Fluid controlled eclogitization of granulites in deep crustal shear zones, Bergen arcs, Western Norway

Jamtveit, Bjørn; Bucher-Nurminen, Kurt; Austrheim, Håkon

doi:10.1007/bf00306442

Cited by 198 publications

(164 citation statements)

References 25 publications

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“…Using this approach, Holland (1979) showed that kyanite-paragonite eclogites from the Tauern window, Austrian Alps, equilibrated with a water-dominated fluid phase. The mineralogy of the present quartz-paragonite/ phengite veins is similar to the Tauern window eclogites, and a thermodynamic analysis accordingly suggests a water-dominated fluid composition (Jamtveit et al, 1989).…”

Section: Geological Settingsupporting

confidence: 57%

Fluid inclusions in granulites and eclogites from the Bergen Arcs, Caledonides of W. Norway

1990

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The Grenvillian granulite-facies complex on Holsn0y island, Bergen Arcs, W. Norway, has been metamorphosed at eclogite-facies conditions during the Caledonian orogeny (ca. 425 Ma). The granulite-eclogite facies transition takes place along shear zones and fluid pathways. Mineral thermobarometry indicates PT conditions of 800-900~ and 8-10kbar for the Proterozoic granulite facies metamorphism and 700-800 ~ and 16-19 kbar for the eclogite-forming event. Quartz in the granulite facies complex contains CO 2 fluid inclusions with less than 2.5 mole percent N2; the molar volumes are compatible with the PT conditions of the Proterozoic granulite metamorphism. Quartz in pegmatitic quartz + omphacite and quartz + phengite/paragonite veins coeval with shear-zone eclogites contain N2 + CO2 fluid inclusions. Combined laser Raman microanalysis and microthermometry show that the least disturbed inclusions have )(co 2 ---0.1-0.3, and molar volumes less than 40 cm3/mole, which may agree with the PT conditions during Caledonian high-pressure metamorphism. Younger, lowdensity N 2 and N2-H20 fluid inclusions are the results of decrepitation and redistribution of early inclusions during the retrograde PT evolution of the eclogites.

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Section: Geological Settingsupporting

confidence: 57%

Fluid inclusions in granulites and eclogites from the Bergen Arcs, Caledonides of W. Norway

1990

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“…Ohuchi et al (2011) also reported that the B-type LPO of olivine was formed at even higher pressures, about 7 GPa at T = 1,220°C and 1,400°C. However, for the anorthosite bodies in the Lindås Nappe complex surrounding the samples, the Grenvillian orogeny occurred at a pressure of 1 GPa and the Caledonian orogeny occurred at 1.5 to 2.1 GPa (Austrheim and Griffin 1985;Glodny et al 2008;Jamtveit et al 1990). In both cases, the pressure was less than 3 GPa, and hence, pressure alone could not have changed the easiest slip direction of olivine in the study area.…”

Section: Lpo Of Olivinementioning

confidence: 97%

“…Typically, this foliation is characterized by disc-shaped coronas that are oriented in the same direction and by alternating plagioclase-rich and mafic layers that produce a strong banding. The granulitefacies anorthositic rocks were transformed, locally, to dense eclogite-facies rocks during the Caledonian orogeny (650°C to 700°C, 1.5 to 2.1 GPa) (Jamtveit et al 1990;Glodny et al 2008).…”

Section: Geological Setting and Sample Descriptionmentioning

confidence: 99%

“…The phase transition between spinel lherzolite and garnet lherzolite occurs between 1.6 GPa at 800°C and 1.9 GPa at 1,100°C (O'Neill 1981). Pressure was determined to be lower than 1.0 GPa during the Grenvillian orogeny (Austrheim and Griffin 1985) and to range 1.5 to 2.1 GPa during the Caledonian orogeny (Glodny et al 2008;Jamtveit et al 1990). …”

Section: Two-stage Deformations and Their Implications For Seismic Anmentioning

confidence: 99%

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Characterization of olivine fabrics and mylonite in the presence of fluid and implications for seismic anisotropy and shear localization

Jung

Austrheim

2014

Earth Planet Sp

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The Lindås Nappe, Bergen Arc, is located in western Norway and displays two high-grade metamorphic structures. A Precambrian granulite facies foliation is transected by Caledonian fluid-induced eclogite-facies shear zones and pseudotachylytes. To understand how a superimposed tectonic event may influence olivine fabric and change seismic anisotropy, two lenses of spinel lherzolite were studied by scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD) techniques. The granulite foliation of the surrounding anorthosite complex is displayed in ultramafic lenses as a modal variation in olivine, pyroxenes, and spinel, and the Caledonian eclogite-facies structure in the surrounding anorthosite gabbro is represented by thin (<1 cm) garnet-bearing ultramylonite zones. The olivine fabrics in the spinel bearing assemblage were E-type and B-type and a combination of A-and B-type lattice preferred orientations (LPOs). There was a change in olivine fabric from a combination of A-and B-type LPOs in the spinel bearing assemblage to B-and E-type LPOs in the garnet lherzolite mylonite zones. Fourier transform infrared (FTIR) spectroscopy analyses reveal that the water content of olivine in mylonite is much higher (approximately 600 ppm H/Si) than that in spinel lherzolite (approximately 350 ppm H/Si), indicating that water caused the difference in olivine fabric. Fabric strength of olivine gets weaker as the grain size reduced, and as a result, calculated seismic properties for the two deformation stages reveal that P-and S-velocity anisotropies are significantly weaker in the mylonite. Microtextures and LPO data indicate that the deformation mechanism changed from dominant dislocation creep in spinel lherzolite to dislocation creep accompanied by grain-boundary sliding in mylonite. Shear localization in the mylonite appears to be originated from the grain size reduction through (1) enhanced dynamic recrystallization of olivine in the presence of water and (2) Zener pinning of clinopyroxene or (3) by ultracomminution during the pseudotachylyte stage.

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“…An alternative view is that the association of fluids and metamorphic activity reflects the catalytic, rather than causal, role of fluids in metamorphism. This latter view is supported by numerical modeling of crustal metamorphism which suggests that regional scale metamorphic fluid fluxes, estimated to be on the order of 10 −8 −10 −10 kg/m 2 −s, are too small to significantly alter the thermal development of metamorphic systems (e.g., Peacock 1987Peacock , 1989Brady 1989;Connolly & Thompson 1989;Jamtveit et al 1990). Thus, it appears that anomalously large fluxes are required to generate notable thermal effects.…”

Section: Introductionmentioning

confidence: 93%

Mid-Crustal Focused Fluid Movement: Thermal Consequences and Silica Transport

Connolly¹

1997

Fluid Flow and Transport in Rocks

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Numerical models have been constructed to assess the thermal consequences and silica transport that would result if water released by regional metamorphic dehydration or cooling plutons were focused into large-scale (10 km) fracture zones. Two fracture zone model geometries have been considered, in one the fracture zone is planar, and in the other the fracture zone is radially symmetric. In both models dispersion and collection of fluids is simulated. None of the channelized flow models appear to provide an effective mechanism for producing pervasive quartz veining, but the very high fluid fluxes generated by plutons are capable of producing extensive silicification (>4 vol %) within the vertical portion of a fracture zone, similar to that found in stock-work ore deposits.In the case of fluids produced by high temperature dehydration, more silica is precipitated at depth during focusing (> 1 vol %) and within the fracture zones than is precipitated during dispersion (< 0.2 vol %). This reflects both the relatively high rate of change in silica solubility with decompression at depth, and the low solubility at the shallower conditions.

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Fluid controlled eclogitization of granulites in deep crustal shear zones, Bergen arcs, Western Norway

Cited by 198 publications

References 25 publications

Fluid inclusions in granulites and eclogites from the Bergen Arcs, Caledonides of W. Norway

Fluid inclusions in granulites and eclogites from the Bergen Arcs, Caledonides of W. Norway

Characterization of olivine fabrics and mylonite in the presence of fluid and implications for seismic anisotropy and shear localization

Mid-Crustal Focused Fluid Movement: Thermal Consequences and Silica Transport

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