U – Pb age constraints for the lithotectonic evolution of the Grenville Province along the Mauricie transect, Quebec

1997 ◽  
Vol 34 (3) ◽  
pp. 299-316 ◽  
Author(s):  
David Corrigan ◽  
Otto van Breemen
Keyword(s):  
Shear Zone ◽  
Tectonic Evolution ◽  
High Grade ◽  
Isotopic Age ◽  
Grenville Province ◽  
Zircon Age ◽  
South Central ◽  
Continental Arc ◽  
Structural Levels ◽  
Age Constraints

New U–Pb zircon and monazite ages on 12 samples from the Mauricie transect in Quebec provide constraints on the lithologic and tectonic evolution of the south-central Grenville Province. From lowest to highest structural levels, the Mékinac, Shawinigan, and Portneuf – St. Maurice domains are identified on the basis of protolith age, tectonic overprint, and plutonism. The structurally highest Portneuf – St. Maurice domain consists of remnants of an island arc (Montauban Group) that was deformed and metamorphosed before and during the intrusion of continental arc plutons (La Bostonnais complex). A tonalitic orthogneiss yielding a [Formula: see text] zircon age suggests that most of the structurally underlying Mékinac and Shawinigan domains consist of orthogneisses that may be high-grade equivalents of the La Bostonnais complex. A voluminous metasedimentary unit occurring in the Shawinigan domain (St. Boniface unit) was deposited between ca. 1.18 and 1.09 Ga, precluding any correlation with the ca. 1.45 Ga Montauban Group. Two suites of anorthosite–mangerite–charnockite–granite (AMCG) plutonic rocks are identified on the basis of field relationships and isotopic age. A megacrystic granite belonging to the "older" AMCG suite yielded a [Formula: see text] zircon age. Three plutons from the "younger" suite yielded ages of [Formula: see text], 1059 ± 2, and 1056 ± 2 Ma. The Mékinac and Shawinigan domains, excluding the younger AMCG plutons, were penetratively deformed at granulite to uppermost amphibolite facies during west-northwest-directed thrusting between 1.15 and 1.09 Ga. At ca. 1.09 Ga, a transition from contraction to oblique extension resulted in the juxtaposition of the "cold" Portneuf – St. Maurice domain with the "hot" Shawinigan domain, along the Tawachiche shear zone. Oblique extension may have been active from ca. 1.09 to 1.04 Ga and was contemporaneous with emplacement of the younger AMCG suite.

New age constraints on magmatism and metamorphism in the Morin terrane (Grenville Province, Quebec)

2022 ◽  
Author(s):  
William H Peck ◽  
Matthew P Quinan
Keyword(s):  
Shear Zone ◽  
Granulite Facies ◽  
Western Boundary ◽  
Grenville Province ◽  
Granulite Facies Metamorphism ◽  
Metamorphic History ◽  
Crustal Block ◽  
Two Samples ◽  
Western Side ◽  
Age Constraints

The Morin terrane is an allochthonous crustal block in the southwestern Grenville Province with a relatively poorly-constrained metamorphic history. In this part of the Grenville Province, some terranes were part of the ductile middle crust during the 1.09–1.02 Ga collision of Laurentia with the Amazon craton (the Ottawan phase of the Grenvillian orogeny), while other terranes were part of the orogen’s superstructure. New U-Pb geochronology suggests that the Morin terrane experienced granulite-facies metamorphism during the accretionary Shawinigan orogeny (1.19–1.14 Ga) and again during the Ottawan. Seven zircon samples from the 1.15 Ga Morin anorthosite suite were dated to confirm earlier age determinations, and Ottawan metamorphic rims (1.08–1.07 Ga) were observed in two samples. U-Pb dating of titanite in nine marble samples surrounding the Morin anorthosite suite yielded mixed ages spanning between the Shawinigan and Ottawan metamorphisms (n=7), and predominantly Ottawan ages (n=2). Our results show that Ottawan zircon growth and resetting of titanite ages is spatially heterogeneous in the Morin terrane. Ages with a predominantly Ottawan signature are recognized in the Morin shear zone, which deforms the eastern lobe of the anorthosite, in an overprinted skarn zone on the western side of the massif, and in the Labelle shear zone that marks its western boundary. In the rest of the Morin terrane titanite with Shawinigan ages appear to have been only partially reset during the Ottawan. Further work is needed to better understand the relationship between the character of Ottawan metamorphism and resetting in different parts of the Morin terrane.

40Ar/39Ar and K–Ar age constraints on shear zone evolution, southern Taltson magmatic zone, northeastern Alberta

1995 ◽  
Vol 32 (3) ◽  
pp. 281-291 ◽  
Author(s):  
H. E. Plint ◽  
M. R. McDonough
Keyword(s):  
Cooling Rate ◽  
Shear Zone ◽  
High Grade ◽  
Slow Cooling ◽  
Rapid Cooling ◽  
Deformational History ◽  
The Mean ◽  
Exhumation Rates ◽  
Northeastern Alberta ◽  
Age Constraints

New 40Ar/39Ar analyses of hornblende, muscovite, biotite, and K-feldspar constrain the timing of deformation and cooling of the southern Taltson magmatic zone, which underwent lower granulite to upper amphibolite grade deformation, in part synchronous with voluminous 1.99–1.92 Ga magmatism. New data are combined with existing K–Ar dates into a regional cooling framework to provide thermotemporal constraints on the deformational history. 40Ar/39Ar hornblende ages of ca. 1900 Ma are interpreted to record relatively rapid cooling following ductile thrusting on the Andrew Lake shear zone, and younger anatectic magmatism. These data, with published K–Ar and U–Pb data, support relatively rapid cooling of the Taltson magmatic zone from monazite closure temperature of 725 °C at ca. 1930 Ma to 525 °C at ca. 1900 Ma. Cooling rate estimates are about 7 °C/Ma, which suggests moderate exhumation rates during the high-grade part of the deformational history. A muscovite 40Ar/39Ar plateau age of 1803 ± 11 Ma is consistent with the mean muscovite K–Ar age of 1792 Ma, indicating regional cooling through about 350 °C at ca. 1800 Ma. 40Ar/39Ar ages from magmatic biotite of 1856 and 1799 Ma also suggest slow cooling during greenschist grade deformation, which can be no older than ca. 1860 Ma. A K-feldspar 40Ar/39Ar age of 1681 Ma provides a lower limit for the time of greenschist grade deformation. Cooling rate estimates during amphibolite to greenschist grade deformation are 1.75–2.25 °C/Ma.

U–Pb zircon age of the southwest lobe of the Havre-Saint-Pierre Anorthosite Complex, Grenville Province, Canada

1993 ◽  
Vol 30 (7) ◽  
pp. 1453-1457 ◽  
Author(s):  
Otto van Breemen ◽  
Michael D. Higgins
Keyword(s):  
Solid State ◽  
Shear Zone ◽  
Late Stage ◽  
Grenville Province ◽  
Zircon Age ◽  
Zircon Dating ◽  
Granitoid Intrusions ◽  
Anorthosite Complex ◽  
Massif Anorthosite ◽  
Magmatic Event

U–Pb zircon dating of the southwest lobe of the Havre-Saint-Pierre anorthosite intrusion indicates that it is 1062 ± 4 Ma old. Parallelism of magmatic and solid-state foliations with the adjacent Abbé–Huard lineament suggest that anorthosite parental magmas rose up this shear zone, which was active at that time. The age of igneous crystallization is much younger than that of a spatially associated mangerite intrusion, but accords with age data from other granitoid intrusions elsewhere in the Grenville Province. Evidence points to a widespread 1.09–1.05 Ga magmatic event that included massif anorthosite intrusions. This magmatic event coincided with late stage convergent tectonics in the southwestern Grenville Province.

40Ar/39Ar thermochronology of the Thor-Odin – Pinnacles area, southeastern British Columbia: tectonic implications of cooling and exhumation patterns

2016 ◽  
Vol 53 (10) ◽  
pp. 993-1009 ◽  
Author(s):  
D. van Rooyen ◽  
S.D. Carr
Keyword(s):  
British Columbia ◽  
Shear Zone ◽  
Late Cretaceous ◽  
Columbia River ◽  
Metamorphic Rocks ◽  
Structural Level ◽  
High Grade ◽  
Extensional Deformation ◽  
Structural Levels ◽  
Upper Boundary

The Thor-Odin dome is a basement-cored tectonothermal culmination in southern British Columbia, containing high-grade metamorphic rocks that were polydeformed during the Cordilleran orogenesis. A north–south 40Ar/39Ar thermochronology transect was carried out throughout a ∼7 km thick tilted section in the Thor-Odin dome and structurally overlying rocks to construct thermochronological histories using existing U–Pb geochronology data with new 40Ar/39Ar data and to determine the nature of the boundary between the dome and overlying rocks at Cariboo Alp. Hornblende cooling dates are ∼62–58 Ma at the highest structural level, ∼57–55 Ma in the middle, and ∼57–53 Ma at Cariboo Alp on the upper boundary of the dome. Muscovite and biotite cooling dates are ∼53–50.5 Ma; identical throughout the dome, margin, and overlying panel. The Cariboo Alp area separating the Thor-Odin dome from overlying rocks did not accommodate major post-cooling extensional deformation; rather, it is a Late Cretaceous to Paleocene compressional shear zone. These domains cooled at different rates from >700 to ca. 300 °C, with upper structural levels cooling at rates of ca. 20 °C/Ma and the lowest levels at rates in excess of 120 °C/Ma. All levels passed through the closure temperature for argon in biotite (here calculated to be 320–330 °C) together at ca. 52–51 Ma. Differential cooling rates are the result of interaction between northeast-directed compressional transport of rocks towards the foreland of the orogen overlapping with activity on the Columbia River fault zone, reflecting crustal-scale extension that reached a peak in the Eocene.

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.

U-Pb ages of plutonism, wollastonite formation, and deformation in the central part of the Lac-Saint-Jean anorthosite suite

2002 ◽  
Vol 39 (7) ◽  
pp. 1093-1105 ◽  
Author(s):  
Michael D Higgins ◽  
Mohcine Ider ◽  
Otto van Breemen
Keyword(s):  
Partial Melting ◽  
Shear Zone ◽  
Fault System ◽  
Grenville Province ◽  
Zircon Age ◽  
Thermal Event ◽  
Magmatic Event

The Lac-Saint-Jean anorthosite suite (LSJAS) is the largest ensemble of plutons in the Grenville Province. Zircons from a pluton in the central part of the LSJAS yield an age of 1140+10–5 Ma, which accords with existing 1157–1142 Ma ages determined from the southern part of the LSJAS. The Du Bras granite is a linear pluton emplaced into the dominantly dextral Pipmuacan shear zone (PSZ). The U–Pb zircon age of 1148 ± 2 Ma for the Du Bras granite confirms earlier proposals that it is a granophyre, formed at greater depths by partial melting of paragneiss by the heat of the crystallizing anorthosite. Parts of the pluton are strongly deformed by the shear zone, and other parts cut the shear zone. This suggests that the pluton dates one phase of movement of the PSZ. The Canton-St-Onge wollastonite deposit was developed in paragneisses preserved within the PSZ. Titanite from this deposit gives an age of 1163 ± 18 Ma, identical within error to that of the Du Bras granite, indicating that this pluton may have provided the skarn fluids. A second plutonic cycle comprises the post-tectonic Astra granite, which stitches the PSZ, and an amazonite-bearing pegmatite dyke. Zircons gave an age of 1028 ± 2 Ma for the Astra granite. The amazonite-bearing dyke only yielded monazite, one fraction of which gave an age similar to that of the Astra granite. Other fractions record the effects of a thermal event at 1020–1017 Ma that may be related to a widespread magmatic event. The undeformed Venus de Milot syenitic intrusion yields a U–Pb age of 988 ± 2 Ma. It was emplaced along the northwest-trending Lac Rioux fault, indicating that one phase of movement occurred before 988 Ma. Another strand of the same fault system also cuts the intrusion, showing later reactivation that may have been associated with the formation of the Saguenay Graben.

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