U-Pb age and genetic significance of heterogeneous zircon populations in rocks from the Favourable Lake area, Northwestern Ontario

1984 ◽  
Vol 88 (1-2) ◽  
pp. 86-101 ◽  
Author(s):  
F. Corfu ◽  
L. D. Ayres
Keyword(s):  
Lake Area ◽  
Northwestern Ontario ◽  
Genetic Significance

Effects of Experimental and Cultural Lake Acidification on Littoral Benthic Macroinvertebrate Assemblages

1994 ◽  
Vol 51 (5) ◽  
pp. 1147-1161 ◽  
Author(s):  
Malcolm Stephenson ◽  
Gregory Mierle ◽  
Ronald A. Reid ◽  
Gerald L. Mackie
Keyword(s):  
Correlation Matrix ◽  
Environmental Variables ◽  
Benthic Macroinvertebrate ◽  
Lake Area ◽  
Experimental Lakes Area ◽  
Simple Method ◽  
Northwestern Ontario ◽  
Kendall’S Τ ◽  
Dimension 2 ◽  
Sweep Net

A simple method for the assessment of littoral benthic macroinvertebrate (BMI) assemblages in lakes was developed at the Experimental Lakes Area (ELA) in northwestern Ontario and applied to 64 lakes in central Ontario. The presence (1) or absence (0) of BMI taxa was established at five sites on each lake, using a kick-and-sweep net technique. Summing presence/absence scores across sites ranked the importance of each taxon in each lake on a scale of 0 to 5. Relationships between the BMI assemblages were assessed using nonmetric multidimensional scaling (NMDS), based upon the Kendall's τ correlation matrix. Correlations between NMDS dimension 1 and 2 scores and environmental variables identified factors that may structure BMI assemblages. The BMI assemblages of three experimentally acidified and seven reference lakes at the ELA were correlated strongly with lake pH. The BMI assemblage structure of central Ontario lakes was predicted by lake area and sensitivity to acidification (NMDS dimension 1) and by lake elevation (NMDS dimension 2). The BMI assemblages of small or Ca-poor and acidic lakes include fewer oligochaetes, mayflies, and Cryptochironomus and Stictochironomus (chironomids) and more Odonata, Trichoptera, Chironomus, Conchapelopia, Microtendipes, and Procladius (chironomids), and Crangonyx (Amphipoda) than other central Ontario lakes.

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.

Physical Volcanology of An Archean Vent Complex, Minnitaki Lake area, northwestern Ontario

1977 ◽  
Author(s):  
P M Clifford ◽  
R O Page
Keyword(s):  
Lake Area ◽  
Physical Volcanology ◽  
Northwestern Ontario

Regional setting of vein-style gold mineralization around the Goldlund mine, Sandybeach Lake area, northwestern Ontario

1990 ◽  
Vol 27 (12) ◽  
pp. 1590-1608 ◽  
Author(s):  
Lesley Chorlton
Keyword(s):  
Gold Mineralization ◽  
Shear Zones ◽  
Main Body ◽  
Lake Area ◽  
Lateral Shear ◽  
Quartz Veins ◽  
Northwestern Ontario ◽  
Stage 4 ◽  
Shear Sense ◽  
Stage 1

The Sandybeach Lake area was deformed in four stages. Stage 1 produced gently south-southeast-dipping foliations at low angles to bedding. Stage 2 involved draping of these planes and formation of contact-strain aureoles related to the emplacement of granitoid stocks. Stage 3 produced doubly plunging folds, steep foliations, and shear zones, which resulted from regional transpression, with a sinistral lateral shear sense along this arm of the Wabigoon greenstone belt. Stage 4 produced minor folds and shear displacements in some places and final tightening of stage 3 folds in others, compatible with final regional convergence.Regional quartz veins, including those carrying gold, appear to have filled tensional fractures related to bulk belt-perpendicular shortening and belt-parallel extension, sinistral shear, and tightening of folds in sheetlike competent bodies. Veins and mineralization thus coincided with late stage 3 deformation, possibly overlapping stage 4.Auriferous vein occurrences at the Goldlund mine display geometries similar to those of veins in the surrounding region. The main body of auriferous vein mineralization is hosted by a thick, composite metatonalite–metadiorite sheet. The vein system of this zone likely originated during the steepening and axial-plane transposition of the southeast-dipping limb near the southwest-plunging end of a stage 3 fold.

U–Pb zircon and sphene geochronology of a composite Archean granitoid batholith, Favourable Lake area, northwestern Ontario

1985 ◽  
Vol 22 (10) ◽  
pp. 1436-1451 ◽  
Author(s):  
F. Corfu ◽  
T. E. Krogh ◽  
L. D. Ayres
Keyword(s):  
Late Stage ◽  
Temporal Correlation ◽  
Primary Crystallization ◽  
Low Grade ◽  
Lake Area ◽  
Near Surface ◽  
Chemical Alteration ◽  
Northwestern Ontario ◽  
Two Samples ◽  
Multiple Stages

U–Pb zircon and sphene data for several phases of composite batholiths in the Favourable Lake area of the Superior Province indicate two major periods of plutonism separated by a hiatus of over 200 Ma.A trondhjemite, which now forms a metamorphosed remnant within a batholith, was emplaced 2950 ± 5 Ma ago during an early plutonic event. The second and dominant plutonic period occurred between [Formula: see text] and 2711.0 ± 2.0 Ma ago; these are the ages of the earliest and the latest widespread phase of the batholiths, respectively. Ages of 2716.3 ± 1.4 and 2716 ± 4 Ma for zircons of two minor dioritic phases also fall within this interval. Metamorphic zircons about 2730 and 2715 Ma old from another unit of the batholith indicate a temporal correlation between metamorphism and main plutonic pulses.Sphenes from two samples near the margins of the batholiths yield the same age of 2711 ± 2 Ma as coexisting zircons and date the primary crystallization of the rocks. In contrast, sphenes from six samples from the interior of a batholith yield ages of 2680 ± 10 Ma, which are significantly younger than primary ages of 2950–2716 Ma of coexisting zircons. These sphene ages probably record cooling below about 500 °C during a long and complex cooling process.Several of the studied zircon populations exhibit complex discordance patterns reflecting multiple stages of Pb loss. Zircons in rocks predating the 2700–2730 Ma old metamorphic–plutonic event experienced Pb loss during this event, probably by annealing. A second low-grade event apparently caused chemical alteration of high-U zircon domains and Pb loss about 1750 Ma ago. A late stage of Pb loss affected near-surface zircon domains about 600–0 Ma ago.

Leeches (Annelida: Hirudinea) in the Experimental Lakes Area, Northwestern Ontario, Canada: Patterns of Species Composition in Relation to Environment

1994 ◽  
Vol 51 (7) ◽  
pp. 1600-1607 ◽  
Author(s):  
Brian A. Grantham ◽  
Brenda J. Hann
Keyword(s):  
Species Richness ◽  
Species Composition ◽  
Correspondence Analysis ◽  
Canonical Correspondence Analysis ◽  
Primary Productivity ◽  
Lake Area ◽  
Eutrophic Lakes ◽  
Experimental Lakes Area ◽  
Large Lakes ◽  
Northwestern Ontario

Canonical correspondence analysis (CCA) was used to examine the distribution of leeches (Annelida: Hirudinea) in 18 lakes at the Experimental Lakes Area (ELA). Leech community composition was best described by an ordination incorporating alkalinity, primary productivity, and lake area. In general, highest species richness occurred in small, eutrophic lakes whereas lowest richness was recorded in medium to large lakes with low productivity. Contrary to results for some other taxa, lake pH was not a dominant variable, describing only a small amount of variance in the species–environment relationship.

Biology of Apoidea Taken in Trap Nests in Northwestern Ontario (Hymenoptera)

1965 ◽  
Vol 97 (8) ◽  
pp. 863-877 ◽  
Author(s):  
R. E. Fye
Keyword(s):  
Plant Material ◽  
Green Plant ◽  
Lake Area ◽  
Plant Materials ◽  
Northwestern Ontario ◽  
Trap Nests

AbstractOsmia atriventris Cr. and Megachile relativa Cr. are the most abundant bees accepting trap nests in the Black Sturgeon Lake area of Ontario. Hylaeus ellipticus (Kby.), H. verticalis verticalis (Cr.), Hoplitis albifrons albifrons (Kby.), and H. cylindrica (Cr.) are common while Hylaeus basalis (Sm.), Osmia proxima Cr., M. inermis Prov., and M. gemula Cr. are comparatively rare. All except Osmia atriventris are univoltine and overwinter as prepupae. O. atriventris is both univoltine and biennial. The major flight and nesting period for all bees is during July although M. relativa is active throughout August. Hylaeus spp. construct nests of silken membranous, secreted materials; Hoplitis spp. utilize macerated plant materials and pebbles to divide their nests; Osmia spp. partition their nests with macerated green plant material; and Megachile spp. line and plug their nests in typical leafcutter fashion. All bees provision their nests with pollen moistened with varying amounts of nectar. The sexes are probably almost equally divided in all species. Major parasites are Gasteruption assectator assectator (L.) for Hylaeus spp.; Chelynia subemarginata (Cr.) for Hoplitis spp.; Sapyga sp., for Osmia atriventris; and Coelioxys modesta Sm., and C. lucrosa for Megachile relativa. Melittobia chalybii Ashm. destroyed a few cells occasionally.

ARCHAEAN SEDIMENTARY ROCKS OF NORTH SPIRIT LAKE AREA, NORTHWESTERN ONTARIO

1965 ◽  
Vol 2 (6) ◽  
pp. 622-647 ◽  
Author(s):  
J. A. Donaldson ◽  
G. D. Jackson
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Sole Source ◽  
Lake Area ◽  
Red Lake ◽  
Sedimentary Sequences ◽  
The North ◽  
Northwestern Ontario ◽  
History Of ◽  
Granitoid Rocks

Archaean sedimentary rocks of the North Spirit Lake area show little evidence of having been derived predominantly from associated Archaean volcanic rocks. Instead, compositions of the sediments reflect significant sedimentary and (or) granitoid provenance. A remarkably high content of clastic quartz in thick units of sandstone and conglomerate suggests either reworking of older quartzose sediments, or reduction of the labile constituents in quartz-rich granitoid rocks through prolonged weathering and rigorous transport. Observations for other sedimentary sequences in the region between Red Lake and Lansdowne House suggest that the North Spirit sediments are not unique in the Superior Province. Quartzose sandstones commonly are regarded as atypical of the Archaean, but such rocks arc abundant in northwestern Ontario. Frameworks of many Archaean greywackes actually are richer in quartz than typical greywackes from numerous Proterozoic and Phanerozoic sequences.The concept of rapidly rising volcanic arcs as the sole source of Archaean sedimentary detritus is rejected for the North Spirit area. The volcanies, rather than representing relicts of protocontinents, probably record events removed from initial volcanism in the history of the earth by one or more orogenic cycles. Major unconformities may therefore exist not only between sedimentary and volcanic units, but also between these units and older granitoid rocks.

Emplacement and differentiation of an Archean subvolcanic metapyroxenite–metagabbro sill in the Favourable Lake area, northwestern Ontario

1982 ◽  
Vol 19 (4) ◽  
pp. 837-858 ◽  
Author(s):  
M. Raudsepp ◽  
L. D. Ayres
Keyword(s):  
Titanium Oxide ◽  
Country Rock ◽  
Tholeiitic Basalt ◽  
Lake Area ◽  
Initial Composition ◽  
Northwestern Ontario ◽  
Volcanic Processes ◽  
Facies Metamorphism ◽  
Metasedimentary Sequence

A sequence of five fractionated, subvolcanic, pyroxenite–gabbro sills of tholeiitic basalt initial composition was intruded into the Archean Favourable Lake metavolcanic–metasedimentary sequence. Individual sills are up to 2.7 km long, range in thickness from 17 to 240 m, and are confined to a relatively thin lacustrine metachert and fine clastic unit. The sills were emplaced sequentially upward into water-rich, unlithified country rocks, with succeeding sills being emplaced prior to final consolidation of underlying sills. Sills are either in contact or separated by thin country-rock septa, but later sills did not intrude earlier sills.Greenschist facies metamorphism and pre-metamorphism alteration have destroyed primary mineralogy and have modified chemical variations, but primary textures are well preserved by pseudomorphs. Each sill comprises a lower ultramafic zone of clinopyroxene–olivine and clinopyroxene–orthopyroxene cumulates and an upper mafic zone of clinopyroxene–plagioclase – iron–titanium oxide and plagioclase – iron–titanium oxide cumulates. The upper part of the mafic zone is largely cumulus plagioclase that either accumulated in situ or floated upwards. The lower part of the ultramafic zone is relatively constant in composition and crystallization appears to have been largely in a closed system with only local magma flowage. In the mafic zone, crystallization was apparently in a more open system with surges of magma related to volcanic processes being derived either from elsewhere in the sills or externally. The most fractionated component is granophyric gabbro that is locally concentrated into large intrusive lenses.

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