Late Caledonian extension in the Ofoten area, northern Norway

Rykkelid, Erling; Andresen, Arild

doi:10.1016/0040-1951(94)90127-9

Cited by 33 publications

(20 citation statements)

References 21 publications

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“…A similar, reactivated thrust origin has been established for other extensional detachments in the Scandinavian Caledonides Rykkelid and Andresen, 1994;Wennberg, 1996;Andersen, 1998). Normal slip on the pre-existing foliation and formation of reverse shear bands and NW-verging folds has been noted from the Kvamshesten Detachment, West Norway (Fig.…”

Section: Centrifuge Modelling Of Structures In High-grade Rocks Durinsupporting

confidence: 72%

Mechanisms for folding of high-grade rocks in extensional tectonic settings

Harris

Koyi

Fossen

2002

Earth-Science Reviews

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This review of structures developed in extensional high-grade terrains, combined with results of centrifuge analogue modelling, illustrates the range of fold styles and mechanisms for folding of amphibolite to granulite facies rocks during rifting or the collapse of a thrust-thickened orogen. Several extensional fold mechanisms (such as folding within detachment shear zones) are similar to those in contractional settings. The metamorphic P -T -t path, and not fold style or mode of formation, is therefore required to determine the tectonic setting in which some folds developed. Other mechanisms such as rollover above and folding between listric normal shear zones, and folding due to isostatic adjustments during crustal thinning, are unique to extensional tectonic settings. Several mechanisms for folding during crustal extension produce structures that could easily be misinterpreted as implying regional contraction and hence lead to errors in their tectonic interpretation. It is shown that isoclinal recumbent folds refolded by open, upright folds may develop during regional extension in the deep crust. Folds with a thrust sense of asymmetry can develop due to high shear strains within an extensional detachment, or from enhanced back-rotation of layers between normal shear zones. During back-rotation folding, layers rotated into the shortening field undergo further buckle folding, and all may rotate towards orthogonality to the maximum shortening direction. This mechanism explains the presence of many transposed folds, folds with axial planar pegmatites and folds with opposite vergence in extensional terrains. Examples of folds in high-grade rocks interpreted as forming during regional extension included in this paper are from the Grenville Province of Canada, Norwegian

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Section: Centrifuge Modelling Of Structures In High-grade Rocks Durinsupporting

confidence: 72%

Mechanisms for folding of high-grade rocks in extensional tectonic settings

Harris

Koyi

Fossen

2002

Earth-Science Reviews

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“…In the Devonian, the nappes were dismembered by a late gravity collapse phase of the Scandian orogeny (Rykkelid & Andresen, 1994;Braathen et al, 2002;Eide et al, 2002).…”

Section: Tectonic Structuresmentioning

confidence: 99%

Relation between seismicity and tectonic structures offshore and onshore Nordland, northern Norway

Janutyte¹,

Lindholm²,

Olesen³

2017

NJG

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“…Structures formed at various upper to lower crustal levels related to the extensional collapse have been identified in several on-shore cross-sectional traverses along-strike of the orogen (e.g., Norton, 1986;Séranne and Séguret, 1987;Andersen and Jamtveit, 1990;Fossen, 1992;Rykkelid and Andresen, 1994). The late-to post-orogenic extension in southern Norway resulted in penetrative reworking and decompression of Caledonian high-pressure metamorphic rocks, formation of large extensional detachments and the Devonian supra-detachment basins Osmundsen, 1996;Osmundsen et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Extensional tectonics in the Caledonides of southern Norway, an overview

1998

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The extensional collapse of the Scandinavian Caledonides resulted in rapid tectonic denudation of the orogen, exhumation of high-and ultra-high-pressure metamorphic rocks and provided a structural template for the formation of Devonian supra-detachment sedimentary basins. The geometry and intensity of the extensional deformation show considerable variation vertically in the crustal section as well as horizontally from east to west across the orogen. The most prominent structural feature related to the extension in central-south Norway is the change in the direction of tectonic transport, from the easterly directed nappe translation during the Silurian Scandian Orogeny, to top-westerly directed sense of shear during the extension. The Fennoscandian basement was little affected by extension in the eastern Caledonides. In the west, however, top-to-the-west shear zones are commonly observed in basement windows. Deformation affecting the Cambrian to Late Silurian rocks in the Caledonian foreland developed a typical of foreland fold and thrust belt geometry. Deformation in the foreland was apparently contemporaneous with the extension-related decompression of the high-pressure rocks in the hinterland. Thrusting in the foreland may thus have been driven by gravitational collapse, and as such have important similarities to the foreland-hinterland relationships of the Himalayan-Tibetan region. The basal contacts of the Jotun and other major nappes constitute prominent shear zones in which fabrics related to thrusting have been mostly destroyed by extensional shearing. The high structural levels of the Western Gneiss Region, adjacent to the western margin of the Jotun Nappe, were only moderately affected by the extensional deformation. Consequently, the Proterozoic orthogneiss complexes are generally well preserved in this area. The westernmost and structurally lowermost parts of the Western Gneiss Region have, however, been subjected to extreme overburden during the Caledonian continental collision. Initial, near-isothermal decompression of the high-pressure rocks occurred by non-rotational vertical shortening-horizontal stretching at eclogite-to amphibolite-facies conditions; at a later stage, decompression and cooling from amphibolite to greenschist facies occurred by rotational deformation associated with the large-scale extensional detachments. The initial extensional deformation in the hanging wall of the detachments in western Norway commenced at greenschist-facies conditions, and became progressively more brittle and localised as the complexes were exhumed in the Late Silurian to Middle Devonian. Major syn-depositional normal faults in the hanging wall of the extensional detachments eventually controlled sedimentation in the Devonian supra-detachment basins.

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Late Caledonian extension in the Ofoten area, northern Norway

Cited by 33 publications

References 21 publications

Mechanisms for folding of high-grade rocks in extensional tectonic settings

Mechanisms for folding of high-grade rocks in extensional tectonic settings

Relation between seismicity and tectonic structures offshore and onshore Nordland, northern Norway

Extensional tectonics in the Caledonides of southern Norway, an overview

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