ERRATUM: AN ESTIMATE OF THE COMPOSITION OF PART OF THE CANADIAN SHIELD IN NORTHWESTERN ONTARIO

1967 ◽  
Vol 4 (6) ◽  
pp. 1269-1269
Author(s):  
G. A. Reilly ◽  
D. M. Shaw
Keyword(s):  
Canadian Shield ◽  
Northwestern Ontario

Rare earth distribution in Archean granitoid plutons of the Wabigoon volcanic–plutonic belt, northwestern Ontario

1979 ◽  
Vol 16 (2) ◽  
pp. 270-289 ◽  
Author(s):  
Dieter Birk ◽  
Tapio Koljonen ◽  
R. J. Rosenberg
Keyword(s):  
Rare Earth ◽  
Steep Slope ◽  
Canadian Shield ◽  
Secular Change ◽  
Source Modeling ◽  
Northwestern Ontario ◽  
History Of ◽  
Plutonic Belt ◽  
High Concentrations ◽  
Ree Patterns

Rare earths (La to Lu, Y) are investigated for five Archean granitoid stocks of Kenoran age that intrude the Wabigoon volcanic–plutonic belt. Homogeneous granodiorites are characterized by low total rare earth concentrations (ΣREE), with chondrite-normalized REE patterns that show steep negative slopes, no Eu anomalies, and enrichment of Lu. A hypabyssal porphyry of possible volcanic affiliation displays similar REE patterns, but is more depleted in heavy REE. Zone plutons yield patterns of steep slope, no Eu anomalies, with or without Lu enrichment. REE concentrations decrease from monzodioritic margins, to granodioritic cores, to aplitic apophyses.These plutons carry REE concentrations similar to the Canadian Shield average, but notably lower than some published averages for granitoids. No secular change is evident for the Archean interval.ΣREE decreases during differentiation with no appreciable fractionation of heavy over light REE, until the end stages. Late differentiates suffer depletion in heavy REE by hornblende fractionation. Lu enrichment correlates with deuteric metasomatism, as evidenced by microcline megacrysts. Eu anomalies are absent because fractionation of divalent Eu is prevented by high concentrations of Sr and Ba.Quantitative source modeling should consider the complete magma history of emplacement, crystallization, and deuteric metasomatism.

Orthoquartzite pebbles in Archean conglomerate, North Spirit Lake, northwestern Ontario

1977 ◽  
Vol 14 (9) ◽  
pp. 1980-1990 ◽  
Author(s):  
J. A. Donaldson ◽  
Richard W. Ojakangas
Keyword(s):  
Greenstone Belt ◽  
Sedimentary Rocks ◽  
Canadian Shield ◽  
Superior Province ◽  
Lake Area ◽  
Definite Evidence ◽  
The North ◽  
Northwestern Ontario ◽  
Form Part ◽  
Quartz Grains

An Archean conglomerate in the North Spirit Lake area of northwestern Ontario contains rare orthoquartzite pebbles. Detailed study of these pebbles shows that mineralogically they are very mature, consisting of as much as 99.8 percent quartz and a heavy mineral suite of zircon, tourmaline, and apatite. Textures are typically bimodal, characterized by rounded sand-sized quartz grains set in a 'matrix-cement' of thoroughly recrystallized finer quartz grains. These orthoquartzite pebbles provide the first definite evidence for local tectonic stability of the Canadian Shield before deposition of the immature sedimentary rocks that form part of an Archean (>2.6 Ga) greenstone belt of the Superior Province.

Preliminary Chemical Characterization of Waters in the Experimental Lakes Area, Northwestern Ontario

1971 ◽  
Vol 28 (2) ◽  
pp. 171-187 ◽  
Author(s):  
F. A. J. Armstrong ◽  
D. W. Schindler
Keyword(s):  
Chemical Characterization ◽  
Specific Conductance ◽  
Canadian Shield ◽  
Nitrogen And Phosphorus ◽  
Experimental Lakes Area ◽  
Mean Values ◽  
Dissolved Phosphorus ◽  
Dissolved Nitrogen ◽  
Total Dissolved Nitrogen ◽  
Northwestern Ontario

Water analyses in 1968 and 1969 from 40 small lakes within a small area of the Canadian Shield in northwestern Ontario gave mean values for Ca, Na, Mg, and K of 1.6, 0.9, 0.9, and 0.4 mg/liter with Ca > Na > Mg > K on a molar basis. HCO3, SO4, and Cl (on a smaller number of samples) were 4.1, 3.0, and 1.4 mg/liter. Total CO2 was variable in the range 0.3–12.0 mg/liter. Specific conductance was in the range 10–35 μmho/cm at 25 C and pH 5.4–7.5. Color was < 5–150 Hazen units, and plant pigments (as chlorophyll a) < 1–21 μg/liter. Total dissolved nitrogen was in the range 110–300 mg N/liter and total dissolved phosphorus 3–20 μg P/liter. NO3-N and PO4-P were often undetectable in summer, and reached winter maxima around 100 and 10 μg/liter.Total dissolved nitrogen and phosphorus contents of five lakes were computed at the beginning and end of periods of several weeks during summer stagnation. Changes were negligibly small in three of the deeper lakes, but the two shallowest showed increases of 0.22 and 0.62 g N/m2 and 0.03 and 0.13 g P/m2. Analyses of precipitation and stream waters were used, with stream flow rates, to calculate input and output of nutrients from four of these lakes during the same periods. Retention of nutrients had occurred in all, and it was concluded that in the two deeper lakes nutrients had been lost to the sediments, whereas in the two shallower ones the increases in dissolved nutrients found were derived from the sediments.Analyses of 33 other Canadian Shield lake areas and of 13 other dilute lakes in other regions are tabulated. Comparison with the Experimental Lakes Area (ELA) lakes shows that the latter are more dilute than any in the Shield area except for some in the Northwest Territories, and much more dilute than any others in the world except for some alpine lakes in California.

Pelagic distribution of lake trout (Salvelinus namaycush) in small Canadian Shield lakes with respect to temperature, dissolved oxygen, and light

1998 ◽  
Vol 55 (1) ◽  
pp. 170-179 ◽  
Author(s):  
Todd J Sellers ◽  
Brian R Parker ◽  
David W Schindler ◽  
William M Tonn
Keyword(s):  
Light Intensity ◽  
Dissolved Oxygen ◽  
Lake Trout ◽  
Salvelinus Namaycush ◽  
Canadian Shield ◽  
Small Lakes ◽  
Experimental Lakes Area ◽  
Northwestern Ontario ◽  
Oxygenated Water ◽  
Shield Lakes

The distribution of lake trout (Salvelinus namaycush) with respect to water temperature, dissolved oxygen, and light intensity was surveyed in three small Canadian Shield lakes at the Experimental Lakes Area, northwestern Ontario. Based on hydroacoustic and gillnet surveys, there was considerable variation among lakes in temperatures occupied by lake trout during the summer. During the day, lake trout were concentrated at 4-8°C in Lake 375, broadly distributed from 6 to 15°C in Lake 442, and concentrated in the epilimnion at 19°C in Lake 468. At night, lake trout in all lakes occupied epilimnetic waters at 19-20°C. Lake trout inhabited highly oxygenated water, with 75-90% of fish at >6 mg dissolved oxygen ·L-1 throughout the spring and summer in all three lakes. Light intensity did not affect lake trout distribution in Lake 468 but may have contributed to lake trout daytime descent into cool waters in Lakes 375 and 442. We suggest that previously assumed niche boundaries of lake trout do not adequately describe critical habitat for the species in small lakes, the same lakes that are likely most sensitive to erosion of such habitat.

Aquatic acetylene-reduction techniques: solutions to several problems

1976 ◽  
Vol 22 (1) ◽  
pp. 43-51 ◽  
Author(s):  
R. J. Flett ◽  
R. D. Hamilton ◽  
N. E. R. Campbell
Keyword(s):  
Nitrogen Fixation ◽  
Depth Profile ◽  
Acetylene Reduction ◽  
Canadian Shield ◽  
Experimental Lakes Area ◽  
Reduction Techniques ◽  
Northwestern Ontario ◽  
Refined Technique

Previous methods of performing aquatic acetylene-reduction assays are described and several problems associated with them are discussed. A refinement of these older techniques is introduced and problems that it overcomes are also discussed. A depth profile of nitrogen fixation (C2H4 production), obtained by the refined technique, is shown for a fertilized Canadian Shield lake in the Experimental Lakes Area of northwestern Ontario.

Sensitivity of Estimates of Seasonal Phytoplankton Photosynthesis to Sampling Frequency

1994 ◽  
Vol 51 (12) ◽  
pp. 2734-2738 ◽  
Author(s):  
E. U. Schindler ◽  
E. R. DeBruyn ◽  
E. J. Fee ◽  
J. A. Shearer
Keyword(s):  
Thermal Stratification ◽  
Sampling Frequency ◽  
Canadian Shield ◽  
Data Sets ◽  
Time Intervals ◽  
Rainfall Events ◽  
Northwestern Ontario ◽  
Regular Time ◽  
Sampling Intervals ◽  
Phytoplankton Photosynthesis

Phytoplankton photosynthesis was monitored once or twice weekly in an oligotrophic Canadian Shield lake in northwestern Ontario during the ice-free season for 6 yr. These data sets were subsampled in various ways to determine how the precision of estimates of ice-free season phytoplankton photosynthesis was affected by sampling frequency. Deviations were as large as 20% if a measurement was not taken before thermal stratification was established in the spring, or if samples were taken at monthly intervals during the ice-free season. Shorter sampling intervals (1, 2, and 3 wk were tested) all resulted in deviations of about 10%. Taking samples irregularly (every day for the 3 d subsequent to rainfall events ≥ 5 mm) instead of at regular time intervals did not reduce deviations.

Copper content of Canadian shield rocks, red Lake-lansdowne house area, northwestern Ontario

1966 ◽  
Author(s):  
R F Emslie ◽  
R H C Holman
Keyword(s):  
Copper Content ◽  
Canadian Shield ◽  
Red Lake ◽  
Northwestern Ontario ◽  
House Area

scholarly journals AN ESTIMATE OF THE COMPOSITION OF PART OF THE CANADIAN SHIELD IN NORTHWESTERN ONTARIO

1967 ◽  
Vol 4 (4) ◽  
pp. 725-739 ◽  
Author(s):  
G. A. Reilly ◽  
D. M. Shaw
Keyword(s):  
Trace Elements ◽  
Significant Variation ◽  
Major Element ◽  
Canadian Shield ◽  
Element Analysis ◽  
Red Lake ◽  
Rock Types ◽  
Northwestern Ontario ◽  
House Area ◽  
Composite Samples

An attempt has been made to estimate the abundance of trace and major constituents in the Precambrian surficial rocks of a large part (43 000 square miles) of the Red Lake–Lansdowne House area in northwestern Ontario. One-hundred and two composite samples were made to represent eight rock types in seven adjacent map-areas of equal size. Major element analysis was carried out on eight composite samples representing rock types for the whole area. Analysis of variance techniques have detected significant regional variations of Cr, Mn, Sr, and Ba. Significant variation exists between rock types for all trace elements analyzed except Cu.

Trench and slope basin deposits in an Archean metasedimentary belt, Superior Province, Canadian Shield

1992 ◽  
Vol 29 (12) ◽  
pp. 2551-2557 ◽  
Author(s):  
Philip Fralick ◽  
Jinhua Wu ◽  
Howard R. Williams
Keyword(s):  
Shallow Water ◽  
Canadian Shield ◽  
Complex Medium ◽  
Superior Province ◽  
Accretionary Complex ◽  
Forearc Basin ◽  
Northwestern Ontario ◽  
Depositional Systems

The identification of a late Archean arc–trench assemblage in northwestern Ontario provides the opportunity to compare depositional systems developed in a Precambrian convergent setting with Cenozoic examples. Two types of sedimentary associations exist in the accretionary complex. Medium- to thick-bedded Bouma A, AB, and ABC felsic turbidites dominate the belt. These are primarily organized into unstructured sequences and reflect deposition in a ramp-like environment with multiple feed points supplying sediment from a forearc basin. Mafic turbidites with possible shallow water reworked intervals form isolated pods within the metasedimentary belt. Erosion of upthrust blocks of sedimentary strata containing ultramafic masses supplied this sediment to elevated slope basins. These types of depositional systems are similar in many respects to those developed in Cenozoic and Holocene arc–trench settings.

Geochronology of orthogneiss adjacent to the Archean Lake of the Woods greenstone belt, northwestern Ontario: a possible basement complex

1981 ◽  
Vol 18 (1) ◽  
pp. 94-102 ◽  
Author(s):  
G. S. Clark ◽  
R. Bald ◽  
L. D. Ayres
Keyword(s):  
Greenstone Belt ◽  
Canadian Shield ◽  
Amphibolite Facies ◽  
Isotopic Age ◽  
Basement Complex ◽  
Degree Of Deformation ◽  
Lake Of The Woods ◽  
The North ◽  
Northwestern Ontario

Deformed and recrystallized, amphibolite facies, trondhjemitic to granodioritic orthogneiss along the north margin of the Archean Lake of the Woods greenstone belt has an Rb–Sr isochron age of 2950 ± 150 Ma and an initial 87Sr/86Sr ratio of 0.7028 ± 0.0014. Preserved primary textures and complex internal intrusive relationships document the original plutonic nature of the orthogneiss. Based on isotopic age and degree of deformation and recrystallization, the orthogneiss is interpreted to be basement to the adjacent metavolcanic sequence of the greenstone belt. The contact between the orthogneiss and greenstone belt is the locus of deformation, but may be an unconformity. It is also the boundary between the English River subprovince on the north and the Wabigoon subprovince on the south.Similar orthogneiss ranging in age from 2800 to 3800 Ma is widespread in the Canadian Shield. It is basement to the 2650–2750 Ma Archean volcanism, at least in some areas, but is not necessarily basement to the older (2800–3000 Ma) volcanism. The orthogneisses are remnants of a once much more extensive sialic terrain, but the contemporaneity and extent of this sialic terrain are uncertain.

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