Geometry of eclogite-facies structural features: Implications for production and exhumation of ultrahigh-pressure and high-pressure rocks, Western Gneiss Region, Norway

Tectonics ◽  
2004 ◽  
Vol 23 (2) ◽  
pp. n/a-n/a ◽  
Author(s):  
Michael P. Terry ◽  
Peter Robinson
Keyword(s):  
High Pressure ◽  
Structural Features ◽  
Ultrahigh Pressure ◽  
Western Gneiss Region ◽  
Eclogite Facies

Pre-Caledonian granulite and gabbro enclaves in the Western Gneiss Region, Norway: indications of incomplete transition at high pressure

2000 ◽  
Vol 137 (3) ◽  
pp. 235-255 ◽  
Author(s):  
M. KRABBENDAM ◽  
A. WAIN ◽  
T. B. ANDERSEN
Keyword(s):  
High Pressure ◽  
Shear Zones ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Ultrahigh Pressure ◽  
Western Gneiss Region ◽  
Ultrahigh Pressure Metamorphism ◽  
Mountain Belts ◽  
Orogenic Cycle ◽  
Highly Strained

The Western Gneiss Region of Norway is a continental terrane that experienced Caledonian high-pressure and ultrahigh-pressure metamorphism. Most rocks in this terrane show either peak-Caledonian eclogite-facies assemblages or are highly strained and equilibrated under late-Caledonian amphibolite-facies conditions. However, three kilometre-size rock bodies (Flatraket, Ulvesund and Kråkenes) in Outer Nordfjord preserve Pre-Caledonian igneous and granulite-facies assemblages and structures. Where these assemblages are preserved, the rocks are consistently unaffected by Caledonian deformation. The three bodies experienced high-pressure conditions (20–23 kbar) but show only very localized (about 5%) eclogitization in felsic and mafic rocks, commonly related to shear zones. The preservation of Pre-Caledonian felsic and mafic igneous and granulite-facies assemblages in these bodies, therefore, indicates widespread (∼ 95%) metastability at pressures higher than other metastable domains in Norway. Late-Caledonian amphibolite-facies retrogression was limited. The degree of reaction is related to the protolith composition and the interaction of fluid and deformation during the orogenic cycle, whereby metastability is associated with a lack of deformation and lack of fluids, either as a catalyst or as a component in hydration reactions. The three bodies appear to have been far less reactive than the external gneisses in this region, even though they followed a similar pressure–temperature evolution. The extent of metastable behaviour has implications for the protolith of the Western Gneiss Region, for the density evolution of high-pressure terranes and hence for the geodynamic evolution of mountain belts.

The high-pressure to ultrahigh-pressure eclogite transition in the Western Gneiss Region, Norway

2000 ◽  
Vol 12 (3) ◽  
pp. 667-687 ◽  
Author(s):  
Alice Wain ◽  
David Waters ◽  
Andrew Jephcoat ◽  
Helmut Olijynk
Keyword(s):  
High Pressure ◽  
Ultrahigh Pressure ◽  
Western Gneiss Region

scholarly journals Decompressional equilibration of the Midsund granulite from Otrøy, Western Gneiss Region, Norway

2019 ◽  
Vol 70 (6) ◽  
pp. 471-482
Author(s):  
Johanna Holmberg ◽  
Michał Bukała ◽  
Pauline Jeanneret ◽  
Iwona Klonowska ◽  
Jarosław Majka
Keyword(s):  
High Pressure ◽  
Thermodynamic Model ◽  
Thermodynamic Modelling ◽  
Ultrahigh Pressure ◽  
Stability Field ◽  
Uhp Metamorphism ◽  
Limited Evidence ◽  
Western Gneiss Region ◽  
Widespread Phenomenon ◽  
The Stability

Abstract The Western Gneiss Region (WGR) of the Scandinavian Caledonides is an archetypal terrain for high-pressure (HP) and ultrahigh-pressure (UHP) metamorphism. However, the vast majority of lithologies occurring there bear no, or only limited, evidence for HP or UHP metamorphism. The studied Midsund HP granulite occurs on the island of Otrøy, a locality known for the occurrence of the UHP eclogites and mantle-derived, garnet-bearing ultramafics. The Midsund granulite consists of plagioclase, garnet, clinopyroxene, relict phengitic mica, biotite, rutile, quartz, amphibole, ilmenite and titanite, among the most prominent phases. Applied thermodynamic modelling in the NCKFMMnASHT system resulted in a pressure–temperature (P–T) pseudosection that provides an intersection of compositional isopleths of XMg (Mg/Mg+Fe) in garnet, albite in plagioclase and XNa (Na/Na+Ca) in clinopyroxene in the stability field of melt + plagioclase + garnet + clinopyroxene + amphibole + ilmenite. The obtained thermodynamic model yields P–T conditions of 1.32–1.45 GPa and 875–970 °C. The relatively high P–T recorded by the Midsund granulite may be explained as an effect of equilibration due to exhumation from HP (presumably UHP) conditions followed by a period of stagnation under HT at lower-to-medium crustal level. The latter seems to be a more widespread phenomenon in the WGR than previously thought and may well explain commonly calculated pressure contrasts between neighboring lithologies in the WGR and other HP–UHP terranes worldwide.

TEM Study of Microstructure of Omphacite in High-Pressure and Ultrahigh-Pressure Eclogites

Mineralogy ◽  
2020 ◽  
pp. 39-48
Author(s):  
Meng Dawei ◽  
Wu Xiuling ◽  
Han Yujing ◽  
Liu Rong
Keyword(s):  
High Pressure ◽  
Ultrahigh Pressure
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