A test of detailed Nd isotope mapping in the Grenville Province: delineating a duplex thrust sheet in the Kipawa–Mattawa region

2006 ◽  
Vol 43 (4) ◽  
pp. 421-432 ◽  
Author(s):  
M K Herrell ◽  
A P Dickin ◽  
W A Morris
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Data Sets ◽  
Aeromagnetic Data ◽  
Thrust Sheet ◽  
Grenville Province ◽  
Nd Isotope ◽  
Tectonic Model ◽  
Thrust Sheets ◽  
Archean Crust

Over sixty new neodymium model ages were determined on orthogneisses from the Kipawa–Mattawa region of the Grenville Province to refine previous Nd isotope mapping work in this area. The combined Nd data sets support a tectonic model involving three major thrust sheets in the Kipawa area, separated by major shear zones. The uppermost sheet is correlated with the Allochthonous Polycyclic Belt, represented in the study area by the Lac Watson nappe, along with two allochthonous klippen. These have Nd model ages < 1.8 Ga, consistent with previous work. Within the underlying Parautochthonous Belt, previous workers identified a second major shear zone, separating rocks with Archean and Proterozoic crystallization ages, respectively. These two thrust sheets also have distinct Nd isotope signatures. The lowermost sheet consists of metamorphosed but otherwise relatively pristine Archean crust with Nd model ages > 2.6 Ga, whereas the overlying sheet consists of magmatically reworked Archean parautochthon with model ages from 1.8–2.6 Ga. A residual magnetic-field map developed from aeromagnetic data was compared with the terrane boundaries determined from isotopic data. The aeromagnetic data accurately reflect the margin of relatively pristine Archean crust in the study area, but this boundary does not correspond to the Allochthon Boundary Thrust. Instead, this boundary resulted from downcutting of the basal shear zone of the allochthon. This caused décollement of the strongly reworked Archean parautochthon to generate a duplex thrust sheet that was transported northwestwards over pristine Archean crust.

Geophysical characteristics of the continental crust along the Lithoprobe Eastern Canadian Shield Onshore–Offshore Transect (ECSOOT): a review

2002 ◽  
Vol 39 (5) ◽  
pp. 569-587 ◽  
Author(s):  
Jeremy Hall ◽  
Keith E Louden ◽  
Thomas Funck ◽  
Sharon Deemer
Keyword(s):  
Normal Incidence ◽  
Shear Zones ◽  
Canadian Shield ◽  
P Wave ◽  
Seismic Profiles ◽  
Grenville Province ◽  
Core Zone ◽  
The Core ◽  
Geodynamic Processes ◽  
Archean Crust

The Eastern Canadian Shield Onshore–Offshore Transect (ECSOOT) of the Lithoprobe program included 1200 km of normal-incidence seismic profiles and seven wide-angle seismic profiles across Archean and Proterozoic rocks of Labrador, northern Quebec, and the surrounding marine areas. Archean crust is 33–44 km thick. P-wave velocity increases downwards from 6.0 to 6.9 km/s. There is moderate crustal reflectivity, but the reflection Moho is unclear. Archean crust that stabilized in the Proterozoic is similar except for greater reflectivity and a well-defined Moho. Proterozoic crust has similar or greater thickness, variable lower crustal velocities, and strong crustal reflectivity. Geodynamic processes of Paleoproterozoic growth of the Canadian Shield are similar to those observed in modern collisional orogens. The suturing of the Archean Core Zone and Superior provinces involved whole-crustal shearing (top to west) in the Core Zone, linked to thin-skinned deformation in the New Quebec Orogen. The Torngat Orogen sutures the Nain Province to the Core Zone and reveals a crustal root, in which Moho descends to 55 km. It formed by transpression and survived because of the lack of postorogenic heating. Accretion of the Makkovik Province to the Nain Province involves delamination at the Moho and distributed strain in the juvenile arcs. Delamination within the lower crust characterizes the accretion of Labradorian crust in the southeastern Grenville Province. Thinning of the crust northwards across the Grenville Front is accentuated by Mesozoic extension that reactivates Proterozoic shear zones. The intrusion of the Mesoproterozoic Nain Plutonic Suite is attributed to a mantle plume ponding at the base of the crust.

Nd isotope mapping of the Lac Dumoine thrust sheet: implications for large-scale crustal structure in the SW Grenville Province

Terra Nova ◽  
2012 ◽  
Vol 24 (5) ◽  
pp. 363-372 ◽  
Author(s):  
Alan P. Dickin ◽  
David Cooper ◽  
Anlin Guo ◽  
Cara Hutton ◽  
Chris Martin ◽  
...  
Keyword(s):  
Crustal Structure ◽  
Large Scale ◽  
Thrust Sheet ◽  
Grenville Province ◽  
Nd Isotope

A structural analysis of a metamorphic fold–thrust belt, northeast Gagnon terrane, Grenville Province

1992 ◽  
Vol 29 (9) ◽  
pp. 1915-1927 ◽  
Author(s):  
Dennis Brown ◽  
Taoby Rivers ◽  
Tom Calon
Keyword(s):  
Deep Level ◽  
Greenschist Facies ◽  
Thrust Belt ◽  
Structural Elements ◽  
Thrust Sheet ◽  
Grenville Province ◽  
Lake Formation ◽  
Transport Direction ◽  
Tectonic Transport ◽  
Thrust Sheets

Northeast Gagnon terrane is located within the Parautochthonous Belt of the Grenville Orogen, near the projected intersection of the front zones of the Grenville and New Quebec orogens. The area consists principally of supracrustal units of the Early Proterozoic Knob Lake Group, and a newly recognized unit, the Equus Lake formation. Both are intruded by the Middle Proterozoic Shabogamo gabbro. Structural elements in the rocks record evidence of a polyorogenic history that is attributed to both the ca. 1800 Ma Hudsonian and the ca. 1000 Ma Grenvillian orogenies. This paper is concerned with the latter.Grenvillian deformation resulted in the formation of a relatively deep-level fold–thrust belt. Three thrust sheets can be defined on the basis of basal thrusts, variations in morphology and orientation of structural elements, and internal thrust sheet geometry. The polydeformational style of the area, rotation of fold axes into subparallelism with the tectonic transport direction, and internal imbrication lead to a complex internal thrust sheet geometry. Thrusting has produced and inverted the metamorphic gradient, with lower greenschist facies in the basal thrust sheet and upper greenschist facies in the upper thrust sheet.Documentation of the northeastern margin of Gagnon terrane as a north- to northwest-directed metamorphic fold–thrust belt corroborates similar interpretations for Gagnon terrane from elsewhere along the Grenville Front and is in accord with the models of the Grenville Province as a collisional orogen. Furthermore, it is suggested that northeast Gagnon terrane is an exhumed, internal, ductile part of a fold–thrust belt.

Deep-crustal deformation textures along megathrusts from Newfoundland and Ontario: implications for microstructural preservation, strain rates, and strength of the lithosphere

1992 ◽  
Vol 29 (2) ◽  
pp. 328-337 ◽  
Author(s):  
Joseph Clancy White ◽  
Christopher K. Mawer
Keyword(s):  
Shear Zone ◽  
Upper Mantle ◽  
Shear Zones ◽  
Threshold Temperature ◽  
Strain Rates ◽  
Grenville Province ◽  
Preservation Condition ◽  
Deformation Textures ◽  
Highly Strained ◽  
Lower Crustal

Lithospheric-scale thrusts from the west Newfoundland ophiolite belt (White Hills Peridotite shear zone) and the south-western Grenville Province (Parry Sound shear zone) involve rocks of lower crustal and (or) upper mantle origin that exhibit intense crystal-plastic deformation of plagioclase, K-feldspar, orthopyroxene, and clinopyroxene, minerals that are commonly viewed as representative of low-ductility phases. The occurrence of this extreme deformation in shear zones that exhibit similar lower crustal syntectonic P–T conditions suggests a phenomenological link between the megathrust environment and both the generation and subsequent preservation of the observed deformation microstructures. An empirical homologous parameter is constructed in an attempt to characterize conditions for similar behaviour among different minerals and to explore the feasibility of refining a threshold recovery–preservation condition within the megathrusts studied. This parameter predicts, at the estimated syntectonic temperature of 800 °C, the similarity of microstructures in highly strained albite and orthopyroxene crystals observed in both megathrusts. This temperature is interpreted as a lower limit for the upper threshold of microstructure preservation in albite and orthopyroxene for the particular megathrust history. Comparison of tectonic constraints with strain rates calculated at the inferred threshold temperature for several minerals with tectonic constraints indicates that strain rates of at least 10−12 s−1 are both rheologically possible and geometrically plausible in shear zones of kilometre-scale widths. The associated lithosphere strength during megathrust displacement is on the order of 1–50 MPa. These data support formation of synkinematic records within shear zones that preserve evidence of lithospheric behaviour over crustal-thickness length scales.

Ductile thrusting at mid-crustal level, southwestern Grenville Province

1988 ◽  
Vol 25 (7) ◽  
pp. 1049-1059 ◽  
Author(s):  
Simon Hanmer
Keyword(s):  
Shear Zones ◽  
Wall Rock ◽  
Grenville Province ◽  
Low Viscosity ◽  
Ductile Shear Zones ◽  
Thrust Sheets ◽  
Grenvillian Orogeny ◽  
Central Gneiss Belt ◽  
Viscosity Fluid ◽  
Extensional Structures

The northwestern boundary zone of the Central Metasedimentary Belt (Grenville Province) in the Haliburton area (Ontario) is a stack of alternating tonalitic and syenitic crystalline thrust sheets, transported toward the northwest on out-of-sequence, upper amphibolite facies, ductile thrust zones during the Grenvillian Orogeny, at 1060 Ma, approximately 100 Ma after the initiation of thrusting in the underlying Central Gneiss Belt. Kinematics of the deformation are complex. Predominant northwestward thrusting was, at least partly, coeval with subordinate northeastward thrusting. Late synmetamorphic extensional shears cut both thrusts and thrust sheets. Minor late thrusting on discrete ductile shear zones postdates the extensional structures. Belts of mechanically weak pelite(?) appear to have localised the thrust sheets. Highly mobile marble behaved as a relatively low viscosity fluid during transport, able to intrude and erode more competent wall rock.

Is the Cape Smith Belt (northern Quebec) a klippe?

1985 ◽  
Vol 22 (9) ◽  
pp. 1361-1369 ◽  
Author(s):  
Paul F. Hoffman
Keyword(s):  
Shear Zone ◽  
Granulite Facies ◽  
Magnetic Anomalies ◽  
Ductile Shear Zone ◽  
Tectonic Model ◽  
The North ◽  
Thrust Sheets ◽  
Ductile Shear ◽  
Normal Sense ◽  
East West

The Cape Smith Belt is one of the most interesting and controversial of the proposed geosutures in the Canadian Shield. A new tectonic model is presented in which the mafic–ultramafic thrust sheets of the belt constitute a klippe, 20 000 km2 in area, separated from underlying basement of Superior Province and its thin autochthonous cover by a continuous décollement exposed along the north margin and the plunging eastern end of the belt. Thrusting is directed southward, and the entire stack is folded into a regional antiform (north of the belt) and synform (the belt itself). It is proposed that the décollement is rooted 30–90 km north of the belt, in a zone paralleling Sugluk Inlet, across which there is a major positive deflection in the Bouguer gravity field, an abrupt switch from broad north–south to narrow east–west magnetic anomalies, and a change in metamorphic grade from amphibolite to granulite facies from south to north. In the model, this zone is a north-dipping ductile shear zone juxtaposing crusts of two collided continents. Accordingly, granulite north of the zone represents lower crust of the overriding plate, whereas granulite between the zone and the klippe occurs in antiformal culminations in the underriding plate. One test of the model is that the south-dipping shear zone observed at the north margin of the belt should have a normal sense of slip. Another is that north-dipping banded gneiss at Sugluk Inlet should mark a ductile shear zone, also having a south-directed sense of overthrusting. A structural profile of the belt and its relation to basement can best be worked out by down-plunge projection of the eastern end of the belt.

The age of the Lac-Saint-Jean Anorthosite Complex and associated mafic rocks, Grenville Province, Canada

1992 ◽  
Vol 29 (7) ◽  
pp. 1412-1423 ◽  
Author(s):  
Michael D. Higgins ◽  
Otto van Breemen
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Strike Slip ◽  
Short History ◽  
Southwestern Part ◽  
Grenville Province ◽  
South Central ◽  
History Of ◽  
Emplacement Mechanism ◽  
Anorthosite Complex

U–Pb analyses of zircon and baddeleyite from the south-central and southeastern parts of the Lac-Saint-Jean Anorthosite Complex (LSJA) give an igneous crystallization age of 1157 ± 3 Ma. Parts of the anorthosite were deformed in the solid state and subsequently intruded by a diorite megadyke, which also gives a crystallization age of 1157 ± 3 Ma, indicating that crystallization and deformation of the anorthosite were essentially synchronous. The diorite megadyke was intruded into a north-northeast-trending shear zone and deformed by sinistral strike-slip movements. Emplacement was followed by intrusion of a subparallel leucotroctolite megadyke that again gives the same crystallization age and hence dates movement of the shear zone at 1157 ± 3 Ma. This short history of crystallization and synchronous deformation rules out slow diapiric rise as the emplacement mechanism for the anorthosite. Instead, anorthosite parental magmas probably rose up offsets in subvertical strike-slip shear zones to their present level.In the southwestern part of the LSJA an age of 1142 ± 3 Ma is interpreted to represent igneous crystallization. Contemporary thermal metamorphic effects recorded in the southeastern sector by growth of new zircon in granophyric segregations and zircon coronas on baddeleyite suggest this event was more widespread at slightly deeper levels. Evidence has not been found for a separate Grenville regional metamorphism.The emplacement into the LSJA at 1076 ± 3 Ma of two small leucogabbro intrusions was part of a widespread magmatic event similar to the main event at 1157–1142 Ma.

Quartz microstructures and c-axis preferred orientations in high-grade gneisses and mylonites around the Morin anorthosite (Grenville Province)

1997 ◽  
Vol 34 (6) ◽  
pp. 819-832 ◽  
Author(s):  
Xiao-ou Zhao ◽  
Shaocheng Ji ◽  
Jacques Martignole
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Granulite Facies ◽  
High Grade ◽  
Grenville Province ◽  
The North ◽  
Deformation Features ◽  
Type 3

Quartz in deformed rocks from two large, high-grade shear zones around the Morin anorthosite (Morin terrane, Grenville Province) displays distinctive microstructures, as well as c-axis preferred orientations. In the west-dipping Morin shear zone, east of the Morin anorthosite, four distinct quartz microstructures (types 1–4) are identified, based on deformation features and grain size. The c-axis orientations are characterized by a single maximum near the stretching lineation and two maxima in type 1 microstructure, and by an asymmetrical, single girdle in type 2 microstructure. Quartz c axes show crossed-girdle pattern in type 3 microstructure. Both quartz microstructures and c-axis preferred orientations suggest that crystal–plastic slip and dynamic recrystallization are the dominant deformation mechanisms. The asymmetry of c-axis orientations with respect to the mylonitic foliation, as well as the substructures developed in quartz, indicates a dextral sense of shear in the Morin shear zone. Type 4 microstructure, which developed in some gneisses and granulites, is interpreted to record influence of postdeformation annealing by which quartz c-axis orientations were partially modified. In the north-northeast-trending, subvertical Labelle shear zone that separates the Morin terrane from the Mont-Laurier terrane, metamorphic assemblages and structural elements suggest that an early, sinistral strike-slip deformation occurred under granulite-facies conditions. This was overprinted by a late downdip movement of the Mont-Laurier terrane under retrogressive conditions. Quartz in felsic gneisses from this zone shows two types of microstructures: one is similar to type 4 from the Morin shear zone, the other is named type 5. Quartz c-axis orientations are complex and less systematic, due to overprinting by two episodes of deformation and possible annealing. These complexities limit the utility of quartz microstructures and c-axis data in the structural analysis of the Labelle shear zone.

Structural testing of tectonic hypotheses by field-based analysis of distributed tangential shear: examples from major high-strain zones in the Grenville Province and other parts of the southern Canadian Shield

2005 ◽  
Vol 42 (10) ◽  
pp. 1927-1947 ◽  
Author(s):  
W M Schwerdtner ◽  
U P Riller ◽  
A Borowik
Keyword(s):  
Shear Zone ◽  
High Strain ◽  
Shear Zones ◽  
Canadian Shield ◽  
Structural Testing ◽  
Grenville Province ◽  
Shallow Subsurface ◽  
Geometric Conditions ◽  
Actual Direction ◽  
Dip Angle

The Grenville Province and other parts of the Canadian Shield contain major (>100 km long) high-strain zones, also called shear belts or ductile shear zones, that are hosted by heterogeneously deformed gneisses and schists. In well-exposed segments of three nontabular zones whose dip angle is known locally, at the erosion level and (or) in the shallow subsurface, we investigate the tangential shear strain (better called the tangential unit shear or TUS) without assuming that mineral-shape lineations, common varieties of stretching lineations, are effectively parallel to the local TUS direction. Employing a graphic technique that copes with the geometric conditions of general triaxial strain, we approximate the actual direction and find the sense of local TUS in parts of (i) the Parry Sound shear zone, Grenville Province; (ii) the South Range shear zone, Southern Province; and (iii) the Uchi – English River subprovince boundary zone, Superior Province. Information thus obtained for individual high-strain zones in Ontario confirms the validity of published hypotheses: (i) 1020–970 Ma, normal-sense distributed shearing in the Grenvillian thrust stack; (ii) northwest- directed thrusting of Huronian rocks over Archean basement; and (iii) north-directed thrusting of English River metasediments and associated migmatites onto the Uchi granite–greenstone terrain, under peak metamorphic conditions.

Generation and interpretation of geophysical images with examples from the Rae Province, northwestern Canada shield

Geophysics ◽  
1990 ◽  
Vol 55 (8) ◽  
pp. 977-997 ◽  
Author(s):  
H. John Broome
Keyword(s):  
Gamma Ray ◽  
Shear Zones ◽  
Gamma Ray Spectrometry ◽  
Data Sets ◽  
Aeromagnetic Data ◽  
Different Types ◽  
Geologic Maps ◽  
Vertical Gravity ◽  
Shaded Relief ◽  
Radiometric Data

Different types of images generated from gravity, magnetic, and gamma ray spectrometry data from the Rae Province of the Canadian shield were compared with each other and geologic maps to evaluate their effectiveness for displaying the geologically relevant content of the data sets. Shading methods were useful for enhancing weak directional anomalies in the aeromagnetic data. Multi‐directional, shaded‐relief images produced by overlaying three colored, shaded‐relief images are useful for analysis of anomalies associated with structure. Vertical gravity derivative images display a continuous gravity feature linking the Wager Bay and Amer Lake shear zones that is obscured on the Bouguer gravity intensity image. Detailed vertical magnetic derivative images of the shear zone clearly displayed anomalies associated with the internal structure. Composite images generated using three different geophysical parameters show correlations between the magnetic, gravity, and radiometric data which can be related to the geology. Subtle variations in uranium, thorium, and potassium concentrations determined by gamma ray spectrometry can be effectively displayed using ternary radioelement images

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