Erratum: Crude quantitative estimates of the original northwest–southeast dimension of the Sudbury Structure, south-central Canadian Shield

1992 ◽  
Vol 29 (4) ◽  
pp. 835-835 ◽  
Author(s):  
W. S. Shanks ◽  
W. M. Schwerdtner
Keyword(s):  
Canadian Shield ◽  
South Central ◽  
Quantitative Estimates ◽  
Sudbury Structure

Crude quantitative estimates of the original northwest–southeast dimension of the Sudbury Structure, south-central Canadian Shield

1991 ◽  
Vol 28 (10) ◽  
pp. 1677-1686 ◽  
Author(s):  
W. S. Shanks ◽  
W. M. Schwerdtner
Keyword(s):  
Finite Element Modelling ◽  
Diameter Ratio ◽  
Tectonic Deformation ◽  
Two Dimensional ◽  
Meteorite Impact ◽  
Element Modelling ◽  
South Central ◽  
Quantitative Estimates ◽  
Sudbury Structure ◽  
Circular Outline

The Sudbury Structure, central Ontario, is the remnant of a large cryptoexplosion structure whose oval map pattern (diameter ratio 2.2) differs markedly from the circular outline of many meteorite impact craters. Finite-element modelling shows that (i) the original northwest–southeast dimension could have been 2–3 times larger than at present and (ii) the vertical dimension of the Sudbury Structure was > 10 km before tectonic deformation. Although our structural analyses furnish data that govern the geometric modelling, large uncertainties remain where the state of tectonic deformation is poorly constrained. A series of two-dimensional models was made to cope with kinematic uncertainties and to assess their effect on the estimates of the geometry of the original Sudbury Structure.

scholarly journals Crustal velocity structure of the Superior and Grenville provinces of the southeastern Canadian Shield

1997 ◽  
Vol 34 (8) ◽  
pp. 1167-1184 ◽  
Author(s):  
S. Winardhi ◽  
R. F. Mereu
Keyword(s):  
Greenstone Belt ◽  
Velocity Structure ◽  
Canadian Shield ◽  
Crustal Thickening ◽  
Surface Velocity ◽  
Data Set ◽  
Tectonic Zone ◽  
Near Surface ◽  
Abitibi Greenstone Belt ◽  
Sudbury Structure

The 1992 Lithoprobe Abitibi–Grenville Seismic Refraction Experiment was conducted using four profiles across the Grenville and Superior provinces of the southeastern Canadian Shield. Delay-time analysis and tomographic inversion of the data set demonstrate significant lateral and vertical variations in crustal velocities from one terrane to another, with the largest velocity values occurring underneath the Central Gneiss and the Central Metasedimentary belts south of the Grenville Front. The Grenville Front Tectonic Zone is imaged as a southeast-dipping region of anomalous velocity gradients extending to the Moho. The velocity-anomaly maps suggest an Archean crust may extend, horizontally, 140 km beneath the northern Grenville Province. Near-surface velocity anomalies correlate well with the known geology. The most prominent of these is the Sudbury Structure, which is well mapped as a low-velocity basinal structure. The tomography images also suggest underthrusting of the Pontiac and Quetico subprovinces beneath the Abitibi Greenstone Belt. Wide-angle PmP signals, indicate that the Moho varies from a sharp discontinuity south of the Grenville Front to a rather diffuse and flat boundary under the Abitibi Greenstone Belt north of the Grenville Front. A significant crustal thinning near the Grenville Front may indicate post-Grenvillian rebound and (or) the extensional structure of the Ottawa–Bonnechere graben. Crustal thickening resulting from continental collision may explain the tomographic images showing the Moho is 4–5 km deeper south of the Grenville Front.

Empirical Prediction of Crustacean Zooplankton Biomass in Nutrient-Poor Canadian Shield Lakes

1986 ◽  
Vol 43 (4) ◽  
pp. 788-796 ◽  
Author(s):  
N. D. Yan
Keyword(s):  
Total Phosphorus ◽  
Trophic State ◽  
Zooplankton Biomass ◽  
Canadian Shield ◽  
Phosphorus Concentration ◽  
Trophic State Index ◽  
Entire Study ◽  
South Central ◽  
Wide Range ◽  
Shield Lakes

A comparison of the predictive power of nine existing empirical zooplankton biomass models indicated that lake water phosphorus concentration may be a better predictor of zooplankton biomass in Canadian Shield lakes than phytoplankton biomass, chlorophyll a, midsummer epilimnetic temperature, mean surface water temperature, mean depth, and Carlson's trophic state index. To develop models specifically applicable to nutrient-poor Canadian Shield lakes, a variety of morphometric, chemical, and planktonic parameters were assessed for three consecutive years from 16 Canadian Shield lakes in south-central Ontario. Total nitrogen was the best univariate predictor of zooplankton biomass for data averaged over single ice-free seasons, but total phosphorus was the best predictor when data were averaged over the entire study period. Consideration of pH and maximum depth improved certain models. Total phosphorus is clearly a good predictor of (long-term) average zooplankton biomass in nutrient-poor lakes as it is in lakes exhibiting a wide range in trophic state.

An introduction to the Dorset special issue: transforming understanding of factors that regulate aquatic ecosystems on the southern Canadian Shield

2008 ◽  
Vol 65 (5) ◽  
pp. 781-785 ◽  
Author(s):  
Norman D Yan ◽  
Andrew M Paterson ◽  
Keith M Somers ◽  
Wolfgang A Scheider
Keyword(s):  
El Niño ◽  
Aquatic Ecosystems ◽  
Environmental Science ◽  
Multiple Stressors ◽  
El Nino ◽  
Canadian Shield ◽  
Interactive Effects ◽  
Special Issue ◽  
Management Interventions ◽  
South Central

This special issue demonstrates that aquatic ecosystems on the south-central Canadian Shield have changed in many ways over the last three decades. El Niño cycles have synchronized multilake dynamics in lake-water chemistry and in several components of the aquatic biota. Overlain on this cyclic regional pattern, phosphorus, sulphate, and calcium levels have all declined, whereas alkalinity has not yet risen in the most acid-sensitive study lakes, despite large reductions in SO2 emissions. Further, novel and unanticipated stressors have appeared, including nonindigenous predator introductions, Ca decline, salinity increase, and autumn spikes in metals following El Niño induced droughts. The resident biota are clearly responding not only to the familiar historical phosphorus and acid stressors, but also to the interactive effects of changes in multiple stressors in a warming environment. Lakes are best managed with an understanding of dominant limnological trends, their causes, and their responses to past management interventions. The research conducted at the Dorset Environmental Science Centre indicates “progress but no cigar” on acid rain, proof of climate variability as a direct and indirect regulator of south-central Shield ecosystems, and the emergence of novel stressors, the effects of which we cannot yet fully predict.

Aggregation in Littoral Amphipod Populations: Transformation Controversies Revisited

1987 ◽  
Vol 44 (8) ◽  
pp. 1510-1515 ◽  
Author(s):  
R. L. France
Keyword(s):  
Literature Review ◽  
Power Law ◽  
Habitat Type ◽  
Canadian Shield ◽  
Power Relationship ◽  
Square Root ◽  
South Central ◽  
Root Transformation ◽  
Fourth Root ◽  
Shield Lakes

Spatial variability in amphipod (Hyalella azteca) density was examined in 17 Canadian Shield Lakes in south-central Ontario. Aggregation was measured by the exponent of the power relationship between density and variance. The average b index was 1.45, although this value varied depending on lake and habitat type. Whereas this should indicate the use of a fourth-root transformation, neither this nor the logarithmic transformation was as effective as the square-root in stabilizing variance. A literature review suggests that if a universal transformation is sought for benthos data, it should not be the commonly used log transformation. The observation that the square-root transformation seemed to work better on average than the fourth-root transformation, even in the region suggested by theory for the latter, suggests that complications may arise in the uncritical use of Taylor's Power Law.

Paleomagnetism of the Michael Gabbro and Possible Evidence of the Rotation of Makkovik Subprovince

1972 ◽  
Vol 9 (10) ◽  
pp. 1287-1296 ◽  
Author(s):  
W. F. Fahrig ◽  
A. Larochelle
Keyword(s):  
North America ◽  
Remanent Magnetization ◽  
Pole Position ◽  
Canadian Shield ◽  
Main Body ◽  
Central Coast ◽  
Tectonic Event ◽  
South Central ◽  
Paleomagnetic Pole ◽  
Paleomagnetic Study

The Michael gabbro forms a belt of thick, predominantly southerly-dipping sheets which extends 200 km inland from the south-central coast of Labrador. The intrusions lie largely within the Makkovik subprovince, have a radioisotopic age of 1500 m.y., and are reversely magnetized with a paleomagnetic pole position of 163 °E, 10 °N. The paleomagnetic results indicate that most of the rocks internal to this belt have not been deformed since the intrusions acquired a stable remanent magnetization, presumably at the time of cooling 1500 m.y. ago. However, the Michael pole position differs significantly from those of rocks of similar age elsewhere in North America. This suggests rotation of the block containing the Michael intrusions relative to these other rocks. The Aillik dikes which also lie within the Makkovik sub-province have a radioisotopic age of about 1100 m.y. and a pole position consistent with that of rocks of similar age elsewhere in the Canadian Shield. The postulated Michael rotation must then have taken place between 1500 and 1100 m.y. ago.The rock at two of the most southerly sites sampled for paleomagnetic study proved to be magnetically unstable and the rock at a third such site, though stably magnetized has a magnetization significantly different from the main body of Michael gabbro intrusions. These three sites may indicate a post-consolidation thermal and tectonic event and their position may help define the Grenville Front in this region.

scholarly journals Subsurface Flow in a Shallow Soil Canadian Shield Watershed

1992 ◽  
Vol 23 (4) ◽  
pp. 209-226 ◽  
Author(s):  
Adrian V. E. Renzetti ◽  
Colin H. Taylor ◽  
James M. Buttle
Keyword(s):  
Subsurface Flow ◽  
Surface Flow ◽  
Canadian Shield ◽  
Peak Discharge ◽  
Storm Events ◽  
South Central ◽  
Flow Mechanisms ◽  
Recession Rates ◽  
Bedrock Surface ◽  
Shallow Soils

Past studies in Canadian Shield headwater catchments have identified the importance of subsurface flow mechanisms in generating storm runoff. Recent work in the Muskoka-Haliburton region of south-central Ontario has suggested that subsurface flow within hillslopes with shallow soils occurs primarily along impermeable bedrock surfaces. Two trenches were dug on the side slope of a small headwater catchment and instrumented to measure flows at different levels in the soil. Results show that flow over the bedrock surface constitutes the largest component of hillslope discharge during fall rain storms. Peak discharge and recession rates for bedrock surface flow hydrographs were synchronous with channel discharge. Calculations show that this component of hillslope flow could account for the majority of peak discharge during storm events.

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