Paleomagnetism and U–Pb geochronology of the 2.17 Ga Biscotasing dyke swarm, Ontario, Canada: evidence for vertical-axis crustal rotation across the Kapuskasing Zone

2004 ◽  
Vol 41 (3) ◽  
pp. 255-269 ◽  
Author(s):  
Henry C Halls ◽  
Donald W Davis
Keyword(s):  
Vertical Axis ◽  
Paleomagnetic Data ◽  
Dyke Swarm ◽  
Superior Province ◽  
Hudson Bay ◽  
Short Period ◽  
Western Half ◽  
Eastern Half

U–Pb dates on baddeleyite yield ages of 2167.8 ± 2.2 and 2171.6 ± 1.2 Ma on two northeast-trending dykes west of the Kapuskasing Zone in Ontario, Canada. These ages identify the dykes as belonging to the Biscotasing dyke swarm east of the Kapuskasing Zone, which was previously dated at 2166.7 ± 1.4 Ma by U–Pb on baddeleyite and zircon. The new dates show that the Biscotasing swarm was emplaced over an area of at least 300 000 km2, much larger than hitherto suspected, and in a geologically short period of time of about 5 million years. A comparison of paleomagnetic data from Biscotasing and 2.45 Ga Matachewan dykes on either side of the Kapuskasing Zone suggests that the western half of the Superior Province has rotated about 10°–20° counterclockwise relative to the eastern half across the Kapuskasing Zone. This movement may have been accompanied by rifting farther north which ultimately led to the Paleoproterozoic embayment, underlying Hudson Bay, that gives the Superior Province its characteristic butterfly-shaped outline.

Paleomagnetism, U–Pb geochronology, and geochemistry of Lac Esprit and other dyke swarms, James Bay area, Quebec, and implications for Paleoproterozoic deformation of the Superior Province

2007 ◽  
Vol 44 (5) ◽  
pp. 643-664 ◽  
Author(s):  
Kenneth L Buchan ◽  
Jean Goutier ◽  
Michael A Hamilton ◽  
Richard E Ernst ◽  
William A Matthews
Keyword(s):  
Vertical Axis ◽  
Geological Mapping ◽  
Superior Province ◽  
Hudson Bay ◽  
James Bay ◽  
Common Reference ◽  
Bay Area ◽  
The North ◽  
The Difference ◽  
Dyke Swarms

An extensive set of north- to northwest-trending diabase dykes, termed the Lac Esprit swarm, is identified in the Superior Province east of James Bay based on geological mapping and a distinctive paleomagnetic pole (61.7°N, 169.1°E, dm = 7.7°, dp = 5.5°). The Lac Esprit swarm yields a U–Pb baddeleyite age of 2069 ± 1 Ma similar to that of the 2076+5–4 Ma Fort Frances swarm of the western Superior Province. Their paleomagnetic declinations differ by 23° ± 12° after correction to a common reference locality. The difference is likely due mainly to counterclockwise rotation about a vertical axis of the Fort Frances area relative to the Lac Esprit area. Differential rotation of 10°–20° has been proposed more locally across the Kapuskasing Structural Zone separating the eastern and western Superior Province in earlier paleomagnetic studies of ca. 2450 Ma Matachewan and 2170 Ma Biscotasing dyke swarms. Thus, relative rotation may have involved the entire eastern and western Superior Province, perhaps in response to collisional events associated with the Trans-Hudson Orogen to the north or the Penokean orogen to the south, or in response to rifting beneath Hudson Bay. Other dykes in the study area are interpreted from a combination of paleomagnetism, trend, and geochemistry to belong to the Senneterre, Matachewan, and Mistassini swarms. The 2216 Ma Senneterre dykes form part of a giant swarm that fans across the eastern Superior Province. Paleomagnetic directions and geometry of this swarm rule out substantial block rotations within the eastern Superior Province since dyke emplacement.

scholarly journals A 2169 Ma U–Pb baddeleyite age for the Otish Gabbro, Quebec: implications for correlation of Proterozoic magmatic events and sedimentary sequences in the eastern Superior Province

2016 ◽  
Vol 53 (2) ◽  
pp. 119-128 ◽  
Author(s):  
Michael A. Hamilton ◽  
Kenneth L. Buchan
Keyword(s):  
East Coast ◽  
Sedimentary Rocks ◽  
Uranium Mineralization ◽  
Dyke Swarm ◽  
Superior Province ◽  
Hudson Bay ◽  
Sedimentary Sequences ◽  
The North ◽  
Paleomagnetic Study ◽  
Fluid Event

Otish Gabbro sills intrude sedimentary rocks in the Otish Basin of the southeastern Superior Province. Here, deposition of Otish Supergroup sediments had previously been thought to be older than K–Ar and Sm–Nd ages of ca. 1750–1710 Ma for Otish Gabbro sills, and younger than ca. 2515–2500 Ma U–Pb ages of underlying Mistassini dykes. However, a much older U–Pb baddeleyite age of 2169.0 ± 1.4 Ma is presented here for an Otish sill, indicating that they are coeval with, and likely genetically related to, the giant 2172–2167 Ma Biscotasing dyke swarm to the southwest and (or) the Cramolet sills and Payne River dykes to the north. The new date also indicates that the age of the Otish Supergroup falls between ca. 2515 Ma and ca. 2169 Ma, only a little different from the ca. 2450–2217 Ma bracket for the Huronian Supergroup of the Southern Province, and is consistent with both supergroups spanning the oxy-atmo inversion. The Otish Supergroup could also be coeval with the Sakami Formation to the north, but is likely older than the Richmond Gulf Group on the east coast of Hudson Bay. Early paleomagnetic study of Otish sills yielded a remanence ∼20° from that expected for Biscotasing-aged intrusions. This may indicate that too few distinct sills were studied to average out paleosecular variation, that demagnetization techniques failed to fully remove unstable magnetization components, or that the remanence is a stable secondary overprint, perhaps acquired during a fluid event related to uranium mineralization at ca. 1720 Ma.

scholarly journals Productivity of Ospreys, Pandion haliaetus, Affected by Water Levels Near Loon Lake, Saskatchewan, 1975-2002

2010 ◽  
Vol 124 (3) ◽  
pp. 219
Author(s):  
C. Stuart Houston ◽  
Frank Scott ◽  
Rob B. Tether
Keyword(s):  
Breeding Success ◽  
Water Levels ◽  
Lake Levels ◽  
The West ◽  
Canadian Data ◽  
Human Use ◽  
The Town ◽  
Western Half ◽  
Eastern Half

Between 1975 and 2002, diminished breeding success of Ospreys was associated with drought and falling lake levels in the western half of our study area near the town of Loon Lake, west-central Saskatchewan. Only 46% of nest attempts were successful in the west compared to 72% in the east, producing 0.88 young per accessible nest in the west and 1.42 in the east. Breeding success was greater in the eastern half, where water levels were stable, in spite of increased human use of the resort lakes there. Our unique long-term Canadian data base results support Ogden's 1977 prediction that Osprey productivity may decrease when water levels drop and fish populations are reduced.

Farmers and the Market in Antebellum America: A View from the Georgia Upcountry

1987 ◽  
Vol 47 (3) ◽  
pp. 627-647 ◽  
Author(s):  
David F. Weiman
Keyword(s):  
Local Development ◽  
Household Wealth ◽  
Capital Gains ◽  
Farm Households ◽  
Market Development ◽  
Antebellum America ◽  
Market Production ◽  
Lower South ◽  
Western Half ◽  
Eastern Half

The Upcountry of the Lower South was located on the periphery of the antebellum cotton economy, but some of its subregions were integrated into the market system in the 1850s. An analysis of sample counties in the Georgia Upcountry demonstrates that the spread of market production into the western half of the region depended on local development which created opportunities for diversified market production and increased household wealth through capital gains on improvements. The absence of market development in the eastern half of the region, in contrast, limited the wealth of farm households, reinforcing their economic isolation.

Contribution a l'etude geomorphologique du nord-est du Bresil

1961 ◽  
Vol S7-III (5) ◽  
pp. 492-500
Author(s):  
Andre R. Meunier
Keyword(s):  
Rio Grande ◽  
The North ◽  
Littoral Region ◽  
Morphologic Characteristics ◽  
Western Half ◽  
Eastern Half ◽  
Semi Arid

Abstract A region of 40,000 km <sup>2</sup> in the States of Pernambuco, Paraiba, and Rio Grande do Norte in northeastern Brasil, drained to the north by the Piranhas river and to the east by the Paraiba river, exhibits a series of Cenozoic erosion levels showing the morphologic characteristics of littoral and interior zones. Rocks of the region are a poorly-known Precambrian complex attributed to the Algonkian. In the semi-arid western half of the region, west of the meridian of Campina Grande, are the Chapadas, Soledad, and Patos levels, respectively at 830-650, 600-550, and 300-250 m elevation. In the eastern half of the littoral region are the Borborema and Umbuzeiro surfaces, the probably Pliocene Tabuleiros gently sloping from 200 to 20 m at the seacoast, and the Itabaiana surface at about 90 m. These features reflect successive border flexures of the Brazilian shield, and progressive accentuation of an enormous fold at depth.

Paleomagnetism and U-Pb geochronology of diabase dyke swarms of Minto block, Superior Province, Quebec, Canada

1998 ◽  
Vol 35 (9) ◽  
pp. 1054-1069 ◽  
Author(s):  
Kenneth L Buchan ◽  
James K Mortensen ◽  
Kenneth D Card ◽  
John A Percival
Keyword(s):  
Collaborative Study ◽  
Sedimentary Rocks ◽  
Dyke Swarm ◽  
Superior Province ◽  
Mafic Dyke ◽  
Magnetization Direction ◽  
Virtual Geomagnetic Pole ◽  
Southern Province ◽  
Geomagnetic Pole ◽  
Dyke Swarms

In the first collaborative study of paleomagnetism and precise U-Pb geochronology in the Minto block of the Superior Province, mafic dyke swarms with three widely divergent paleomagnetic signatures and isotopic ages have been identified. The 2505 ± 2 Ma Ptarmigan dykes trend north to northeast and have a virtual geomagnetic pole at 42°S, 220°E, similar to that of 2473-2446 Ma Matachewan dykes of the southern Superior Province. The ca. 2230 Ma Maguire dykes trend west to northwest and yield a paleopole at 9°S, 267°E, similar to those for 2216+8-4 Ma Senneterre dykes and 2217-2210 Ma Nipissing sills of the southern Superior and Southern provinces, respectively. The 2209 ± 1 Ma Klotz dykes trend west-northwest, but do not carry a consistent magnetization direction. Finally, 1998 ± 2 Ma Minto dykes of west-northwest to northwest trend, identical in age to the 1998 Ma ± 2 Ma Purtuniq ophiolite of the Cape Smith Belt, have a paleopole at 38°N, 174°E. The similarity of paleopoles for the ca. 2.23-2.21 Ga Maguire dykes of the Minto block, Senneterre dykes of the southern Superior, and Nipissing sills of the Southern Province demonstrates that these regions were in their present relative latitudes and orientations at that time. Likewise, the similarity of the Ptarmigan virtual geomagnetic pole and the Matachewan paleopole suggests little relative latitudinal movement or rotation of the two regions since ca. 2.5 Ga. The Maguire, Senneterre, and Klotz dykes form a roughly radiating pattern and may represent one quadrant of a giant radiating dyke swarm centred southeast of Ungava Bay, whose focus marks the location of a mantle plume responsible for ca. 2.22 Ga breakup along the eastern margin of the Superior Province. If so, the coeval Nipissing sills that intrude sedimentary rocks of the Huronian Supergroup of the Southern Province may have been fed laterally by Senneterre dykes from the Ungava plume centre.

scholarly journals Hush-hushing the whole matter: The UNHCR, Australia, and West Papuan Refugees

Refuge ◽  
2006 ◽  
pp. 69-80
Author(s):  
Klaus Neumann
Keyword(s):  
Asylum Seekers ◽  
New Guinea ◽  
Historical Case Study ◽  
Australian Government ◽  
Historical Case ◽  
High Commissioner ◽  
The Relationship ◽  
Western Half ◽  
Eastern Half

Between 1962 and 1973, thousands of refugees crossed from the Indonesian-controlled western half of the island of New Guinea into the Australian-controlled eastern half. The United Nations High Commissioner for Refugees (UNHCR) refrained from becoming involved in the issue, and from publicly criticizing the Australian government over its response to West Papuan asylum seekers. In return, the Australian government committed itself to keeping the High Commissioner informed about developments in New Guinea on the understanding that it would provide information on a strictly confidential basis. The article explores the High Commissioner’s possible motives for effectively condoning Australia’s refugee policies in Papua and New Guinea. It demonstrates the relevance of this historical case study for our understanding of current Australian policies and for evaluating the relationship between the UNHCR and governments.

scholarly journals The Flow of Water Past the Seven Stones Lightvessel

1934 ◽  
Vol 19 (2) ◽  
pp. 921-930 ◽  
Author(s):  
J. N. Carruthers
Keyword(s):  
Wind Speed ◽  
Residual Current ◽  
The State ◽  
Entire Period ◽  
Northern Half ◽  
The Individual ◽  
The Right ◽  
Western Half ◽  
Eastern Half

A brief reference to the state of opinion concerning the water movements off S.W. England is made. Then a series of Drift Indicator records relating to 28 days of observation at 6 fathoms depth from the Seven Stones Lightvessel is presented and discussed. An overall flow of water towards the S.E. quadrant and of speed approaching 2 miles per day characterised the entire period. The residual current as worked out for the individual records, displayed considerable variation in speed and direction—setting as frequently towards the northern half of the compass as towards the southern, but more frequently towards the eastern half than towards the western half. There were pronounced changes in the wind speed and direction, and it appears as though the wind can drive the water at 6 fathoms depth towards a point to the right of its own direction, no matter from which of the four quadrants it blows.

scholarly journals Evaluation of Modeled Precipitation in Oceanic Extratropical Cyclones Using IMERG

2019 ◽  
Vol 33 (1) ◽  
pp. 95-113 ◽  
Author(s):  
Catherine M. Naud ◽  
Jeyavinoth Jeyaratnam ◽  
James F. Booth ◽  
Ming Zhao ◽  
Andrew Gettelman
Keyword(s):  
Climate Models ◽  
Extratropical Cyclone ◽  
High Temporal Resolution ◽  
Extratropical Cyclones ◽  
Precipitation Frequency ◽  
Precipitation Characteristics ◽  
Satellite Retrievals ◽  
Precipitation Changes ◽  
Western Half ◽  
Eastern Half

ABSTRACT Using a high-spatial- and high-temporal-resolution precipitation dataset, Integrated Multi-satellite Retrievals for GPM (IMERG), extratropical cyclone precipitation is evaluated in two reanalyses and two climate models. Based on cyclone-centered composites, all four models overestimate precipitation in the western subsiding and dry side of the cyclones, and underestimate the precipitation in the eastern ascending and moist side. By decomposing the composites into frequency of occurrence and intensity (mean precipitation rate when precipitating), the analysis reveals a tendency for all four models to overestimate frequency and underestimate intensity, with the former issue dominating in the western half and the latter in the eastern half of the cyclones. Differences in frequency are strongly dependent on cyclone environmental moisture, while the differences in intensity are strongly impacted by the strength of ascent within the cyclone. There are some uncertainties associated with the observations: IMERG might underreport frozen precipitation and possibly exaggerate rates in vigorously ascending regions. Nevertheless, the analysis suggests that all models produce extratropical cyclone precipitation too often and too lightly. These biases have consequences when evaluating the changes in precipitation characteristics with changes in cyclone properties: the models disagree on the magnitude of the change in precipitation intensity with a change in environmental moisture and in precipitation frequency with a change in cyclone strength. This complicates accurate predictions of precipitation changes in a changing climate.

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