Reconnaissance paleomagnetic study of igneous rocks from the eastern sector of the Labrador Trough

1985 ◽  
Vol 22 (11) ◽  
pp. 1561-1570
Author(s):  
Maurice K.-Seguin ◽  
Thomas Clark
Keyword(s):  
North America ◽  
Igneous Rocks ◽  
Polar Wander ◽  
Thermal Demagnetization ◽  
Eastern Sector ◽  
Paleomagnetic Study ◽  
Component C ◽  
The Mean ◽  
Three Components

A paleomagnetic study has been carried out on 75 samples of metagabbro and metaperidotite from 14 sites in the Labrador Trough. The sites were distributed over a distance of 500 km and are situated in sills intruded into formation near the top of the trough stratigraphic column. Four components (A, B, C, and D) were obtained after alternating field (AF) and thermal demagnetization. The mean directions of magnetization are A. 143°, +33°. α95 = 14.4°. k = 15.4, 8 sites: B, 69°, +51°, α95 = 10.3d, k = 22.9, 10 sites: C. 278°. +15°, α95 = 7.7°, k = 28, 14 sites; and D, 200°, +16°. α95 = 13.3°, k = 16.2, 9 sites. All components are secondary. The fold test is negative, and consequently no primary magnetization has been preserved in the isolated components. Component C may have erased all others in zones of highest metamorphism. The paleopoles obtained for components D, A, and C are, respectively, 270°E. 23°S (δP = 10°. δm = 18°); 327°E, 9°S (δp = 11°. δm = 20°); and I9°E, 11°S (antipole) (δp = 10°. δm = 17°). The paleopole positions obtained for these three components are compared with me existing late Aphebian and early Paleohelikian apparent polar wander (APW) path for North America and fall in the 1750–1850 Ma interval.

Étude paléomagnétique des roches protérozoïques de la formation de Sakami, région de la Grande Rivière, Territoire du Nouveau-Québec, Canada

1981 ◽  
Vol 18 (12) ◽  
pp. 1893-1899
Author(s):  
Maurice K. Seguin ◽  
Kamal N. M. Sharma ◽  
Gérard Woussen
Keyword(s):  
Magnetic Memory ◽  
Thermal Demagnetization ◽  
Paleomagnetic Study ◽  
Geological Formation ◽  
The Mean

We describe a paleomagnetic study of Mid-Proterozoic sandstone of the Sakami Formation. The thermal demagnetization is more effective than by alternating field; this indicates that part of the magnetic memory is located in hematite. The mean direction of magnetization after thermal and alternating field treatments is 031, −25 α95 = 7.1°, K = 73 and the corresponding paleopole position is 103°W, 18°S (dm = 11°, dp = 8°). These results are important because a part of this geological formation will be covered with water after completion of the development works of La Grande Rivière. [Journal Translation]

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.

Displacement of Vancouver Island: paleomagnetic evidence from the Karmutsen Formation

1980 ◽  
Vol 17 (9) ◽  
pp. 1210-1228 ◽  
Author(s):  
R. W. Yole ◽  
E. Irving
Keyword(s):  
North America ◽  
Vancouver Island ◽  
Late Triassic ◽  
Polar Wander ◽  
Apparent Polar Wander Path ◽  
Individual Site ◽  
Anticlockwise Rotation ◽  
Oriented Samples ◽  
Geomagnetic Fields ◽  
The Mean

New paleomagnetic results from the Karmutsen Formation (Late Triassic) of Vancouver Island confirm the presence of two families of magnetizations (X and Y), both of which are inconsistent with known Mesozoic and Cenozoic geomagnetic fields of cratonic North America. The X magnetizations have coherent directions with the exception of a subset of five sites (the B subset). We argue that the deviation of the B subset is caused either by a 31 ± 13 °anticlockwise rotation of a small block relative to the main sampling areas or by a short-term excursion of the field. The X magnetization has an overall mean direction 008°, −33 °α95 = 6 °based on results from 147 oriented samples (usually 2 specimens from each) collected at 28 sites spanning about 6000 m stratigraphically. We interpret this as the original Late Triassic magnetization. The corresponding X paleopole (21°N, 44°E A95 = 6°) is strongly far-sided and right-handed with respect to the Mesozoic apparent polar wander path for cratonic North America. The paleolatitude indicated for Vancouver Island in the Late Triassic is either 18°N or 18°S, the latter being preferred on the grounds that it yields a more consistent pattern for Cordilleran magnetizations, but the ambiguity is still not settled. In either case the results show that Vancouver Island was far south of its present position relative to North America in the Late Triassic, thus confirming the previous results of Irving and Yole. The Y magnetizations, with more heterogenous properties, occur at 14 sites (66 oriented cores, usually 2 specimens each). Y magnetizations are generally softer than X and for this and other reasons we regard them as secondary and post-Triassic in age. Individual site poles for the Y magnetization are, with minor exceptions, right-handed and slightly far-sided with respect to the apparent polar wandering path for cratonic North America. The mean paleopole for Y magnetizations is situated at 70°N, 15°W A95 = 11°. Both the X and Y magnetizations are consistent with either northward motion of the westernmost Cordilleran elements accompanied by clockwise rotation, or with oblique translation from the southwest. The northward component of motion derived from X directions would be the same in both instances and amounts to 1300 or 4900 km depending on whether the northern or the southern paleolatitude option is chosen. Our preference is for the latter and we present arguments which suggest that Vancouver Island may have been originally derived from a region near to eastern Gondwana or from a block east of Gondwana that might have included Malaysia. The procedures used for the tectonic analysis of aberrant paleopoles are described in the Appendix.

scholarly journals Rotation of the Philippine Sea plate inferred from paleomagnetism of oriented cores taken with an ROV-based coring apparatus

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Toshitsugu Yamazaki ◽  
Shun Chiyonobu ◽  
Osamu Ishizuka ◽  
Fumisato Tajima ◽  
Naoki Uto ◽  
...  
Keyword(s):  
Plate Motion ◽  
Philippine Sea Plate ◽  
Late Oligocene ◽  
Clockwise Rotation ◽  
Polar Wander ◽  
Philippine Sea ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Study ◽  
History Of ◽  
The Mean

AbstractReconstructing the history of Philippine Sea (PHS) plate motion is important for better understanding of the tectonics of the surrounding plates. It is generally considered that the PHS plate migrated northward since Eocene, but its rotation has not been constrained well; some reconstructions incorporated a large clockwise rotation but others did not. This is mainly because the difficulty of collecting oriented rocks from the mostly submerged PHS plate hindered establishing an apparent polar wander path. In this study, we conducted a paleomagnetic study of oriented cores taken using an ROV-based coring apparatus from the Hyuga Seamount on the northern part of the Kyushu-Palau Ridge, a remnant arc in the stable interior of the PHS plate. Stepwise thermal and alternating-field demagnetizations were applied to specimens taken successively from two ~ 30 cm long limestone cores of middle to late Oligocene age, and characteristic remanent magnetization directions could be isolated. Declination and inclination of D = 51.5° and I = 39.8°, respectively, were obtained as the mean of the two cores. The easterly-deflected declination means ~ 50° clockwise rotation of the PHS plate since middle to late Oligocene. In addition, ~ 5° latitudinal change of the site is estimated from the mean inclination. The result implies that the Kyushu-Palau Ridge was located to the southwest of the present position in middle to late Oligocene, and that PHS plate rotation as well as the Shikoku and Parece Vela Basin spreading contributed to the eastward migration of the Izu-Ogasawara (Bonin) Arc to the current position.

PREDATION BY INSECTS AND SPIDERS INHABITING COLONIAL WEBS OF HYPHANTRIA CUNEA

1972 ◽  
Vol 104 (8) ◽  
pp. 1197-1207 ◽  
Author(s):  
R. F. Morris
Keyword(s):  
Population Dynamics ◽  
Nova Scotia ◽  
North America ◽  
Population Density ◽  
New Brunswick ◽  
Numerical Response ◽  
Initial Number ◽  
Hyphantria Cunea ◽  
The North ◽  
The Mean

AbstractThe number of predators inhabiting nests of Hyphantria cunea Drury was recorded annually for 13 years in four areas in New Brunswick and two areas on the coast of Nova Scotia. The most common groups were the pentatomids and spiders, which sometimes reproduced within the nests, but the mean number per nest was low in relation to the number of H. cunea larvae in the colonies. The rate of predation on fifth-instar larvae was low. Small or timid predators appeared to prey largely on moribund larvae or small saprophagans during the principal defoliating instars of H. cunea.No relationship could be detected between the number of larvae reaching the fifth instar and the number of predators in the colony; nor could any functional or numerical response of the predators to either the initial number of larvae per colony or the population density of colonies be found. It is concluded that the influence of the nest-inhabiting predators is small and relatively stable, and may be treated as a constant in the development of models to explain the population dynamics of H. cunea.H. cunea is a pest in parts of Europe and Asia, where it has been accidentally introduced from North America. The introduction to other continents of the North American predator, Podisus maculiventiis (Say), is discussed briefly.

scholarly journals Genetic studies revealed differences between European and North American populations of Calypogeia azurea

2016 ◽  
Vol 42 (1) ◽  
pp. 19-26 ◽  
Author(s):  
Katarzyna Buczkowska ◽  
Alina Bączkiewicz ◽  
Patrycja Gonera
Keyword(s):  
Genetic Variation ◽  
North America ◽  
Genetic Distance ◽  
Gene Diversity ◽  
Oil Bodies ◽  
Genetic Studies ◽  
Isozyme Loci ◽  
The Mean ◽  
Different Parts ◽  
Nei's Genetic Distance

Abstract Calypogeia azurea, a widespread, subboreal-montane liverwort species, is one of a few representatives of the Calypogeia genus that are characterized by the occurrence of blue oil bodies. The aim of the study was to investigate the genetic variation and population structure of C. azurea originating from different parts of its distribution range (Europe and North America). Plants of C. azurea were compared with C. peruviana, another Calypogeia species with blue oil bodies. In general, 339 gametophytes from 15 populations of C. azurea were examined. Total gene diversity (HT) estimated on the basis of nine isozyme loci of C. azurea at the species level was 0.201. The mean Nei’s genetic distance between European populations was equal to 0.083, whereas the mean genetic distance between populations originating from Europe and North America was 0.413. The analysis of molecular variance (AMOVA) showed that 69% of C. azurea genetic variation was distributed among regions (Europe and North America), 15% - among populations within regions, and 16% - within populations. Our study revealed that C. azurea showed genetic diversity within its geographic distribution. All examined samples classified as C. azurea differed in respect of isozyme patterns from C. peruviana.

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.

Abstract TP397: Clinical And Functional Outcome Of Adult Patients Diagnosed With Moyamoya Disease In Childhood

Stroke ◽  
2017 ◽  
Vol 48 (suppl_1) ◽  
Author(s):  
David Fam ◽  
Nomazulu Dlamini ◽  
Cheryl Jaigobin
Keyword(s):  
Ischemic Stroke ◽  
North America ◽  
Natural History ◽  
Functional Outcome ◽  
Moyamoya Disease ◽  
Vascular Event ◽  
Moyamoya Syndrome ◽  
The Mean

Background: Moyamoya disease is a progressive occlusive arteriopathy of the terminal ICA and its branches, leading to the formation of unstable collateral vessels. The disease is found worldwide, and is associated with a number of predisposing conditions, termed moyamoya syndrome. Currently there is a paucity of data on the natural history of moyamoya disease in North America, especially the long-term outcome of pediatric moyamoya. Objective: Our objectives were to determine the rate of recurrent TIA, ischemic stroke and intracerebral hemorrhage in patients presenting with pediatric Moyamoya disease and to assess long-term functional outcome. Methods: This study was a retrospective chart review of 52 patients presenting with pediatric moyamoya disease. We included patients aged 18 or older with a diagnosis of moyamoya disease or syndrome. All patients had confirmatory baseline vascular imaging (MRA or CTA +/- cerebral angiography). Baseline demographic variables and annual vascular event recurrence risk were obtained from the records. Modified Rankin Score (MRS) at presentation and last follow-up were determined from clinical records. Results: Of the original cohort, 34 patients were included for analysis. The mean age of the patients was 23.9 years. The mean age at presentation was 9 years (SD=4) with an average follow-up of 11.3 years (SD=5.1) for a total of 383 patient years. There was slight female predominance (1.4:1). Fifty percent of patients (17) presented with ischemic stroke. A total of 26 patients (76%) underwent surgery, with 7 (21%) requiring repeat surgery. The annual vascular recurrent event rate was 5.0% (19/383), which was not significantly different between surgical and non-surgical groups or between different moyamoya syndrome subtypes. Most of the recurrent events were TIA (annual recurrence 3.7%). There was no significant difference between initial MRS, MRS at last follow-up and mean change in MRS between surgical and non-surgical groups. Conclusion: Our study is the largest North American natural history study of pediatric moyamoya. Our observations indicate that pediatric moyamoya in North America have low recurrent vascular event rates and long-term functional outcomes are good, even in conservatively managed patients.

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