Palaeomagnetic evidence bearing on the evolution of the Canadian Cordillera

1990 ◽  
Vol 331 (1620) ◽  
pp. 487-509 ◽  
Keyword(s):  
North America ◽  
Canadian Cordillera ◽  
Present Position ◽  
The South ◽  
The West ◽  
Western Cordillera ◽  
Palaeomagnetic Data ◽  
Comparable Magnitude ◽  
Bedded Rocks

Palaeomagnetic data from Permian, Triassic and Jurassic bedded rocks, to which attitudinal corrections can be applied, yield palaeolatitudes concordant with those of ancestral North America, but very large predominantly anticlockwise rotations about vertical axes. Data from Cretaceous rocks yield apparent palaeolatitudinal displacements that increase westward. Small or negligible displacements are obtained from the Omineca Belt. Intermediate displacements (1000-2000 km) from the Intermontane Belt, are based on data from Cretaceous bedded sequences. Further to the west in the Coast Belt, larger apparent displacements (greater than 2000 km) have been obtained from plutons for which no attitudinal control is yet available. Data from Eocene rocks are concordant. Possibilities to consider are as follows: (a) little or no displacement and tilting to the southwest at about 30°; (b) large (greater than 2000 km in the Coast Belt) northward displacement since mid-Cretaceous time preceded by southward displacement of comparable magnitude in Juro-Cretaceous time; (c) lesser (1000-2000 km) overall displacement coupled with variable and lesser tilts to the south and southeast of plutons of the Coast Belt. Under hypothesis (a) the western Cordillera was formed and has remained in approximately its present position relative to ancestral North America; data from bedded volcanics of the Intermontane Belt are not consistent with this hypothesis. From the evidence currently available we favour hypotheses (b) or (c), although more data from bedded sequences are required. It is noteworthy that hypotheses (a) and (c) predict tilt directions that differ by about 90° and hence ought to be distinguishable by geological studies.

Magnetism and age of the Porteau Pluton, southern Coast Belt, British Columbia: evidence for tilt and translation

1995 ◽  
Vol 32 (4) ◽  
pp. 380-392 ◽  
Author(s):  
E. Irving ◽  
J. Baker ◽  
N. Wright ◽  
C. J. Yorath ◽  
R. J. Enkin ◽  
...  
Keyword(s):  
British Columbia ◽  
North America ◽  
Coercive Force ◽  
The Body ◽  
Canadian Cordillera ◽  
Southern Coast ◽  
The South ◽  
The West ◽  
Zircon Age ◽  
Minimum Estimate

The Porteau Pluton is a variably foliated quartz diorite to granodiorite intrusion in the southern Coast Belt of the Canadian Cordillera (49.6°N, 123.2°W). 40Ar/39Ar ages are 95 ± 5 Ma from biotite and 101.5 ± 0.7 Ma from hornblende, which, together with an earlier U–Pb zircon age of 100 ± 2 Ma, indicate that the body was emplaced, uplifted, and cooled rapidly in mid-Cretaceous time. The rocks contain high coercive force (hard) remanent magnetizations with unblocking temperatures between 500 and 600 °C, close to those of Ar in hornblende, indicating that remanence was acquired at or close to the hornblende plateau age. The hard remanence directions have an elongate distribution, in agreement with the predictions of M.E. Beck regarding magnetization acquired during tilting, uplift, and cooling of plutons. No part of the distribution agrees with the direction expected from observations from rocks of mid-Cretaceous age from cratonic North America. The elongate distribution defines the axis of tilt (347° east of north) but not its direction; tilt could have been down toward the east or down toward the west. The former yields an inclination that is 29.0 ± 4.9° shallower than expected from cratonic observations, corresponding to a displacement from the south of 3200 ± 500 km. The latter reconstruction yields an inclination that is anomalously shallow by 14.8 ± 3.9°, corresponding to a displacement from the south of 1600 ± 400 km, which is a minimum estimate. It is argued, therefore, that the Porteau Pluton has undergone both tilt and displacement from the south by distances substantially in excess of 1000 km.

Paleopoles and paleolatitudes of North America and speculations about displaced terrains

1979 ◽  
Vol 16 (3) ◽  
pp. 669-694 ◽  
Author(s):  
E. Irving
Keyword(s):  
North America ◽  
Plate Tectonics ◽  
Early Carboniferous ◽  
Coast Range ◽  
Present Position ◽  
Polar Wander ◽  
The Past ◽  
Western Cordillera ◽  
Middle Paleozoic ◽  
Single Path

A statistically determined path of apparent polar wander for the past 300 Ma for North America is given. It has a zigzag form, the bends corresponding to important changes in the drift of North America. Many Mesozoic and Early Tertiary paleopoles from the Western Cordillera do not conform to this path, and they are best explained by motions of miniblocks within the Cordillera. Especially notable is the displacement of Vancouver Island and associated Alaskan terrains (Wrangellia) in the early Mesozoic, and the clockwise rotation of the Coast Range of Oregon and Washington (Siletzia) in the Cenozoic. Limited evidence indicates that part at least of the Northern Appalachian region could have been about 10° south of its present position relative to North America in Late Devonian and Early Carboniferous times, and that it achieved its present position by Late Carboniferous time. Displaced terrains of early and middle Paleozoic age may also be present in the Appalachians. Displacements in the Appalachians and Cordillera could have been caused by the exchange of fragments of continental crust across transcurrent plate junctures. Apparent polar wandering paths for the Precambrian are tentative, but a fairly simple single path can be constructed for all structural provinces of the Laurentian Shield. This reconstruction of a single Precambrian path is supported by agreement among approximately contemporaneous paleopoles from widespread localities. It implies that movements amongst the structural provinces of the shield during the Hudsonian and Grenvillian Orogenies have been modest, and perhaps not in excess of about 1000 km in a latitude sense. This idea has been disputed by those who would apply conventional ideas of plate-tectonics to the Proterozoic, but it has the merit of explaining all the paleopoles and their geological relationships in a comparatively simple unified scheme. Rates of latitude change in the Precambrian may have been over twice as great as in the Phanerozoic.

Kilometre-scale folding in the Teslin zone, northern Canadian Cordillera, and its tectonic implications for the accretion of the Yukon-Tanana terrane to North America

1999 ◽  
Vol 36 (3) ◽  
pp. 479-494 ◽  
Author(s):  
Martin de Keijzer ◽  
Paul F Williams ◽  
Richard L Brown
Keyword(s):  
North America ◽  
Shear Zone ◽  
North American ◽  
Root Zone ◽  
Fault System ◽  
Canadian Cordillera ◽  
The West ◽  
The North ◽  
South Central ◽  
North American Craton

The Teslin zone in south-central Yukon has previously been described as a discrete zone with a steep foliation unique to the zone. It includes the Anvil assemblage and the narrowest portion of the Yukon-Tanana terrane (the Nisutlin assemblage), and is defined by post-accretionary faults: the Big Salmon fault to the west and the d'Abbadie fault system to the east. The zone was interpreted as a lithospheric suture or a crustal-scale transpression zone, and as the root zone of klippen lying on the North American craton to the east. We demonstrate that deformation and metamorphism are the same inside and outside the zone. The steep transposition foliation in the zone, in contrast to adjacent rocks to the east, coincides with the steep limb of a regional F3 structure. This fold has a shallow limb in the easternmost part of the zone and immediately east of the zone. Thus we reject earlier interpretations. If a suture exists between the obducted Anvil and Yukon-Tanana Nisutlin assemblages and North America, it is a shear zone that occurs at the base of the obducted rocks, which has been folded by the F3 fold. However, evidence that this thrust boundary is a lithospheric suture is lacking. A consequence of our interpretation is that North American rocks pass under the eastern Teslin zone and outcrop to the west of the Nisutlin and Anvil assemblages. This geometry precludes the possibility of the Teslin zone being the root zone of the klippen.

Correlation of mid-Cretaceous granites with source terranes in the northern Canadian CordilleraLithoprobe Publication 1475.

2008 ◽  
Vol 45 (3) ◽  
pp. 389-403 ◽  
Author(s):  
George A. Morris ◽  
Robert A. Creaser
Keyword(s):  
Trace Elements ◽  
North America ◽  
Published Data ◽  
Isotopic Ratios ◽  
Canadian Cordillera ◽  
The West ◽  
Data Set ◽  
Tectonic Zone ◽  
Growing Body ◽  
Accreted Terranes

This study presents a broad geochemical and isotopic synthesis of mid-Cretaceous granites in the southern Yukon as well as a comparative data set for granites sourced from, and hosted by, accreted terranes in the west through to ancient cratonic rocks in the east. We present data from a traverse perpendicular to the strike of the northern Canadian Cordillera allowing comparison with the growing body of such data derived from the host terranes. Trace elements, specifically the “subduction signature,” allow the discrimination of oceanic verses continental crustal sources. Comparison of isotopic ratios of Sr and, particularly, Nd with published data further refine the correlation of granites with their source terranes. Granites are initially divided based upon their host morphogeological belts, however, our study indicates that the source terranes transcend these traditional boundaries. For Intermontane Belt hosted granites three distinct sources can be identified: an isotopically primitive (Sri, 0.7050; ϵNdT, 2.3 to –1.2), subduction-related source probably associated with the mid-Cretaceous continental margin; an isotopically primitive (Sri, 0.7032 to 0.7035; ϵNdT, 4.2 to 1.4), non-subduction-related source identified as the host Cache Creek terrane; and an isotopically slightly more evolved (Sri, 0.7094 to 0.7101; ϵNdT, 4.5 to –7.3), subduction-related source identified as the host Stikine terrane. Immediately east of the Teslin Tectonic Zone (TTZ), pericratonic Omineca granites (Sri, 0.7032 to 0.7076; ϵNdT, 2.0 to –5.4) do not correlate with their host terranes, but instead show marked similarities with granites immediately to the west of the TTZ suggesting that the same, or similar crustal sources extend further east in the subsurface than previously thought. In the eastern pericratonic Omineca Belt, there is a substantial jump to more evolved isotopic values (Sri, 0.7172 to 0.7354; ϵNdT, –16.6 to –21.7) for granites that extend to the most easterly exposed plutons of the cratonic Omineca Belt. These more isotopically evolved granites correlate with isotopic values for the pericratonic Yukon–Tanana and Cassiar terranes, as well as cratonic North America.

Revolutionary Russia

1918 ◽  
Vol 12 (2) ◽  
pp. 181-191
Author(s):  
Simon Litman
Keyword(s):  
North America ◽  
Self Determination ◽  
The South ◽  
The West ◽  
The Past ◽  
The North ◽  
The Earth ◽  
The Face ◽  
Historic Development

From tyrannical autocracy to a most radically socialistic régime, from an empire oppressing subjugated peoples to a country proclaiming the principle of “self-determination of nationalities”—such has been the remarkable record of Russia during the past year. These changes, which have come to many as a surprise, were to those acquainted with the ferment permeating Russian life but the logical outcome of Russia's historic development.In order to be able to interpret the trend of recent events there, events which since the overthrow of Tsarism have been moving with such bewildering rapidity, it is necessary to know what have been the forces that have shaped the life of the country. Russian evolution has come through periods of subjugation, through century long struggles for self-assertion against invaders, through many internal uprisings and through successful wars of expansion. Beginning as a small principality in the interior of a plain, Russia spread to the north and to the south, to the west and to the east until she became a world empire, in area the greatest compact country on the face of the earth, occupying 8,505,000 square miles, or larger in size than all of North America, and having a population of over 175,000,000 people.

Llandovery graptolite biostratigraphy and paleobiogeography, Cape Phillips Formation, Canadian Arctic Islands

1989 ◽  
Vol 26 (9) ◽  
pp. 1726-1746 ◽  
Author(s):  
Michael J. Melchin
Keyword(s):  
North America ◽  
Canadian Arctic ◽  
The Arctic ◽  
Canadian Cordillera ◽  
Canadian Arctic Archipelago ◽  
The South ◽  
Cape Phillips Formation ◽  
Shallow Basin

Llandovery graptolites have been collected from 11 sections in the Cape Phillips Formation of the Canadian Arctic Archipelago: Melville, Bathurst, Truro, Cornwallis, Devon, and Ellesmere islands. The Cape Phillips Formation appears to have been deposited in a distinct subbasin, here termed the Cape Phillips Basin, under deep-shelf to shallow-basin conditions intermediate in position between the Arctic Platform to the south and east and the deeper Hazen Trough to the northwest.A total of 170 graptolite species and a further 25 subspecies have been identified. Their stratigraphic distribution allows the recognition of 11 graptolite zones: the acuminatus, atavus, acinaces, cyphus, curtus, convolutus, minor, turriculatus, crispus, griestoniensis, and sakmaricus zones. The curtus Zone can be subdivided into the pectinatus and orbitus subzones. The zones can be correlated with graptolite sequences worldwide.The Canadian Arctic faunas show strong affinities with those of Siberia, China, and the northern Canadian Cordillera. It may be possible to recognize a circum-equatorial faunal province in northern North America, Siberia, and China based on the occurrence of distinctive forms including Agetograptus and "Paramonoclimacis" in the middle Llandovery and certain Cyrtograptus species (especially C. sakmaricus) in the upper Llandovery.

Silurian and Devonian base maps

1985 ◽  
Vol 309 (1138) ◽  
pp. 57-77 ◽  
Keyword(s):  
Great Britain ◽  
North America ◽  
Middle Devonian ◽  
Northern Europe ◽  
Late Devonian ◽  
The South ◽  
Early Devonian ◽  
Red Sandstone ◽  
Palaeomagnetic Data

During the Silurian and Devonian, the sequence of continental collisions that were ultimately to result in the formation of the supercontinent of Pangaea had begun. By the Early to Middle Devonian North America (Laurentia), Acadia, Great Britain, and Northern Europe (Baltica) had collided to form the ‘Old Red Sandstone’ continent (Laurussia). Palaeomagnetic data, however, indicate that the configuration of the continents that made up Laurussia did not resemble the pre-breakup, Mesozoic reassembly. Rather, Britain, Baltica, and Acadia were displaced 10—20° to the south with respect to Laurentia. New palaeomagnetic data for Laurentia and Gondwana, suggests that the ocean separating the northern and southern continents was relatively narrow during the early Devonian, and may have been nearly closed by the late Devonian.

scholarly journals MANAGEMENT OF INDIGENOUS NORTH AMERICAN DEER AT THE END OF THE 20TH CENTURY IN RELATION TO LARGE PREDATORS AND PRIMARY PRODUCTION

1999 ◽  
Vol 47 (1) ◽  
pp. 1-16 ◽  
Author(s):  
C. Daigle ◽  
M. Crête
Keyword(s):  
North America ◽  
Primary Production ◽  
Boreal Forest ◽  
Mule Deer ◽  
Current Status ◽  
The South ◽  
The West ◽  
The North ◽  
South West ◽  
Large Predators

Five deer species occupy North America: caribou (3.6 × 106individuals), moose (1.1 × 106), white-tailed deer (28.5 × 106), mule deer (5.0 × 106) and wapiti (1.1 × 106). Caribou characterise the north of the boreal forest and the tundra, whereas moose dominate in coniferous and mixed forests growing further south. White-tailed deer are typical of the deciduous forests of the east while mule deer replace them in the mountainous terrain of the west. Wapiti possess the smallest range, mostly adjacent to the prairies to the west. The two large obligate carnivores preying on deer show a reduced distribution: wolves are almost restricted to Canada, and cougar to the mule deer range. We determined the current status of each species with the help of a questionnaire mailed to all jurisdictions harbouring deer. Most reports of threatened populations concerned caribou whereas many jurisdictions declared overabundance of white-tailed deer and wapiti. Hunting was allowed for all species when they abounded in a jurisdiction. Hunters harvested annually 7.0 × 106deer on the continent, 87% being white-tailed deer. The two species that caused most conflicts with humans had the highest harvest rate: 16-17%. In terms of biomass, white-tailed deer and wapiti yielded the highest harvests, with 55 and 39 kg × km-2of range, respectively. The average standing biomass of deer in winter ranged between 28 kg × km-2in Nevada to 901 kg × km-2in Indiana. The lowest standing biomasses occurred in the boreal forest (predators), in the prairies (agriculture) and in the south-west (aridity), and the highest ones in the south-east, where only white-tailed deer is present. The current abundance of deer in North America parallels, in general, the primary production of the landscape (r2= 0.38; P < 0.0001), but predators and human activity modify this pattern.

A MIGRATION OF THE DRAGONFLY, LIBELLULA QUADRIMACULATA L.

1936 ◽  
Vol 68 (12) ◽  
pp. 283-284 ◽  
Author(s):  
R. D. Bird ◽  
Donald Denning
Keyword(s):  
North America ◽  
Maximum Temperature ◽  
Migratory Behavior ◽  
The South ◽  
The West ◽  
Thunder Storm ◽  
Residential District ◽  
Different Parts

Libellula quadrimaculata L. is a holarctic dragonfly which exhibits gregaricus and migratory behavior. “Immense swarms of this species have been recorded in different parts of Europe cn many occasions” (Tillyard) but such flights have not often been recorded in North America. On June 26 a large flight was observed by R. D. Bird at Brandon, Manitoba in a residential district at the south end of town. The location is thickly planted with Manitoba maple trees which reach a height of thirty to thirty-five feet. To the west and south are severa1 sloughs where the dragonflies might have bred but none of them are within a mile and most of them considerably farther. The day was hot and sultry with a maximum temperature of 85°. A violent thunder storm accompanied by hail passed just to the south in the evening. There was a light west breeze. The flight was first semen at 6.00 p.m.

Regional setting of Carboniferous volcanism in the Midland Valley of Scotland

1993 ◽  
Vol 84 (3-4) ◽  
pp. 209-212 ◽  
Author(s):  
B. G. J. Upton
Keyword(s):  
North America ◽  
Continental Crust ◽  
Early Carboniferous ◽  
The South ◽  
The Urals ◽  
The West ◽  
Far North ◽  
The North ◽  
South West ◽  
Block Faulting

ABSTRACTIn the early Carboniferous, the portion of continental crust that now constitutes Scotland lay within the hinterland of a large continent that extended westwards to what is now the western parts of North America, eastwards to what is now the Urals and northwards towards what is now Arctic Canada, Greenland, Scandinavia and Russia. Open ocean probably lay at between 600 and 1000 km to the south. Whereas mountainous terrane lay to the north of the Highland Boundary fault, the Scottish Midland Valley, like the Northumberland Trough further south, was a region of low relief subject to periodic marine incursions.A period of block faulting and concomitant basaltic volcanism commenced at the beginning of the Carboniferous at c. 350 Ma. This had manifestations in various regions of the British Isles from the south-west of England to the west of Ireland and as far north as the Midland Valley (Francis 1978, 1991; Upton 1982; Cameron and Stephenson 1985).

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