Estimates of distortional strain in mylonites from the Grenville Front Tectonic Zone, Tomiko area, Ontario

1977 ◽  
Vol 14 (8) ◽  
pp. 1708-1720 ◽  
Author(s):  
S. G. Themistocleous ◽  
W. M. Schwerdtner
Keyword(s):  
Real Root ◽  
Total Strain ◽  
Tectonic Zone ◽  
Grenville Province ◽  
Boundary Fault ◽  
Cubic Equation ◽  
Front Boundary ◽  
Strain Components ◽  
Superior Portion ◽  
Minimal Measure

The Grenville Front Tectonic Zone extends as much as 30 km into the Grenville Province of Ontario, but reaches only a few kilometres into the Superior and Southern Provinces. For a distance of >75 km, this tectonic zone passes through a large granitic body, the Ingall Lake Batholith. Here the Superior portion of the zone is characterized by numerous north to northeast trending faults which cut the Grenville Front Boundary Fault. One of these younger structures, the Kettle Lake Fault, is exposed on Highway 11 about 1 km north of the Grenville Front Boundary Fault. Its mylonites are generally derived from feldspar-porphyritic trondhjemite, and contain numerous folded dykes of pink aplite.The folds plot into J. G. Ramsay's class 1C field, and represent flattened buckles. Using Ramsay's methods, C/B (flattening) and C (buckling) were estimated for the preserved parts of seven minor folds. The remaining components of overall strain were calculated on the basis of k-values obtained for the mylonitic trondhjemite adjacent to the buckles. Susceptibility anisotropy determinations provided an objective but minimal measure of k. The dilatational part of the deformation was ignored by putting ABC = 1. Thus for B (buckling) we found that B3 − B2C(1 −(1/k)) − 1/k = 0. This cubic equation has one real root B and two conjugate imaginary roots. Similarly for the flattening phase, A/B = 1 − k(1 − (B/C). Total strain components were obtained by superimposing the flattening strain on the buckling strain. Maximum values of C range from 0.081 to 0.395 depending on the severity of mylonitization.

A seismic-based cross-section of the Grenville Orogen in southern Ontario and western Quebec

2000 ◽  
Vol 37 (2-3) ◽  
pp. 183-192 ◽  
Author(s):  
D J White ◽  
D A Forsyth ◽  
I Asudeh ◽  
S D Carr ◽  
H Wu ◽  
...  
Keyword(s):  
Cross Section ◽  
Seismic Refraction ◽  
Shear Zones ◽  
Tectonic Zone ◽  
Grenville Province ◽  
Crustal Layer ◽  
Seismic Reflection Data ◽  
Velocity Models ◽  
Laurentian Margin ◽  
Structural Boundary

A schematic crustal cross-section is presented for the southwestern Grenville Province based on reprocessed Lithoprobe near-vertical incidence seismic reflection data and compiled seismic refraction - wide-angle velocity models interpreted with geological constraints. The schematic crustal architecture of the southwest Grenville Province from southeast to northwest comprises allochthonous crustal elements (Frontenac-Adirondack Belt and Composite Arc Belt) that were assembled prior to ca. 1160 Ma, and then deformed and transported northwest over reworked rocks of pre-Grenvillian Laurentia and the Laurentian margin primarily between 1120 and 980 Ma. Reworked pre-Grenvillian Laurentia and Laurentian margin rocks are interpreted to extend at least 350 km southeast of the Grenville Front beneath all of the Composite Arc Belt. Three major structural boundary zones (the Grenville Front and adjacent Grenville Front Tectonic Zone, the Central Metasedimentary Belt boundary thrust zone, and the Elzevir-Frontenac boundary zone) have been identified across the region of the cross-section based on their prominent geophysical signatures comprising broad zones of southeast-dipping reflections and shallowing of mid-crustal velocity contours by 12-15 km. The structural boundary zones accommodated southeast over northwest crustal stacking at successively earlier times during orogeny (ca. 1010-980 Ma, 1080-1060 Ma, and 1170-1160 Ma, respectively). These shear zones root within an interpreted gently southeast-dipping regional décollement at a depth of 25-30 km corresponding to the top of a high-velocity lower crustal layer.

Interplay between folding and ductile shearing in the Proterozoic crust of the Muskoka – Parry Sound region, central Ontario

1987 ◽  
Vol 24 (8) ◽  
pp. 1507-1525 ◽  
Author(s):  
W. M. Schwerdtner
Keyword(s):  
Large Scale ◽  
Lake Huron ◽  
Ductile Deformation ◽  
Boundary Fault ◽  
Crustal Thinning ◽  
Front Boundary ◽  
Ductile Shearing ◽  
Structural Signature ◽  
Reverse Shearing ◽  
East West

Grenville gneiss of the central Georgian Bay region was subjected to ductile deformation that produced narrow mylonite zones as well as three sets of superimposed folds differing greatly in structural signature, size, and orientation. Some mylonite zones are concordant to gneissosity and are repeatedly folded, others cut gneissosity and postdate the folding. Gneissosity was generated as a regionally subhorizontal feature, either by crustal thinning or, like the early mylonite zones, by low-angle reverse shearing. An attempt is made to account for the initially subhorizontal gneissosity, the mylonite zones, and the folds in a regime of large-scale reverse shearing that strikes parallel to the Grenville Front.Upright northwest–southwest to north–south buckle folds dominate the map pattern and are subperpendicular to the reverse Grenville Front boundary fault. These set-2 folds cannot be attributed to reverse simple shearing but require a large component of east–west compression. Such stress could have been generated in a northwest–southeast zone of sinistral ductile shear caused by temporary locking of the southern segment of the Grenville Front boundary fault (now under Lake Huron).All structural facts can be explained without large differential translations of crustal slices. For example, most discordances in the regional gneissosity pattern could have been created by décollement and repeated buckling. Detailed geobarometry and petrologic studies may be required to settle the question of large-scale thrusting within the Grenville gneiss terrane.

Progressive metamorphism of pelitic and quartzofeldspathic rocks in the Grenville Province of western Labrador — tectonic implications of bathozone 6 assemblages

1983 ◽  
Vol 20 (12) ◽  
pp. 1791-1804 ◽  
Author(s):  
T. Rivers
Keyword(s):  
Experimental Data ◽  
Pressure Gradient ◽  
Granulite Facies ◽  
Lithostatic Pressure ◽  
Lower Grade ◽  
High Grade ◽  
Tectonic Zone ◽  
Grenville Province ◽  
Mineral Assemblages ◽  
Grenvillian Orogeny

Aphebian metapelites and quartzofeldspathic rocks from the Grenville Province south of the Labrador Trough display progressive changes in mineral assemblages as a result of Grenvillian metamorphism, consistent with variation in grade from greenschist to upper amphibolite facies. The following metamorphic zones have been delineated: (i) chlorite–muscovite; (ii) chlorite–muscovite–biotite; (iii) chlorite–muscovite–biotite–garnet; (iv) muscovite–staurolite–kyanite; (v) muscovite–garnet–biotite–kyanite; (vi) muscovite–garnet–biotite–kyanite–granitic veins; (vii) K–feldspar–kyanite – granitic veins; (viii) K-feldspar–sillimanite–granitic veins. Reactions linking the lower grade metamorphic zones are interpreted to be dehydration phenomena, whilst anatectic reactions occur at higher grades. At lower metamorphic grades aH2O was high [Formula: see text] but it declined progressively as water entered the melt phase during higher grade anatectic reactions. With the onset of vapour-absent anatexis, the restite assemblage became essentially "dry" [Formula: see text], and biotite breakdown occurred in granulite-facies rocks east of the study area. Consideration of available experimental data suggests that metamorphic temperatures ranged from approximately 450 to 750 °C across the study area. Lithostatic pressure during metamorphism reached about 8 kbar (800 MPa) in the high-grade zones, with estimates at lower grades being poorly constrained; however, a steep pressure gradient across the map area is postulated.This is the first reported occurrence of bathozone 6 assemblages from a progressive metamorphic sequence, and it indicates the presence of an unusually great thickness of supracrustal rocks during the Grenvillian Orogeny. This was achieved by imbricate stacking of thrust slices, perhaps doubling the thickness of the crust in the Grenville Front Tectonic Zone, creating a huge gravity anomaly of which a remnant still persists today.

La zone tectonique du front de Grenville à l'est de Louvicourt, Québec : exhumation de la croûte archéenne pendant l'orogénie grenvillienne

1995 ◽  
Vol 32 (11) ◽  
pp. 1899-1920 ◽  
Author(s):  
Alain Berclaz ◽  
Réjean Hébert ◽  
Michel Rocheleau
Keyword(s):  
Regional Metamorphism ◽  
Volcanic Rocks ◽  
Crustal Thickening ◽  
Coarse Grained ◽  
Superior Province ◽  
Reverse Fault ◽  
Tectonic Zone ◽  
Grenville Province ◽  
Vein Formation ◽  
Lower Temperature

The Grenville Front tectonic zone, East of Louvicourt in Quebec, defines a tectonometamorphic domain marked by the Grenville Front oriented North 50°, that is locally crosscut by a North 30° reverse fault, the Matchi-Manitou Fault. These tectonic accidents separate the central parts of the Superior Province to the northwest from the Grenville Province to the southeast. The Archean age, high-grade polymetamorphic sequences of the Grenville Province consist of paragneisses and migmatitic quartzofeldspathic gneisses associated to coarse-grained, anatectic pegmatitic veins, the whole containing shreds of two pyroxenes-bearing mafic gneisses. The metamorphic disequilibrium textures, the chemical analyses of the mineral phases, and the whole-rock chemistry of these sequences indicate that a strong crustal thickening, marked by the incorporation of shreds of volcanic rocks in the metasedimentary sequences, led to the granulitization of the lithologies and the quartzofeldspathic pegmatitic vein formation by fluid-absent partial melting of the surrounding migmatitic quartzofeldspathic gneisses under 750–825 MPa and 675–745 °C conditions. Subsequently, a higher pressure and slightly lower temperature episode (920–990 MPa and 625–750 °C) is at the origin of a development of secondary coronitic garnet around primary garnet. A late fluid is responsible for final retrograde reequilibrations in all the lithologies. All these successive events probably occurred during the Archean ages. During the Grenvillian orogeny (1.0 Ga), the thrusting movement with a strong sinistral component of the Grenvillian Province onto the Superior Province is characterized: (i) to the east of the Grenville Front, by the exhumation and the rotation of 9–12 km thick sequences of the Grenville Province; (ii) to the west of the Grenville Front, by the development of a 705–845 MPa and 570–605 °C medium-grade metamorphism that overprints the 400–565 MPa and 600–660 °C regional metamorphism of Kenorean age. Both metamorphic episodes define a 1–6 km width band made of biotite and garnet-bearing paragneisses.

40Ar/39Ar traverse ? Grenville Front Tectonic Zone to Britt Domain, Grenville Province, Ontario, Canada

1995 ◽  
Vol 13 (2) ◽  
pp. 209-221 ◽  
Author(s):  
P. H. REYNOLDS ◽  
N. G. CULSHAW ◽  
R. A. JAMIESON ◽  
S. L. GRANT ◽  
K. J. McKENZIE
Keyword(s):  
Tectonic Zone ◽  
Grenville Province

The velocity structure of the Britt Domain, southwestern Grenville Province, from laboratory and refraction experiments

1996 ◽  
Vol 33 (5) ◽  
pp. 729-745 ◽  
Author(s):  
C. Long ◽  
M. H. Salisbury
Keyword(s):  
Velocity Structure ◽  
Acoustic Properties ◽  
P Wave ◽  
Granitic Rocks ◽  
S Wave ◽  
Granitic Gneiss ◽  
Tectonic Zone ◽  
Grenville Province ◽  
Near Surface ◽  
Wave Velocities

The Britt Domain in the southwestern Grenville Province of the Canadian Shield is believed to be an exposure of high-grade (upper amphibolite facies) mid-crustal rocks of predominantly granitic and granodioritic composition. A 270 km refraction line was conducted by Lithoprobe across the Britt Domain and the Grenville Front Tectonic Zone to the north in order to determine the deep velocity structure under the region. This data set demonstrates a uniform velocity structure to a depth of 15 km in the central Britt Domain, with near-surface P- and S-wave velocities of 6.15 and 3.55 km/s, respectively, and linear vertical gradients at depth of 0.02 and 0.01 s−1, respectively. The data also show that the Grenville Front Tectonic Zone is strongly anisotropic at shallow depths. To determine the acoustic properties of rocks from the Britt Domain, 80 velocity samples representing different lithologies in this area were measured at confining pressure up to 600 MPa. These studies show that P-wave velocities at 600 MPa range from 6.29 km/s (granitic gneiss) through 6.51 km/s (intermediate gneiss) to 6.90 km/s (mafic rocks), and have an area-weighted mean of 6.36 ± 0.08 km/s. S-wave velocities for selected samples range from 3.54 km/s (paragneiss) through 3.62 km/s (granitic gneiss) to 4.04 km/s (amphibolite). P-wave velocity anisotropy is weak in the granitic rocks (1.1% on average), but stronger in paragneisses and amphibolites from the region (5.2–5.9%). Comparison of laboratory and refraction data suggests that the Britt Domain is granodioritic in composition to mid-crustal levels. The lower crust beneath the Grenville Front Tectonic Zone in the central Britt Domain appears to be composed of diorite at the top, but becomes increasingly mafic toward the Moho.

Pairs of Spherical Mirrors as Prime Focus Correctors for the Anglo-Australian Telescope

1972 ◽  
Vol 2 (3) ◽  
pp. 126-127 ◽  
Author(s):  
N. J. Rumsey
Keyword(s):  
Real Root ◽  
Early Stage ◽  
Spherical Aberration ◽  
Primary Mirror ◽  
The Real ◽  
Real Roots ◽  
Algebraic Analysis ◽  
Cubic Equation ◽  
Spherical Mirrors ◽  
Aberration Corrected

Last year I described pairs of spherical mirrors that remove the coma and astigmatism in the image formed by a paraboloid mirror and leave the spherical aberration corrected. The investigation can be extended to deal with other shapes of primary mirror, for example the hyperboloid primary of the Anglo-Australian Telescope. The algebraic analysis becomes more complicated than for a paraboloid; but it still has the feature that at an early stage a cubic equation has to be solved, each real root of which gives rise to a second cubic. Thus in principle the mathematics could lead to nine solutions. However, it again turns out that not all the roots are real; and even for the real roots not all the solutions are physically useful, because in some cases the final image is virtual, and in others the tertiary mirror lies behind the secondary where light can not reach it. When the primary is a paraboloid, there are three useable solutions all with the property that the field corrector (consisting of the pair of spherical mirrors) can simply be scaled up or down at the user’s pleasure according to the diameter of the field he wishes to photograph. When the primary is of any other shape this is no longer possible.

Sm–Nd isotopic evidence for crustal contamination in the ca. 1750 Ma Wanapitei Complex, western Grenville Province, Ontario

1995 ◽  
Vol 32 (4) ◽  
pp. 486-495 ◽  
Author(s):  
S. A. Prevec
Keyword(s):  
Rare Earth ◽  
Earth Element ◽  
Crustal Contamination ◽  
Crustal Material ◽  
Zircon Geochronology ◽  
Light Rare Earth ◽  
Text Data ◽  
Grenville Province ◽  
Front Boundary ◽  
Depleted Mantle

The Wanapitei Complex consists of a variably metamorphosed gabbronorite lying immediately adjacent to the Grenville Front Boundary Fault. U–Pb zircon geochronology indicates a crystallization age of [Formula: see text] for a noritic component, with both Grenville-aged (ca. 1000 Ma) metamorphism and minor older inheritance indicated. Geochemical evidence is consistent with plagioclase–pyroxene fractionation, but indicates additional open-system behaviour. [Formula: see text] data indicate contamination of a depleted mantle by light rare earth element-enriched material during the Penokean. This was followed during emplacement by extensive contamination of the then isotopically near-chondritic magma with variable amounts of evolved Archean crustal material, on the order of 40% in extreme cases, generating εNd(1.75) values between 0 and −7.5.

scholarly journals Solution of A Cubic Equation with Triangular Number as Coefficients

2019 ◽  
Vol 8 (3) ◽  
pp. 8867-8870
Keyword(s):  
Continued Fraction ◽  
Real Root ◽  
Trial And Error ◽  
The Real ◽  
Cubic Equation ◽  
Triangular Number ◽  
Polygonal Numbers ◽  
Trial And Error Method ◽  
Fraction Method ◽  
Error Method

While solving a cubic equation one root is always identified using trial and error method. Here in this paper first the interval in which the real root appears is found and the real root is identified using continued fraction method. It is illustrated by an equation having polygonal numbers as coefficients

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