Geon 12 crustal extension in the central Grenville Province, implications for the orogenic architecture, and potential influence on the emplacement of anorthosites

2013 ◽  
Vol 50 (9) ◽  
pp. 955-966 ◽  
Author(s):  
Aphrodite Indares ◽  
Abdelali Moukhsil
Keyword(s):  
Close Association ◽  
Volcanic Belt ◽  
Granulite Facies ◽  
Mafic Rock ◽  
Crustal Extension ◽  
Potential Influence ◽  
Grenville Province ◽  
Show Evidence ◽  
Grenvillian Orogeny ◽  
First Time

Remnants of a ca. 1.24 Ga old volcanic belt formed in a within-plate setting (Manicouagan Crustal Extension Belt) are exposed over several tens of kilometres in the hinterland of the central Grenville Province, and can be recognized despite granulite-facies Grenvillian metamorphism and deformation. This belt mainly consists of layered felsic–mafic rock units, some of which are documented here for the first time. In the vicinity of the 1.24 Ga belt, a Geon 14 arc-related mafic suite and a Geon 15 metasedimentary package were pervasively injected by felsic (and mafic) material, show evidence of a Geon 12 thermal event, and therefore may represent remnants of rifted crust. Following Geon 12 crustal extension, lithospheric-scale magmatic activity in the immediate region continued intermittently, producing mafic dykes at 1.17 Ga and anorthosite at 1.16 and 1.05 Ga. A close association to 1.16 Ga or younger anorthosite is conspicuous to several Geon 12 rock units known in the central and eastern Grenville Province. We therefore suggest that subsequent anorthositic magmatism was focused on zones of lithospheric weakness inherited from Geon 12 crustal extension and remained active intermittently until the end of the Grenvillian orogeny.

A Discussion on global tectonics in Proterozoic times - The Grenville Province in Helikian times: a possible model of evolution

1976 ◽  
Vol 280 (1298) ◽  
pp. 499-515 ◽  
Keyword(s):  
Continental Crust ◽  
Granulite Facies ◽  
Continental Collision ◽  
Canadian Shield ◽  
Grenville Province ◽  
East Central ◽  
Metasedimentary Rocks ◽  
Grenvillian Orogeny ◽  
Triangular Area ◽  
Global Tectonics

It is suggested that the Helikian (1650-1000 million years (Ma) ago) evolution of the Grenville Province in the Canadian Shield was marked by three events: emplacement of anorthosites around 1450-1500 Ma ago, rifting associated with opening of a proto-Atlantic ocean between 1200 and 1300 Ma ago, and continental collision responsible for the Grenvillian ‘orogeny’ about 1100-1000 Ma ago. Emplacement of rocks of the anorthosite suite (anorthosites and adamellites or mangerites) into continental crust was accompanied by formation of aureoles in the granulite facies. The Grenville Group was deposited in the southern part of the Province between 1300 and 1200 Ma ago and comprises marbles, clastic metasedimentary rocks and volcanics. It occupies a roughly triangular area limited on the northwest by the Bancroft—Renfrew lineament and on the southeast by the Chibougamau—Gatineau lineament. It is thought to have been accumulated in an aulacogen that would have developed along a fracture zone separating two basement blocks. The Grenvillian thermotectonic event may represent a Tibetan continental collision in the sense of Burke & Dewey. The suture zone would now be hidden under the Appalachians. Collision would cause reactivation of continental crust and renewed movement on pre-existing lineaments. The east—central part of the Grenville Province appears to have been more intensively reactivated than the western part.

Mafic and ultrapotassic rocks from the Canyon domain (central Grenville Province): geochemistry and tectonic implications

2012 ◽  
Vol 49 (2) ◽  
pp. 412-433 ◽  
Author(s):  
Carolina Valverde Cardenas ◽  
Aphrodite Indares ◽  
George Jenner
Keyword(s):  
Tectonic Setting ◽  
Source Region ◽  
Crustal Contamination ◽  
Granulite Facies ◽  
Grenville Province ◽  
Mafic Rocks ◽  
Isotopic Signatures ◽  
Late Evolution ◽  
Grenvillian Orogeny ◽  
Laurentian Margin

The Canyon domain and the Banded complex in the Manicouagan area of the Grenville Province preserve a record of magmatic activity from ∼1.4 to 1 Ga. This study focuses on 1.4–1.2 Ga mafic rocks and 1 Ga ultrapotassic dykes. Geochemistry and Sm–Nd isotopic signatures were used to constrain the origin of these rocks and evaluate the changing role of the mantle with time and tectonic setting from the late evolution of the Laurentian margin to the Grenvillian orogeny, in the Manicouagan area. The mafic rocks include layers inferred to represent flows, homogeneous bodies in mafic migmatite, and deformed dykes, all of which were recrystallized under granulite-facies conditions during the Grenvillian orogeny. In spite of the complexities inherent in these deformed and metamorphosed mafic rocks, we were able to recognize suites with distinctive geochemical and isotopic signatures. Integration of this data along with available ages is consistent with a 1.4 Ga continental arc cut by 1.2 Ga non-arc basalts derived from depleted asthenospheric mantle, with varied degrees of crustal contamination and inferred to represent magmatism in an extensional environment. The 1 Ga ultrapotassic dykes postdate the Grenvillian metamorphism. They are extremely enriched in incompatible elements, have negative Nb anomalies, relatively unradiogenic Sr-isotopic compositions (initial 87Sr/86Sr ~ 0.7040) and εNd –3 to –15. Some dykes have compositional characteristics consistent with derivation from the mantle, ruling out crustal contamination as a major process in their petrogenesis. The most likely source region for the ultrapotassic dykes is a metasomatized subcontinental lithospheric mantle, with thermal input from the asthenosphere in association with post-orogenic delamination.

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.

Metamorphic constraints on the evolution of the gneisses from the parautochthonous and allochthonous polycyclic belts, Grenville Province, western Quebec

1990 ◽  
Vol 27 (3) ◽  
pp. 357-370 ◽  
Author(s):  
A. Indares ◽  
J. Martignole
Keyword(s):  
Granulite Facies ◽  
Ultramafic Rocks ◽  
Significant Discrepancy ◽  
Grenville Province ◽  
Narrow Strip ◽  
Metasedimentary Rocks ◽  
Metamorphic History ◽  
Tectonic Transport ◽  
History Of ◽  
Grenvillian Orogeny

The tectono-metamorphic history of polycyclic "grey gneisses" located in the central Grenville Province of western Quebec has been constrained along a transect perpendicular to the length of the Grenville Orogen. Two terranes, the Réservoir Dozois terrane (RDT) and the Réservoir Baskatong terrane (RBT), were recognized from their structural, lithological, and geochronological characteristics. This subdivision has been confirmed by application of geothermobarometric techniques to appropriate mineral assemblages.The RDT is the southern extension of the parautochthonous belt of the Grenville Province, which in this area is composed of Archean rocks of upper-amphibolite grade. During the Grenvillian Orogeny, northwest-directed thrusting resulted in the tectonic burial of this terrane as a single tectonic unit, in contrast with the northern part of the parautochthonous belt, where several slices were imbricated against the Grenville Front. Maximum P–T conditions in the RDT (850 MPa, 720 °C) were likely Grenvillian and were followed by pervasive retrogression down to the hornblende–epidote subfacies. Locally, the RDT is overlain by remnants of thrust slices composed of monocyclic metasedimentary rocks that were deformed and metamorphosed in the granulite facies during the Grenvillian Orogeny.To the southeast, the RBT is an allochthonous or exotic terrane probably of Proterozoic age. It also experienced tectonic burial by thrusting (1030 MPa, 710 °C) during the Grenvillian Orogeny, whose thermal climax (790 °C) coincided with charnockite emplacement during decompression to 850 MPa.These two terranes are separated by a narrow strip of sheared rocks, the Renzy shear belt (RSB), which comprises mafic and ultramafic rocks subjected to high P and T (975 MPa, 745 °C). In view of the significant discrepancy between the metamorphic histories of the two terranes separated by the RSB, major tectonic transport has to be envisaged along this zone.

Pre-Kenoran Tonalitic Gneisses in the Grenville Province

1975 ◽  
Vol 12 (5) ◽  
pp. 844-849 ◽  
Author(s):  
R. A. Frith ◽  
R. Doig
Keyword(s):  
Granulite Facies ◽  
Retrograde Metamorphism ◽  
Initial Ratio ◽  
Fold Belt ◽  
Grenville Province ◽  
Tonalitic Gneiss ◽  
Grenvillian Orogeny

Rb–Sr whole-rock studies of tonalitic gneiss within the Grenville Province on the eastern extension of the Abitibi fold belt may indicate an age greater than 3000 m.y. The gneiss samples were collected up to 32 miles (52 km) from the Grenville Front. Rocks beyond this generally show the effects of the Grenvillian orogeny about 1100 m.y. ago which raised the 87Rb/86Sr initial ratio from about 0.7025 to 0.7148. Rocks more than 40 miles (64 km) from the Grenville Front show retrograde metamorphism from the granulite facies that is considered to be related to the metamorphism associated with the intrusion of anorthosite still farther to the southeast (ca. 1500 m.y.). The Archean tonalitic gneisses exhibit E–W and NE–SW aeromagnetic trends but similar rocks to the southeast exhibit aeromagnetic patterns that are chiefly N–S and may be a result of Hudsonian deformation. A small granitic body in this zone of N–S aeromagnetic pattern was intruded 1745 ± 23 m.y. ago(87Rb λ = 1.39 × 10−11y−1).

Geology and age of the Precambrian basement in the Windsor, Chatham, and Sarnia area, southwestern Ontario

1982 ◽  
Vol 19 (8) ◽  
pp. 1627-1634 ◽  
Author(s):  
A. Turek ◽  
R. N. Robinson
Keyword(s):  
Oil And Gas ◽  
Precambrian Basement ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Gas Drilling ◽  
Arch System ◽  
Grenvillian Orogeny ◽  
Anomaly Map ◽  
Paleozoic Rocks ◽  
Basement Surface

Precambrian basement in the Windsor–Chatham–Sarnia area is covered by Paleozoic rocks that are up to 1300 m thick. The basement surface is characterized by a northeast–southwest arch system with a relief of about 350 m. Extensive oil and gas drilling has penetrated and sampled this basement, and an examination of core and chip samples from 133 holes and an assessment of the magnetic anomaly map of the area have been used to produce a lithologic map of the Precambrian basement. The predominant rocks are granite gneisses and syenite gneisses but also significant are gabbros, granodiorite gneisses, and metasedimentary rocks. The average foliation dips 50° and is inferred to have a northeasterly trend. The Precambrian basement has been regarded as part of the Grenville Province. An apparent Rb–Sr whole rock isochron, for predominantly meta-igneous rocks, yields an age of 1560 ± 140 Ma. This we interpret as pre-Grenvillian, surviving the later imprint of the Grenvillian Orogeny. Points excluded from the isochron register ages of 1830, 915, and 670 Ma, and can be interpreted as geologically meaningful.

scholarly journals The 31 March 2020 Mw 6.5 Stanley, Idaho, Earthquake: Seismotectonics and Preliminary Aftershock Analysis

2020 ◽  
Author(s):  
Lee M. Liberty ◽  
Zachery M. Lifton ◽  
T. Dylan Mikesell
Keyword(s):  
Surface Displacement ◽  
Volcanic Belt ◽  
Normal Fault ◽  
Fault System ◽  
Basin And Range Province ◽  
Ground Shaking ◽  
The North ◽  
Show Evidence ◽  
Tectonic Framework ◽  
Tectonic Belt

Abstract We report on the tectonic framework, seismicity, and aftershock monitoring efforts related to the 31 March 2020 Mw 6.5 Stanley, Idaho, earthquake. The earthquake sequence has produced both strike-slip and dip-slip motion, with minimal surface displacement or damage. The earthquake occurred at the northern limits of the Sawtooth normal fault. This fault separates the Centennial tectonic belt, a zone of active seismicity within the Basin and Range Province, from the Idaho batholith to the west and Challis volcanic belt to the north and east. We show evidence for a potential kinematic link between the northeast-dipping Sawtooth fault and the southwest-dipping Lost River fault. These opposing faults have recorded four of the five M≥6 Idaho earthquakes from the past 76 yr, including 1983 Mw 6.9 Borah Peak and the 1944 M 6.1 and 1945 M 6.0 Seafoam earthquakes. Geological and geophysical data point to possible fault boundary segments driven by pre-existing geologic structures. We suggest that the limits of both the Sawtooth and Lost River faults extend north beyond their mapped extent, are influenced by the relic trans-Challis fault system, and that seismicity within this region will likely continue for the coming years. Ongoing seismic monitoring efforts will lead to an improved understanding of ground shaking potential and active fault characteristics.

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.

Euphausiids in the Coral and Tasman Seas during May 1972, I. Horizontal and Vertical Distribution

1979 ◽  
Vol 30 (5) ◽  
pp. 551 ◽  
Author(s):  
FB Griffiths
Keyword(s):  
Mouth Opening ◽  
Migration Pattern ◽  
Night Time ◽  
Migration Patterns ◽  
Diel Migration ◽  
Show Evidence ◽  
The Mean ◽  
Time Periods ◽  
First Time ◽  
Horizontal And Vertical Distribution

Thirty-three species belonging to seven genera of euphausiids were collected at two stations, 20� S.,153� E. and 33� 40'S.,153� E., during May 1972 off the east Australian coast. In all, 33 hauls at the northern station and 21 at the southern station were made with a mouth-opening-losing Tucker trawl at various depths between the surface and 400 m. The hauls were grouped into four time periods: dawn (0401-1000 h), noon (1001-1600 h), dusk (1601-2000 h) and midnight (2001-0400 h). The mean number of euphausiids of all species was 20.78 per 1000 m³ at 33� 40's. and 18.34 per 1000 m³ at 20%. Night-time abundances were greater than day-time abundances at both stations. Twenty-five species were found at the northern station and 29 species at the southern station. Four species, Thysanopoda astylata, T. obtusifrons, T. monacantha, and Nernatoscelis atlantica, were found only at the northern station and eight species, Thysanopoda acutifrons, T. orientalis, Pseudeuphausia latifrons, Euphausia recurva, E. pseudogibba, E. similis variety armata, E. spinifera, and Nematoscelis megalops were found only at the southern station. Euphausia similis is reported from 20� CS..153� E. for the first time. The abundance of 14 species was large enough to allow examination of their diel migration patterns. Only one, Stylocheiron abbreviatum; did not show evidence of a diurnal migration pattern. Thysanoesa gregaria exhibited a probable reversed-migration pattern.

Revision of the Genus Metaselena Diakonoff (Lepidoptera:Tortricidae)

1981 ◽  
Vol 29 (2) ◽  
pp. 233 ◽  
Author(s):  
M Horak ◽  
W Sauter
Keyword(s):  
New Species ◽  
Male Genitalia ◽  
Close Association ◽  
New Guinea ◽  
Systematic Position ◽  
First Time

The male genitalia of the genus Metaselena Diak. are described and illustrated for the first time, and as a result of that the genus is transferred to the Olethreutinae. Eight new species of Metaselena - lepta, rhabdota, symphylos, pemphigodes, pithana, platyptera, diakonoffi and allophlebodes - are described and illustrated. The systematic position of Metaselena, so far known only from Australia and New Guinea, is briefly discussed and the close association of the genus with Eucosmomorpha Obr. is pointed out.

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