Processing of crust in the root of the Caledonian continental collision zone: the role of eclogitization

Austrheim, Håkon; Erambert, Muriel; Engvik, Ane K.

doi:10.1016/s0040-1951(96)00291-0

Cited by 140 publications

(127 citation statements)

References 66 publications

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“…These observations of fabric change induced by water, in the Hundskjeften peridotite, are consistent with previous experimental studies on the deformation of olivine at high pressures and temperatures in the presence of water (Jung and Karato 2001a;Katayama et al 2004;Jung et al 2006). Previous studies on surrounding granulite bodies in Bergen Arc report that fluids, which infiltrated through the pseudotachylyte, promoted eclogitization during the Caledonian orogeny (Austrheim 1987 1990; Austrheim and Boundy 1994;Austrheim et al 1997). It is also important to consider the possibility that the development of mylonite foliation was associated with reactions that convert spinel lherzolite to garnet lherzolite.…”

Section: Lpo Of Olivinesupporting

confidence: 90%

“…Lindås Nappe is the largest of these units. It is believed that the eclogite facies overprinting occurred when Lindås Nappe formed part of the root zone to the Caledonian mountain belt (Austrheim 1987;Austrheim et al 1997;Boundy et al 1997). The main component of Lindås Nappe is anorthosite and includes other members of the anorthosite-mangeritegranite-charnockite (AMGC) suite of rocks (Austrheim 1990).…”

Section: Geological Setting and Sample Descriptionmentioning

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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Section: Lpo Of Olivinesupporting

confidence: 90%

Section: Geological Setting and Sample Descriptionmentioning

confidence: 99%

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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“…Granulites from the middle of the crust, produced by melt removal, will be dry, having lost both water and CO 2 . As Austrheim et al (1997) have shown, such rocks react very slowly to changes in pressure and temperature. As a result their P, T history may only be recorded (if it is recorded at all) by the growth of small mineral grains along fractures.…”

Section: Discussionmentioning

confidence: 99%

Speculations on the formation of cratons and cratonic basins

McKenzie

2016

Earth and Planetary Science Letters

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“…In this case, the V p /V s ratio observed beneath seismic networks are higher than expected for the presence of eclogite (V p /V s 1.77-1.78, Thompson et al 2010 and reference therein). The absence of a high velocity layer at the base of the crust could be the result of delamination of an eclogitized lower crust beneath the orogen (Austrheim et al 1997).…”

Section: N T E R P R E Tat I O N a N D Discussionmentioning

confidence: 99%

Crustal properties of the northern Scandinavian mountains and Fennoscandian shield from analysis of teleseismic receiver functions

Mansour

England

Fishwick

et al. 2018

Geophysical Journal International

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S U M M A R YThe presence of high mountains along passive margins is not unusual, as shown by their presence in several regions (Scandinavia, Greenland, East US, SW Africa, Brazil, West India and SE Australia). However, the origin of this topography is not well understood. The mountain range between the Scandinavian passive margin and the Fennoscandian shield is a good example. A simple Airy isostatic model would predict a compensating root beneath the mountains but existing seismic measurements of variations in crustal thickness do not provide evidence of a root of sufficient size to produce the necessary compensation. In order to better constrain the physical properties of the crust in northern Scandinavia, two broad-band seismic networks were deployed between 2007 and 2009 and between 2013 and 2014. A new map of crustal thickness has been produced from P-receiver function analysis of teleseismic data recorded at 31 seismic stations. The map shows an increase in crustal thickness from the Atlantic coast (38.7 ± 1.8 km) to the Gulf of Bothnia (43.5 ± 2.4 km). This gradient in thickness demonstrates that the Moho topography does not mirror the variation in surface topography in this region. Thus, classical Airy isostatic models cannot explain how the surface topography is supported. New maps showing variation in Poisson's ratio and Moho sharpness together with forward and inverse modelling provide new information about the contrasting properties of the Fennoscandian shield and crust reworked by the Caledonian orogeny. A sharp Moho transition (R > 1) and low value of V s (3.5 ± 0.2 km s −1 ) are observed beneath the orogen. The shield is characterized by a gradual transition across the Moho (R < 1) and V s of 3.8 ± 0.1 km s −1 which is more typical of average continental crust. These observations are explained by a Fennoscandian shield underplated with a thick layer of high velocity, high density material. It is proposed that this layer has been removed or reworked beneath the orogen.

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Processing of crust in the root of the Caledonian continental collision zone: the role of eclogitization

Cited by 140 publications

References 66 publications

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

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

Speculations on the formation of cratons and cratonic basins

Crustal properties of the northern Scandinavian mountains and Fennoscandian shield from analysis of teleseismic receiver functions

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