Horizontal contraction or horizontal extension? Heterogeneous Late Eocene and Early Oligocene general shearing during blueschist and greenschist facies metamorphism at the Pennine–Austroalpine boundary zone in the Western Alps

1995 ◽  
Vol 84 (4) ◽  
pp. 843 ◽  
Author(s):  
U. Ring
Keyword(s):  
Western Alps ◽  
Late Eocene ◽  
Greenschist Facies ◽  
Boundary Zone ◽  
Early Oligocene ◽  
Facies Metamorphism ◽  
Greenschist Facies Metamorphism

The Gran San Bernardo nappe in the Aosta valley (western Alps): a composite stack of distinct continental crust units

2005 ◽  
Vol 176 (5) ◽  
pp. 417-431 ◽  
Author(s):  
Marco G. Malusà ◽  
Riccardo Polino ◽  
Silvana Martin
Keyword(s):  
Shear Zones ◽  
Western Alps ◽  
Greenschist Facies ◽  
Deformation History ◽  
Metamorphic Overprint ◽  
Middle Cambrian ◽  
Facies Metamorphism ◽  
Granitoid Rocks ◽  
Late Stages ◽  
Greenschist Facies Metamorphism

Abstract In the Aosta Valley, the Gran San Bernardo nappe, which comprises the basement sequences classically referred to as Ruitor Massif and Zona Interna, appears to be a stack of distinct basement units with distinct lithological features and contrasting tectono-metamorphic evolution piled up during the Eocene. In the former Zona Interna, two different units (Gran Nomenon and Leverogne) have been distinguished. The Gran Nomenon unit is a polymetamorphic basement unit, with a pre-Alpine epidote-amphibolite facies metamorphic imprint, intruded by granitoid rocks during the early Mississippian. It bears the evidence of a pervasive Alpine metamorphic overprint under greenschist facies conditions, and does not share common characters with any other basement sequence exposed in the Gran San Bernardo nappe. The Leverogne unit is a monometamorphic basement unit, with some analogies with the Mont Pourri basement sequence, intruded by granophyric rocks of Middle Cambrian age. It suffered epidote-blueschist and greenschist facies metamorphism during the Alpine orogenesis, and shows a deformation history partly different with respect to the Gran Nomenon unit. These units are bounded by tectonic melanges that represent Alpine shear zones, and have been juxtaposed under greenschist facies conditions during the late stages of exhumation of the belt. The Gran Nomenon unit, which does not show a significant HP/LT overprint, was probably not as deeply buried as the Leverogne and the Ruitor units during Alpine orogenesis.

Fluid migration and vein formation during deformation and greenschist facies metamorphism at Ormiston Gorge, central Australia

1994 ◽  
Vol 12 (4) ◽  
pp. 373-386 ◽  
Author(s):  
I. CARTWRIGHT ◽  
W. L. POWER ◽  
N. H. S. OLIVER ◽  
R. K. VALENTA ◽  
G. S. MCLATCHIE
Keyword(s):  
Greenschist Facies ◽  
Fluid Migration ◽  
Vein Formation ◽  
Facies Metamorphism ◽  
Central Australia ◽  
Greenschist Facies Metamorphism

Does piemontite represent only greenschist facies metamorphism?

1973 ◽  
Vol 40 (1) ◽  
pp. 79-82 ◽  
Author(s):  
Howard L. Stensrud
Keyword(s):  
Greenschist Facies ◽  
Facies Metamorphism ◽  
Greenschist Facies Metamorphism

Amphibolite and blueschist-greenschist facies metamorphism, Blue Mountain inlier, eastern Jamaica

2008 ◽  
Vol 43 (5) ◽  
pp. 525-541 ◽  
Author(s):  
Richard N. Abbott ◽  
Betsy R. Bandy
Keyword(s):  
Greenschist Facies ◽  
Blue Mountain ◽  
Facies Metamorphism ◽  
Greenschist Facies Metamorphism

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.

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.

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.

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