◽  
Dominant Component ◽  
Apparent Polar Wander Path

The komatiitic basalts of the Ottawa Islands in eastern Hudson Bay are on strike with and believed to form a continuation of similar units of the Cape Smith Belt 150 km to the northeast. Units sampled in the Ottawa Islands all dip gently to the west and hence are not suitable for an internal fold test of their age of magnetization. However, before correcting for the tilt of the lavas, the dominant magnetization direction (D = 207.6°, I = 61.9°, k = 168, α95 = 3.7°) does not differ significantly from the uncorrected magnetization direction reported from the steeply dipping, northwest-facing units at Cape Smith (D = 218°, I = 60°, k = 47, α95 = 4°). This negative fold test suggests that the remanence at both locations was acquired after folding. Comparison with the North American Precambrian apparent polar wander path implies that overprinting is related to the Hudsonian Orogeny.A second stable magnetization directed to the west with a shallow inclination is superimposed on the dominant component at a number of sampling sites. Its direction is poorly defined and no fold test is possible. However, magnetic evidence suggests that this component was probably acquired as an overprint after the dominant magnetization, perhaps during a mild reheating associated with the Elsonian Orogeny.

Age of the Firesand River carbonatite complex from paleomagnetism

1989 ◽  
Vol 26 (11) ◽  
pp. 2401-2405 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
Remanent Magnetization ◽  
Pole Position ◽  
Blocking Temperature ◽  
Isothermal Remanent Magnetization ◽  
Carbonatite Complex ◽  
Polar Wander ◽  
Partial Contact ◽  
Apparent Polar Wander Path ◽  
Temperature Spectra ◽  
Middle Proterozoic

The 2.3 km diameter Firesand River complex intrudes Archean volcanics and granites of the Wawa Subprovince in the Superior Province about 8 km east of Wawa, Ontario. It has given differing Middle Proterozoic K–Ar biotite ages of 1018 ± 50 and 1097 Ma. Alternating-field and thermal step demagnetization of specimens from three calcific carbonatite sites, five ferruginous dolomitic carbonatite sites, and one lamprophyre dike site isolated a stable mean direction of 290°, 33 °(α95 = 12°). Isothermal remanent magnetization tests indicate the remanence is held by single-to pseudosingle-domain magnetite and hematite in the carbonatite. The dike remanence is Keweenawan in age, thereby confirming its genetic relationship to the complex, and it gives a positive partial contact test with its host rock, indicating no postintrusive remagnetization. The blocking-temperature spectra indicate that postintrusive uplift has not exceeded about 4 km. The pole position for the complex is 183°E, 27°N (dp = 8°, dm = 13°). This pole lies directly on the well-dated Keweenawan apparent polar wander path, giving an age of 1090 ± 10 Ma, in agreement with the older K–Ar age. It also confirms geologic and aeromagnetic evidence that the complex has not been tectonically tilted since emplacement.

scholarly journals The Apparent Polar Wander Path For the North China Block Since the Jurassic

1991 ◽  
Vol 104 (1) ◽  
pp. 29-40 ◽  
Author(s):  
Zhong Zheng ◽  
Masaru Kono ◽  
Hideo Tsunakawa ◽  
Gaku Kimura ◽  
Qingyun Wei ◽  
...  
Keyword(s):  
North China ◽  
North China Block ◽  
Polar Wander ◽  
The North ◽  
Apparent Polar Wander Path

Paleomagnetism of the Abitibi dyke swarm, southern Superior Province, and implications for the Logan Loop

1993 ◽  
Vol 30 (9) ◽  
pp. 1886-1897 ◽  
Author(s):  
Richard E. Ernst ◽  
Kenneth L. Buchan
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Dyke Swarm ◽  
Earth’S Magnetic Field ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Earth's Magnetic Field ◽  
Reversed Polarity ◽  
Magma Pulses ◽  
Middle Proterozoic

The trace of the Middle Proterozoic Logan Loop of the North American apparent polar wander path is controversial. The older 1270–1110 Ma limb of the loop is poorly constrained, while the depth of the loop, based on the 1110–1080 Ma Keweenawan data of the younger limb, is thought by some to be largely an artifact of reversal asymmetry in the Earth's magnetic field. Paleomagnetism of the 1141 Ma Abitibi mafic dyke swarm is one of the keys to constraining the geometry of the Logan Loop.Unfortunately, previous paleomagnetic studies failed to distinguish dykes of the northeast-trending Middle Proterozoic olivine-bearing Abitibi swarm from subparallel Early Proterozoic olivine-free Biscotasing (formerly Preissac) dykes, and hence paleomagnetic poles determined in these studies should no longer be used. In the present study, sampling of eight Abitibi dykes has identified 23 normally magnetized sites in four dykes and, for the first time, five reversely magnetized sites in three dykes. One of the normally magnetized sites corresponds to the locality for which a high-precision U–Pb age was previously reported. A baked contact test establishes that the characteristic remanence of one normally magnetized dyke is primary. In addition, sites along individual dykes exhibit much smaller secular variation than is observed between dykes, indicating that the remanences of the other dykes are also primary. One of the normally magnetized dykes, the 700 km long Great Abitibi dyke, exhibits two primary directions that correspond to two geochemically distinct magma pulses. The five normally magnetized units, which consist of four separate dykes plus the second pulse of the Great Abitibi dyke, yield a well-defined mean paleomagnetic pole at 42.8°N, 151.5°W, dm = 16.3°, dp = 12.5°. It falls close to the reversely magnetized poles from the Keweenawan Track and establishes a minimum depth for the Logan Loop of about 40°. The reversed-polarity data from three other dykes are more scattered and may not average out secular variation. Hence, the present study is inconclusive regarding asymmetry of the Earth's magnetic field at 1141 Ma, even though a mean pole based on combined normal-and reversed-polarity dykes is indistinguishable from that based on normal-polarity dykes alone.

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