Tectonics of the Scandian orogeny and the Western Gneiss Region in southern Norway

Koenemann, Falk H.

doi:10.1007/bf00191497

Cited by 6 publications

(5 citation statements)

References 83 publications

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“…Smith 1995), any juxtaposition of UHP rocks against HP rocks must have occurred before the late-orogenic amphibolite-facies metamorphism. 0 I I [ I I I I I I I I T,b 0 200 400 600 800 Griffin & Brueckner (1980, 1985, Bjcrlykke (1983), Smith (1984, 1995), Gebauer et al (1985, Griffin et al (1985), Lux (1985), Steel et al (1985), Kullerud et aL (1986), Cotkin et al (1988), Dunning & Pedersen (1988), Chauvet & Dallmeyer (1992), Chauvet et al (1992), Koenemann (1993), Wilks & Cuthbert (1994), Krogh & Carswell (1995), Boundy et al (1996) and Wain (1997).…”

Section: Caledonian P -T -T Evolutionmentioning

confidence: 99%

Exhumation of UHP rocks by transtension in the Western Gneiss Region, Scandinavian Caledonides

Krabbendam¹,

Dewey²

1998

129

166

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In the Western Gneiss Region (WGR) in the Scandinavian Caledonides, Scandian eclogites (P = 16 to >28 kbar) occur in a large area of reworked Proterozoic gneisses, structurally below a series of Scandian nappes. The top-to-the-west, extensional Nordfjord-Sogn Detachment (NSD) separates the WGR from allochthonous units, which include several late-orogenic Devonian basins. The allochthon has not experienced Scandian high-pressure (HP) metamorphism. Below the NSD, the WGR is intensely deformed under late-orogenic amphibolite-facies conditions. This deformation is bulk-constrictional, as indicated by a linear feldspar fabric within augen gneisses and tight to isoclinal, lineationparallel folds within layered gneisses. In a later stage, the NSD, the WGR and the Devonian basins were folded by east-west trending folds, coeval with continuing movement along detachments.To explain these features we propose a transtensional model for the late-orogenic evolution of the WGR. Transtension in West Norway had a sinistral sense and was partially partitioned with increasing transtensional angle towards the NE-SW trending MOre-TrOndelag Fault Zone in the NW. During transtension, there is a strong tendency for rejuvenation of detachments, because detachments fold and may lock as they move. In the WGR, the younger Hornelen Detachment developed above the older NSD. Transtension was the principal exhumation mechanism of the HP and ultra-high-pressure (UHP) rocks in the WGR and involved oblique plate divergence of Laurentia and Baltica during the Early Devonian.The Western Gneiss Region (WGR) in West Norway is a large basement window within the Scandinavian Caledonides (Fig. 1). The WGR contains predominantly granodioritic and granitic gneisses, most of which are heterogeneously layered, some with augen textures.

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Section: Caledonian P -T -T Evolutionmentioning

confidence: 99%

Exhumation of UHP rocks by transtension in the Western Gneiss Region, Scandinavian Caledonides

Krabbendam¹,

Dewey²

1998

129

166

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“…The WGR in southwest Norway (Bryhni and Sturt 1985;Koenemann 1993;Andersen 1998) is a classic example of a (U)HP metamorphic terrane. The WGR is well known for its spectacular HP metamorphic rocks and associated garnet peridotites Medaris 1998, 2000;Carswell et al 1999;Cuthbert et al 1983Cuthbert et al , 2000Eskola 1921;Grif®n 1987;Krogh and Carswell 1995).…”

Section: Introductionmentioning

confidence: 99%

Non‐silicate inclusions in garnet from an ultra‐deep orogenic peridotite

et al. 2000

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Non-silicate solid inclusions in garnet from ultra-deep garnet peridotites, Otrùy, Western Gneiss Region, Norway, have been studied using light-optical, scanning and analytical electron microscopic techniques. Texturally, the investigated garnets reveal protogranular, porphyroclastic and equigranular microstructures. Protogranular and porphyroclastic garnets contain microstructural evidence of the former existence of`super-titanic' garnet. The microstructural evidence consists of exsolution textures involving rutile and ilmenite needles //`111b Grt as well as interstitial rutile grains. This exsolution microstructure is similar to the relict majoritic garnet microstructures found in the same peridotite. Some garnets contain both pyroxene and rutile exsolution.Other non-silicate mineral inclusions in protogranular and porphyroclastic garnet consist of nickel-iron alloys (Ni 99 Fe 01 ) and Cr-rich spinel. In addition, some protogranular, porphyroclastic and equigranular garnets contain composite Ni-Fe-Cu sulphide inclusions. The latter represent immiscible sulphide melt trapped within cracks that have healed.The original melting temperature of Ni-Fe-Cu sulphides was determined as being !1000 C and contrasts with temperatures derived from garnet±olivine±pyroxene mineral compositions using conventional geothermobarometry (c. 800 C/3 GPa). This contradiction is explained by the decoupling of microstructures and mineral chemistry; the microstructures were formed at higher temperatures than indicated by the current mineral chemistry. The decoupling of microstructures and current mineral chemistry has important applications for geodynamic models.

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“…S6ranne & Seguret 1987;Andersen & Jamtveit 1990;Andersen et al 1991;Fossen 1992Fossen , 1993bChauvet et al 1992;Andersen 1993;Dewey et al 1993;Koenemann 1993;Chauvet & S6ranne 1994;Wilks & Cuthbert 1994; see also Rey et aI. this volume), but few take into account the depth of knowledge which is available across the whole belt, particularly along the Sognefjord transect.…”

mentioning

confidence: 99%

Contraction, extension and timing in the South Norwegian Caledonides: the Sognefjord transect

Milnes

Wennberg

Skår

et al. 1997

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The Sognefjord transect through the lower to middle Palaeozoic Caledonian mountain belt in southern Norway provides one of the best and most completely documented examples of late collisional tectonics in an Alpine-type orogen. It exposes a 250km long cross-section from the cratonic foreland, in the east, through the heavily deformed continental margin (Baltica), to the remains of the Caledonian ocean (Iapetus) at the Norwegian west coast. Exceptionally detailed and complete structural data are available along the whole transect, together with good stratigraphic, radiometric, petrological, and geophysical control. In this synthesis, the structural data are analysed, in terms of the kinematics and relative age of the different deformation phases, and correlated along the whole transect. The analysis is then used, in conjunction with the other data, to carry out a retrodeformation, reconstructing the crustal geometry at different stages backward in time. The earliest of the present reconstructions (c. 410 Ma) marks the time of formation of the well-known West Norwegian eclogites, in an over-deepened root of Baltica which had developed in the ductile lower crust as a response to extreme crustal shortening. The brittle upper crust took up the shortening by the SE movement of a rigid sheet of Precambrian basement (Jotun complex) above the low-angle Jotunheimen contractional detachment, across a rigid wedge of the Baltic Shield. During the final stages of contraction (c. 410-395 Ma), the upper crust acted as an orogenic lid, against which the root 'collapsed' upwards by sub-vertical shortening and lateral E-W extension. During this process of inverted gravity spreading, the eclogites were carried upwards from 60-70 km to 40 km (exhumation phase 1, rate 2-3 mm a -1) and retrograded within their deforming gneissic matrix. At the end of this phase, the strain field in the upper crust changed from contraction to extension, concomitant with a broad up-doming (base Devonian unconformity) which caused a further 10 km exhumation by 385 Ma (exhumation phase 2, 1 mm a-l). This was followed by the main phase of crustal extension with the development of low-angle normal top-to-W or NW fault and shear zones, of which the Nordfjord-Sogn detachment was the most important (50 km of normal displacement). Exhumation in this phase took place by rapid uplift and erosion of the footwall of the detachment, causing the currently exposed eclogites in outer Sognefjord to rise the remaining 30 km (exhumation phase 3,1.5 mm a-l), to become juxtaposed against Devonian conglomerates on the hanging wall. The reconstructions confirm the general picture of eclogite exhumation in western Norway, and fill out some of the details. However, they do not support the idea that the process was due to extensional orogenic collapse caused by advective or convective lithospheric thinning. Although gravity played a significant role at various stages in the process, the main phase of crustal extension seems to have been mainly related to changes in Devonian plate...

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Tectonics of the Scandian orogeny and the Western Gneiss Region in southern Norway

Abstract: Two crust-forming events dominate the Pre-

Cited by 6 publications

References 83 publications

Exhumation of UHP rocks by transtension in the Western Gneiss Region, Scandinavian Caledonides

Exhumation of UHP rocks by transtension in the Western Gneiss Region, Scandinavian Caledonides

Non‐silicate inclusions in garnet from an ultra‐deep orogenic peridotite

Contraction, extension and timing in the South Norwegian Caledonides: the Sognefjord transect

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