Crossitic amphibole and its possible tectonic significance in the Richmond Area, southeastern Quebec

1976 ◽  
Vol 13 (5) ◽  
pp. 711-714 ◽  
Author(s):  
W. E. Trzcienski Jr.
Keyword(s):  
Subduction Zone ◽  
Geophysical Data ◽  
Greenschist Facies ◽  
The South ◽  
Tectonic Significance ◽  
Facies Metamorphism ◽  
Greenschist Facies Metamorphism

Crossitic amphibole suggesting blueschist-type metamorphism has been found in the Richmond area, southeastern Quebec. Prehnite facies metamorphism to the northeast of Richmond and greenschist facies metamorphism to the south along with the blueschist-type metamorphism and geophysical data suggest that the Richmond area may represent a partially eroded Ordovician subduction zone.

scholarly journals The tectono-metamorphic evolution of a dismembered ophiolite (Tinos, Cyclades, Greece)

1996 ◽  
Vol 133 (3) ◽  
pp. 237-254 ◽  
Author(s):  
Yaron Katzir ◽  
Alan Matthews ◽  
Zvi Garfunkel ◽  
Manfred Schliestedt ◽  
Dov Avigad
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Subduction Zone ◽  
Sea Water ◽  
Regional Metamorphism ◽  
Greenschist Facies ◽  
Normal Faults ◽  
Model Calculations ◽  
Facies Metamorphism ◽  
Greenschist Facies Metamorphism

AbstractThe six exposures of the Upper tectonic Unit of the Cycladic Massif occurring on the island of Tinos are shown to comprise a metamorphosed dismembered ophiolite complex. The common stratigraphic section consisting of tens-of-metres- thick tectonic slices of mafic phyllites overlain by serpentinites and gabbros is considered to have been derived by a combination of thrusting during obduction and subsequent attenuation by low-angle normal faults. All rock types show evidence of a phase of regional greenschist-facies metamorphism, which in the case of the phyllites is accompanied by penetrative deformation. The greenschist-facies metamorphism in gabbros is preceded by high temperature sea-floor amphibolite-facies alteration, whereas in the serpentinites, the antigorite + forsterite greenschist-facies assemblage overprinted an earlier low temperature lizardite serpentinite. Trace element patterns of the mafic phyllites and a harzburgitic origin of meta-serpentinites suggest a supra subduction zone (SSZ) affinity for the ophiolitic suite. ρ18O values of phyllites, gabbros and serpentinites range from 6 to 15%o. Model calculations indicate that such values are consistent with low temperature (50–200°C) alteration of parent rocks by sea-water at varying water/rock ratios. This would agree with the early low temperature mineralogy of the serpentinites, but the early high temperature alteration of the gabbros would require the presence of 18O-enriched sea-water.The following overall history is suggested for Tinos ophiolitic slices. (1) Oceanic crust was generated at a supra-subduction zone spreading centre with high temperature alteration of gabbros. (2) Tectonic disturbance (its early hot stages recorded in an amphibolitic shear zone at the base of serpentinites) brought the already cooled ultramafics into direct contact with sea-water and caused low-T serpentinization. (3) Tectonism after cooling involved thrusting which caused repetition and inversion of the original order of the oceanic suite. (4) Regional metamorphism of all the ophiolite components at greenschist-facies conditions (−450°C) overprinted the early alteration mineralogy. It was probably induced by continued thrusting and piling up of nappes. The Tinos ophiolite, dated as late Cretaceous and genetically related to other low pressure rock-units of the same age in the Aegean, differs in age and degree of dismemberment and metamorphism from ophiolites in mainland Greece.

The Age of the Sudbury Nickel Irruptive and the Murray Granite

1975 ◽  
Vol 12 (12) ◽  
pp. 1970-1989 ◽  
Author(s):  
Walter A. Gibbins ◽  
R. H. McNutt
Keyword(s):  
Shock Metamorphism ◽  
Greenschist Facies ◽  
The South ◽  
Rock Samples ◽  
The North ◽  
Facies Metamorphism ◽  
North And South ◽  
Granite Samples ◽  
Greenschist Facies Metamorphism

Whole-rock samples of norite from the North and South Ranges of the Sudbury Irruptive yield a rubidium strontium isochron of 1956 ± 98 Ma age and (87Sr/86Sr)o = 0.7063 (λ87Rb = 1.39 × 10−11 a−1). Five samples of ore bearing 'sub-layer' from the South Range are compatible with this age. Four new determinations of South Range and six published analyses of North Range micropegmatite define an isochron of age = 1680 ± 30 Ma with (87Sr/86Sr)o = 0.708.The norite age is believed to represent the 'Sudbury event', a local event marked by the development of shock metamorphism and intrusion of the nickel irruptive. The 1680 Ma micropegmatite age is believed to be secondary and related to greenschist-facies metamorphism in the center of the Sudbury Basin during the Penokean Orogeny. Evidence supporting a later separate intrusion of granophyre-rich micropegmatite suggests that the time of this intrusion was relatively soon after the norite rather than 1680 Ma ago.Analyses of Murray granite samples indicate a pre-norite age of 2260 Ma. Most of the Murray granite shows evidence of later metamorphic events including the Sudbury event. Late (post-norite and post-Murray granite) granitic dikes (i.e., the Murray offshoots) intrude the norite near the Murray granite. These and other smaller granitic dikes appear to have formed 1700 to 1800 Ma ago. The origin of these dikes remains problematical.

scholarly journals Thermochronological evidence for late Proterozoic (Vendian) cooling in southwest Wedel Jarlsberg Land, Spitsbergen

1998 ◽  
Vol 135 (1) ◽  
pp. 63-69 ◽  
Author(s):  
M. MANECKI ◽  
D. K. HOLM ◽  
J. CZERNY ◽  
D. LUX
Keyword(s):  
Geological Mapping ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Variable Intensity ◽  
Late Proterozoic ◽  
Facies Metamorphism ◽  
History Of ◽  
Greenschist Facies Metamorphism

Two Proterozoic terranes with different metamorphic histories are distinguished from geological mapping in southwestern Wedel Jarlsberg Land: a northern greenschist facies terrane and a southern amphibolite facies terrane which has been overprinted by greenschist facies metamorphism. To better characterize the tectonothermal history of these terranes we have obtained new 40Ar/39Ar mineral dates from this area. A muscovite separate from the northern terrane yielded a Caledonian plateau age of 432±7 Ma. The southern terrane yielded significantly older 40Ar/39Ar ages with three muscovite plateau dates of 584±14 Ma, 575±15 Ma, and 459±9 Ma, a 484±5 Ma biotite plateau date, and a 616±17 Ma hornblende plateau date. The oldest thermochronological dates are over 300 Ma younger than the age of amphibolite facies metamorphism and therefore probably do not represent uplift-related cooling. Instead, the Vendian dates correlate well with a regionally widespread magmatic and metamorphic/thermal resetting event recognized within Caledonian complexes of northwestern Spitsbergen and Nordaustlandet. The apparent Ordovician dates are interpreted to represent partial resetting, suggesting that late Caledonian greenschist facies overprinting of the southern terrane was of variable intensity.

scholarly journals Tectonic Fabric, Geochemistry, and Zircon-Monazite Geochronology as Proxies to Date an Orogeny: Example of South Delhi Orogeny, NW India, and Implications for East Gondwana Tectonics

2021 ◽  
Vol 8 ◽  
Author(s):  
Subhash Singh ◽  
Bert De Waele ◽  
Anjali Shukla ◽  
B. H. Umasankar ◽  
Tapas Kumar Biswal
Keyword(s):  
Large Scale ◽  
Greenschist Facies ◽  
Passive Margin ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Mobile Belt ◽  
Brittle Deformation ◽  
The South ◽  
Rock Types ◽  
Greenschist Facies Metamorphism

We have dated the South Delhi orogeny, Aravalli-Delhi Mobile Belt (ADMB), NW India, using the tectonic fabric, geochemistry, and zircon-monazite geochronology as the proxies. The South Delhi Terrane (SDT), a passive margin domain in the ADMB, consists of multiply deformed (D1–D4) greenschist facies rocks and several granite plutons. The D1 deformation is characterized by pervasive isoclinal recumbent F1 fold and axial planar tectonometamorphic fabric, S1, developed in all rock types. The S1 minerals belong to peak greenschist facies metamorphism, M1, suggesting syntectonic nature of M1 with D1. The age of the D1-M1 is constrained by the syncollisional peralkaline S type Sewariya granite which is characterized by magmatic/submagmatic fabric (Sm) coplanar with the S1. The margin of the pluton is turned into quartzofeldspathic gneiss carrying the evidence of high temperature deformation. The age of Sewariya granite is estimated at ca. 878 Ma by zircon geochronology. The D1-M1 is further constrained by monazite geochronology of the mica schist at ca. 865–846 Ma. The other granite plutons and metarhyolite are pre-D1 and emplaced at ca. 992–946 Ma. The D2 deformation produced NE-SW trending open upright F2 folds coaxial with the F1, and northwesterly vergent F2–axial planar thrusts. Monazite geochronology constrains the D2 at ca. 811–680 Ma. The D3 is characterized by small to large scale NW-SE folds, and the D4 by faults and fractures marking the brittle deformation in the rocks. The D4 is constrained by monazite geochronology at ca. 588–564 Ma. There are upper amphibolitic tectonic slivers along the D2-Phulad thrust, belonging to the pre-Delhi rocks, which show ca. 1,638 Ma metamorphism age. From the above study, it is suggested that the South Delhi orogeny belongs to ca. 878–680 Ma marking the final amalgamation of Marwar Craton with the rest of India. This overlaps the early phase of the Pan-African orogeny (900–630 Ma). The brittle deformation, D4, coincides with Kuunga orogeny (650–500 Ma). Our study implies that India, like other continents in the East Gondwana, underwent amalgamation of internal blocks until the late part of the Neoproterozoic.

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