Shallow crustal sounding in the Superior Province by audio frequency magnetotellurics

1978 ◽  
Vol 15 (11) ◽  
pp. 1701-1711 ◽  
Author(s):  
A. Koziar ◽  
D. W. Strangway
Keyword(s):  
Pore Space ◽  
High Resistivity ◽  
Conducting Layer ◽  
Superior Province ◽  
Audio Frequency ◽  
Magnetotelluric Soundings ◽  
Northwestern Ontario ◽  
Greenstone Belts ◽  
Very High ◽  
Made In

Audio frequency magnetotelluric soundings in the frequency range of 10 Hz to 10 kHz have been carried out over a section of the Superior Province of the Precambrian Shield in northwestern Ontario. Measurements were made in the English River sub-province, which is mainly a gneissic belt. Resistivity values over gneissic rocks and granitic intrusives were found to be generally very high. Resistivity values over greenstone belts were lower. In addition, there was a distinct conductive layering to the crust that was independent of the surface rock type.At the surface there is a thin conducting layer due to water in the surface soils and fractured rocks. Below a few tens of metres, the resistivity rises to values typically between several thousand and 100 000 ohm∙m. This is undoubtedly due to the presence of massive, unfractured rock with little water content. Beyond a depth of 7 km the resistivity drops sharply to values of 100–1000 ohm∙m. One explanation of this drop is the presence of small amounts of trapped pore-space fluids.

Age structure and orogenic significance of the Berens River composite batholiths, western Superior Province

1998 ◽  
Vol 35 (10) ◽  
pp. 1089-1109 ◽  
Author(s):  
Fernando Corfu ◽  
Denver Stone
Keyword(s):  
Age Structure ◽  
Greenstone Belt ◽  
Biotite Granite ◽  
Superior Province ◽  
Northwestern Ontario ◽  
Peraluminous Granites ◽  
Granitic Intrusions ◽  
Age Patterns ◽  
Greenstone Belts ◽  
Intrusive Activity

The Berens River area of northwestern Ontario is underlain mainly by Archean felsic plutonic rocks, which enclose minor supracrustal and gneissic enclaves and merge with the greenstone-belt-rich Uchi Subprovince to the south. U-Pb geochronology using zircon and monazite shows that the batholiths evolved mainly between 2750 and 2690 Ma by sequential and essentially continuous intrusive activity into an older substratum composed of 3000-2800 Ma volcanic and tonalitic crust. There is a broad, but not strict, compositional transition from early biotite tonalite and hornblende tonalite, progressing with time towards a greater abundance of hornblende granodiorite to granite, and finally to late biotite granite, rare peraluminous granites, and sanukitoid (dioritic, monzodioritic to granitic) plutons. The tonalite suites were predominantly synvolcanic. The late granitic intrusions postdated volcanism, but were largely synchronous with the main compressional events that caused widespread sedimentation, deformation, and metamorphism in other parts of the region. The age patterns and compositional features of the batholiths and the spatial and temporal links between their evolution and those of the supracrustal sequences in the greenstone belts of the region are consistent with mechanisms of magma generation and emplacement at converging plate margins.

U–Pb geochronology of the central Uchi Subprovince, Superior Province

1993 ◽  
Vol 30 (6) ◽  
pp. 1179-1196 ◽  
Author(s):  
F. Corfu ◽  
G. M. Stott
Keyword(s):  
Large Scale ◽  
Regional Scale ◽  
Early Period ◽  
Superior Province ◽  
Northwestern Ontario ◽  
Granitoid Rocks ◽  
Age Patterns ◽  
Tectonic Development ◽  
Greenstone Belts ◽  
Multiple Episodes

U–Pb zircon and titanite ages for rocks of the central Uchi Subprovince in northwestern Ontario indicate a late Archean magmatic and tectonic development spanning over 200 Ma. An early period at 2900–2800 Ma formed volcano-plutonic complexes, presumably linked to 3.1–2.8 Ga terrains of the northwestern Superior Province. A later period of southward growth by magmatic and tectonic accretion occurred at 2750–2710 Ma and was concluded by large scale compression and plutonism at 2700 Ma.The oldest 2890–2860 and 2840–2820 Ma components occur in the Pickle Lake and Meen–Dempster greenstone belts and as gneisses in the Seach–Achapi and the Lake St. Joseph batholiths in northern and central sectors of the region. Together with distinct 2750–2740 Ma volcano-plutonic complexes they form a collage assembled by multiple episodes of tectonic juxtaposition and magmatic accretion. Plutons of 2730–2710 Ma age are intrusive into these older, northern domains, whereas their volcanic counterparts compose the Lake St. Joseph and Miminiska – Fort Hope greenstone belts to the south. Late-tectonic to posttectonic granitoid rocks intruded a region extending from the northern Berens River Subprovince to the southern English River Subprovince at 2700 Ma. These plutons were cut by regional scale faults formed by residual north-northwest directed shortening. The timing of this movement seems to be recorded by titanite ages of 2690–2670 Ma. Reactivation of the same faults may account for Proterozoic Pb loss observed in some of the zircon populations. The age patterns are consistent with crustal growth along a continental margin in a north-dipping subduction environment.

scholarly journals The Primary Origin of Excellent Dielectric Properties of (Co, Nb) Co-Doped TiO2 Ceramics: Electron-Pinned Defect Dipoles vs. Internal Barrier Layer Capacitor Effect

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3230
Author(s):  
Theeranuch Nachaithong ◽  
Narong Chanlek ◽  
Pairot Moontragoon ◽  
Prasit Thongbai
Keyword(s):  
Dielectric Properties ◽  
Loss Tangent ◽  
Barrier Layer ◽  
Dielectric Response ◽  
High Resistivity ◽  
Low Loss ◽  
Rutile Tio2 ◽  
Complex Defect ◽  
Very High ◽  
Co Doped

(Co, Nb) co-doped rutile TiO2 (CoNTO) nanoparticles with low dopant concentrations were prepared using a wet chemistry method. A pure rutile TiO2 phase with a dense microstructure and homogeneous dispersion of the dopants was obtained. By co-doping rutile TiO2 with 0.5 at.% (Co, Nb), a very high dielectric permittivity of ε′ » 36,105 and a low loss tangent of tanδ » 0.04 were achieved. The sample–electrode contact and resistive outer-surface layer (surface barrier layer capacitor) have a significant impact on the dielectric response in the CoNTO ceramics. The density functional theory calculation shows that the 2Co atoms are located near the oxygen vacancy, creating a triangle-shaped 2CoVoTi complex defect. On the other hand, the substitution of TiO2 with Nb atoms can form a diamond-shaped 2Nb2Ti complex defect. These two types of complex defects are far away from each other. Therefore, the electron-pinned defect dipoles cannot be considered the primary origins of the dielectric response in the CoNTO ceramics. Impedance spectroscopy shows that the CoNTO ceramics are electrically heterogeneous, comprised of insulating and semiconducting regions. Thus, the dielectric properties of the CoNTO ceramics are attributed to the interfacial polarization at the internal insulating layers with very high resistivity, giving rise to a low loss tangent.

Granitoid complexes and the Archean tectonic record in the southern part of northwestern Ontario

1979 ◽  
Vol 16 (10) ◽  
pp. 1965-1977 ◽  
Author(s):  
W. M. Schwerdtner ◽  
D. Stone ◽  
K. Osadetz ◽  
J. Morgan ◽  
G. M. Stott
Keyword(s):  
Large Scale ◽  
Vertical Motion ◽  
Strike Slip ◽  
Horizontal Motion ◽  
Tectonic Deformation ◽  
Northwestern Ontario ◽  
Greenstone Belts ◽  
Second Period ◽  
Transcurrent Faults ◽  
Regional Compression

Two principal, possibly overlapping, periods of tectonic deformation can be distinguished in the Archean of northwestern Ontario, a period of dominantly vertical-motion tectonics and a period of dominantly horizontal-motion tectonics. Gigantic diapirs of foliated to gneissic tonalite–granodiorite developed during the first period and appear to be responsible for the gross structure of, and the major folds within, the metavolcanic–metasedimentary masses ("greenstone belts"). These diapirs are most likely due to mechanical remobilization of early tabular batholiths which originally intruded the oldest supracrustal rocks presently exposed. Later massive to foliated, dioritic to granitic plutons that vary from concordant, crescentic plutons to partly discordant plutons of various shapes and sizes were emplaced into the diapirs.The second period of tectonic deformation is characterized by large-scale dextral shearing and the development of major transcurrent faults under northwesterly regional compression. The strike-slip motions of this period outlasted the late plutonism, and led to the development of mylonitic zones which cut all Archean granitoid plutons.

Rubidium–strontium ages from the Oxford Lake – Knee Lake greenstone belt, northern Manitoba

1980 ◽  
Vol 17 (5) ◽  
pp. 560-568 ◽  
Author(s):  
G. S. Clark ◽  
S.-P. Cheung
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Superior Province ◽  
Granitic Intrusion ◽  
Greenstone Belts ◽  
Archean Greenstone Belts

Rb–Sr whole-rock ages have been determined for rocks from the Oxford Lake – Knee Lake – Gods Lake greenstone belt, in the Superior Province of northeastern Manitoba.The age of the Magill Lake Pluton is 2455 ± 35 Ma (λ87Rb = 1.42 × 10−11 yr−1), with an initial 87Sr/86Sr ratio of 0.7078 ± 0.0043. This granitic stock intrudes the Oxford Lake Group, so it is post-tectonic and probably related to the second, weaker stage of metamorphism.The age of the Bayly Lake Pluton is 2424 ± 74 Ma, with an initial 87Sr/86Sr ratio of 0.7029 ± 0.0001. This granodioritic batholith complex does not intrude the Oxford Lake Group. It is syn-tectonic and metamorphosed.The age of volcanic rocks of the Hayes River Group, from Goose Lake (30 km south of Gods Lake Narrows), is 2680 ± 125 Ma, with an initial 87Sr/86Sr ratio of 0.7014 ± 0.0009.The age for the Magill Lake and Bayly Lake Plutons can be interpreted as the minimum ages of granitic intrusion in the area.The age for the Hayes River Group volcanic rocks is consistent with Rb–Sr ages of volcanic rocks from other Archean greenstone belts within the northwestern Superior Province.

Magmatic and tectonic emplacement of the Pukaskwa batholith, Superior Province, Ontario, CanadaThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.

2011 ◽  
Vol 48 (2) ◽  
pp. 187-204 ◽  
Author(s):  
Gary P. Beakhouse ◽  
Shoufa Lin ◽  
Sandra L. Kamo
Keyword(s):  
Partial Melting ◽  
Abrupt Change ◽  
Superior Province ◽  
Density Inversion ◽  
Tectonic Processes ◽  
Slab Breakoff ◽  
Greenstone Belts ◽  
Lower Crustal ◽  
Basaltic Crust ◽  
Structural Dome

The Neoarchean Pukaskwa batholith consists of pre-, syn-, and post-tectonic phases emplaced over an interval of 50 million years. Pre-tectonic phases are broadly synvolcanic and have a high-Al tonalite–trondhjemite–granodiorite (TTG) affinity interpreted to reflect derivation by partial melting of basaltic crust at lower crustal or upper mantle depths. Minor syn-tectonic phases slightly post-date volcanism and have geochemical characteristics suggesting some involvement or interaction with an ultramafic (mantle) source component. Magmatic emplacement of pre- and syn-tectonic phases occurred in the midcrust at paleopressures of 550–600 MPa and these components of the batholith are thought to be representative of the midcrust underlying greenstone belts during their development. Subsequent to emplacement of the syntectonic phases, and likely at approximately 2680 Ma, the Pukaskwa batholith was uplifted as a structural dome relative to flanking greenstone belts synchronously with ongoing regional sinistral transpressive deformation. The driving force for vertical tectonism is interpreted to be density inversion (Rayleigh–Taylor-type instabilities) involving denser greenstone belts and underlying felsic plutonic crust. The trigger for initiation of this process is interpreted to be an abrupt change in the rheology of the midcrust attributed to introduction of heat from the mantle attendant with slab breakoff or lithospheric delamination following the cessation of subduction. This process also led to partial melting of the intermediate to felsic midcrust generating post-tectonic granitic phases at approximately 2667 Ma. We propose that late density inversion-driven vertical tectonics is an inevitable consequence of horizontal (plate) tectonic processes associated with greenstone belt development within the Superior Province.

FUNGI IN AIR MASSES OVER MONTREAL DURING 1950 AND 1951

1956 ◽  
Vol 34 (1) ◽  
pp. 1-15 ◽  
Author(s):  
S. M. Pady ◽  
L. Kapica
Keyword(s):  
Seasonal Variation ◽  
Pollen Grains ◽  
Average Concentration ◽  
Yeast Cells ◽  
The Sun ◽  
Air Masses ◽  
Air Sampler ◽  
Agricultural Areas ◽  
Very High ◽  
Made In

Numbers and kinds of fungi were determined from nutrient plate and silicone slide studies from the roof of the Sun Life Building, Montreal, between September 1950 and December 1951. Exposures of plates were made in the General Electric Bacterial Air Sampler, and plates and silicone slides in the Bourdillon Slit Sampler. A total of 978 exposures was made on 113 sampling days during 16 months; 507 plates in the G. E. Sampler, 344 plates and 127 slides in the Slit Sampler. Of 40,359 colonies examined, Cladosporium, Penicillium, yeasts, Aspergillus, Alternaria, and Actinomycetes were commonest, constituting 47.7, 15.8, 10.4, 4.6, 4.2, and 2.2% of the total. The next commonest fungi were Pullularia, Oöspora, Fusarium, Stemphylium, Verticillium, Rhizopus, Spicaria, Scopulariopsis, Phoma, Mucor, Botrytis, Cephalosporium, Trichoderma, Helmin-thosporium, Neurospora, Papularia, Cephalothecium, Pyrenochaeta, Zythia, and Nigrospora. In addition 12 genera were infrequently found. Unidentified colonies numbered 174 and nonsporulating 3371 (8.3%). On a cubic foot basis numbers in the plates varied from 17.7 per cu. ft. in August to 0.4 per cu. ft in February.Fungus spores showed a seasonal variation with summer highs averaging 244 per cu. ft. in July to a low of 0.8 per cu. ft. in December. The most abundant spores were Cladosporium, yeasts, smuts, Fusarium, Alternaria, Venturia-like, Stemphylium, rusts, Septoria, and Helminthosporium. Hyphal fragments and pollen grains were present also. On eight occasions during the summer, readings of over 200 spores per cu. ft. were recorded, the maximum being 445 per cu. ft. on September 6, 1951. Cladosporium in August reached a peak of 74.1 per cu. ft. and yeast cells in July had an average concentration of 100 per cu. ft.An analysis of the air masses indicated that pure polar air carried low numbers of fungi, whereas tropical air had very high numbers. Most of the air masses were modified polar air and their fungus content varied considerably. The fungi in the air over Montreal are believed to have had their origin in agricultural areas.

Flow Field on Helodeck of a Frigate: A Review

2019 ◽  
Vol 161 (A4) ◽  
Keyword(s):  
Flow Field ◽  
Numerical Solutions ◽  
Offshore Structures ◽  
High Speeds ◽  
High Turbulence ◽  
The Subject ◽  
Offshore Industry ◽  
The Military ◽  
Very High ◽  
Made In

The various functions desired from a frontline warship such as a frigate, corvette or a destroyer, coupled with the requirement of very high speeds and economic viability restricting the size, necessitates a very dense arrangement of weapons and sensors on the top deck and superstructure. Accordingly, Navies across the world have faced several problems with respect to functions for which a good aerodynamic design for these structures is essential. Major issues include smoke nuisance created due to impinging of the ship's exhaust gases on to the top deck leading to possible suction by engine intakes and high turbulence in the ship's air-wake leading to ship aircraft interface concerns. The flow field on the helodeck is extremely complex due to its geometry and interaction with the wake of the ship’s superstructure. A knowledge of this complexity is essential for ensuring safe helo operations on the helodeck. The problem of ship helicopter interaction has hogged the lime light in recent times, due to rising demand for design of warships for increased stealth, especially in the past two decades. Consequently, several researchers in countries with advanced Navies have invested considerable resources towards evolving both experimental and numerical solutions for the problem. However, given the military nature of the operations, open literature on the subject containing details of such research, which can be used as reference material for present work, are limited. Considering the complexities involved in the problem, an attempt has been made in this paper to holistically review the widely scattered and limited literature in this field. A good amount of literature on marine helo applications emerge from the offshore industry. Keeping in mind that the fields of warship design and offshore structures are dissimilar and have their peculiar problems, informed conclusions have been made in drawing lessons from available literature.

scholarly journals Moving Forward With Accelerometer-Assessed Physical Activity: Two Strategies to Ensure Meaningful, Interpretable, and Comparable Measures

2018 ◽  
Vol 30 (4) ◽  
pp. 450-456 ◽  
Author(s):  
Alex V. Rowlands
Keyword(s):  
Physical Activity ◽  
Black Box ◽  
Data Sets ◽  
Accelerometer Data ◽  
Future Health ◽  
The Past ◽  
Acceleration Data ◽  
Night And Day ◽  
Very High ◽  
Made In

Significant advances have been made in the measurement of physical activity in youth over the past decade. Monitors and protocols promote very high compliance, both night and day, and raw measures are available rather than “black box” counts. Consequently, many surveys and studies worldwide now assess children’s physical behaviors (physical activity, sedentary behavior, and sleep) objectively 24 hours a day, 7 days a week using accelerometers. The availability of raw acceleration data in many of these studies is both an opportunity and a challenge. The richness of the data lends itself to the continued development of innovative metrics, whereas the removal of proprietary outcomes offers considerable potential for comparability between data sets and harmonizing data. Using comparable physical activity outcomes could lead to improved precision and generalizability of recommendations for children’s present and future health. The author will discuss 2 strategies that he believes may help ensure comparability between studies and maximize the potential for data harmonization, thereby helping to capitalize on the growing body of accelerometer data describing children’s physical behaviors.

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