Shear zone structures in the Øygarden area, West Norway

Fossen, Haakon; Rykkelid, Erling

doi:10.1016/0040-1951(90)90333-4

Cited by 58 publications

(17 citation statements)

References 29 publications

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“…oblique to the streamlines in the material, Cobbold and Quinquis, 1980) may fold during progressive deformation in extensional detachments in the same manner as described for thrust or transcurrent ductile shear zones (see review by Williams et al, 1994). Outcrop to kilometre-scale folds have been described in extensional detachment shear zones in the Apennines (Carmignani et al, 1994) and Caledonides (Fossen and Rykkelid, 1990). Large recumbent fold structures in Fig.…”

Section: Progressive Folding In Extensional Ductile Shear Zonesmentioning

confidence: 89%

“…Although there are some cases where folds may form parallel to the displacement direction (Bell and Hammond, 1984;Fossen and Rykkelid, 1990; also see Section 5.3 below), folds in ductile shear zones generally initiate with hinges normal, or at a high angle to the displacement direction. At low shear strain, folds are overturned towards the sense of shear and are often noncylindrical (c.f.…”

Section: Progressive Folding In Extensional Ductile Shear Zonesmentioning

confidence: 99%

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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: Progressive Folding In Extensional Ductile Shear Zonesmentioning

confidence: 89%

Section: Progressive Folding In Extensional Ductile Shear Zonesmentioning

confidence: 99%

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

Harris

Koyi

Fossen

2002

Earth-Science Reviews

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“…The Oygarden Complex, where sample N1 was collected, was pervasively deformed and metamorphosed under amphibolite facies conditions during hinterland-directed (topto-the-W) shearing [Fossen and Rykkelid, 1990]. Decreasing temperatures during postcontractional extensional deformation are expressed by a change from ductile deformation to faulting where striated, epidote-coated fault surfaces indicate NW-SE extension [Fossen, 1998].…”

Section: Geologic Settingmentioning

confidence: 99%

Early Paleozoic orogenic collapse, tectonic stability, and late Paleozoic continental rifting revealed through thermochronology of K‐feldspars, southern Norway

Dunlap¹,

Fossen²

1998

Tectonics

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“…A strong crystallographic preferred orientation (CPO) of omphacite within shear zone eclogites indicates deformation occurred by slip along [Ool] while the eclogites were deformed under high-P, deep crustal conditions. Modified from Kolderup & Kolderup (1940) and Fossen & Rykkeild (1990).…”

Section: Introductionmentioning

confidence: 99%

Structural development and petrofabrics of eclogite facies shear zones, Bergen Arcs, western Norway: implications for deep crustal deformational processes

Boundy

Fountain

Austrheim

1992

Journal Metamorphic Geology

167

125

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A B S T R A C T Caledonian eclogite facies shear zones developed from Grenvillian garnet granulite facies anorthosites and gabbros in the Bergen Arcs of western Norway allow direct investigation of the relations between macroscopic structures and crystallographic preferred orientation (CPO) in lower continental crust. Field relations on the island of Holsn~y show that the eclogites formed locally from granulite facies rocks by progressive development of: (1) eclogite adjacent to fractures; (2) eclogite in discrete shear zones (<2 m thick); (3) eclogite breccia consisting of <80% well-foliated eclogite that wraps around rotated granulite blocks; and (4) anastomosing, subparallel, eclogite facies shear zones 30-100 m thick continuous over distances > 1 km within the granulite terrane. These shear zones deformed under eclogite facies conditions at an estimated temperature of 670 f 50°C and a minimum pressure of 1460 MPa, which corresponds to depths of >55 km in the continental crust. Detailed investigation of the major shear zones shows the development of a strong foliation defined by the shape preferred orientation of omphacite and by alternating segregations of omphacite/garnet-rich and kyanite/zoisite-rich layers. A consistent lineation throughout the shear zones is defined by elongate aggregates of garnet and omphacite. The CPO of omphacite, determined from five-axis universal stage measurements, shows a strong b-axis maximum normal to foliation, and a c-axis girdle within the foliation plane with weak maxima parallel to the lineation direction. These patterns are consistent with deformation of omphacite by slip parallel to [Ool] and suggest glide along (010). The lineation and CPO data reveal a consistent sense of shear zone movement, although the displacement was small. Localized faulting of high-grade rocks accompanied by fluid infiltration can be an important mode of failure in the lower continental crust. Field relations show that granulite facies rocks can exist in a metastable state under eclogite facies conditions and imply that the lower crust can host differing metamorphic facies at the same depth. Deformation of granulite and partial conversion to eclogite, such as is exposed on Holsn~y Island, may be an orogenic-scale process in the lowermost crust of collisional orogens.

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Shear zone structures in the Øygarden area, West Norway

Cited by 58 publications

References 29 publications

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

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

Early Paleozoic orogenic collapse, tectonic stability, and late Paleozoic continental rifting revealed through thermochronology of K‐feldspars, southern Norway

Structural development and petrofabrics of eclogite facies shear zones, Bergen Arcs, western Norway: implications for deep crustal deformational processes

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