Postcollisional extension of the Caledonide orogen in Scandinavia: Structural expressions and tectonic significance

Fossen, Haakon; Rykkelid, Erling

doi:10.1130/0091-7613(1992)020<0737:peotco>2.3.co;2

Cited by 77 publications

(46 citation statements)

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“…425 Ma. Until recently, extensional structures in the East Greenland Caledonides were interpreted to reflect post-Caledonian, Devonian-aged extension (e.g., McClay et al 1986;Larsen and Bengård 1991;Hartz and Andresen 1995) mirroring evidence for widespread, post-orogenic extension in Scandinavia (e.g., Fossen and Rykkelid 1992;Fossen and Holst 1995). Our results suggest that extension took place at middle and upper crustal levels and occurred synchronously with or very soon after the main phase of contraction.…”

Section: Implications For the Role Of Extension In The Development Ofmentioning

confidence: 68%

Geologic constraints on middle-crustal behavior during broadly synorogenic extension in the central East Greenland Caledonides

White

Hodges

Martin

et al. 2002

International Journal of Earth Sciences

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Structural and U-Pb geochronologic data from the Forsblad Fjord area of East Greenland (72°30′N) indicate close spatial and temporal ties between orogen-parallel shear and extensional deformation during Caledonian orogenesis. This territory is composed of three tectonostratigraphic units separated by two splays of the Fjord Region Detachment System (FRDS), a principal extensional fault system of the East Greenland Caledonides that was active in Silurian time. The oldest Caledonian fabrics in Forsblad Fjord, which developed at upper amphibolite facies metamorphic conditions, indicate that there was north-south, lateral extrusion of ductile middle-crustal material synchronous with approximately east-west shortening. U-Pb dating of synkinematic granitic leucosomes in migmatitic schists and gneisses demonstrates that this process was underway at ca. 425 Ma. Subsequently, east-west extension along the two splays of the FRDS truncated the older fabrics; the structurally highest of these shear zones -the Tindern detachment -was active as early as ca. 424 Ma. This implies either that there was a rapid transition from Caledonian shortening and possible transpressional deformation to post-orogenic collapse, or our preferred interpretation that extension was synorogenic. The FRDS shares many structural characteristics with the South Tibetan Detachment System of the Cenozoic Himalayan orogen but exhibits two important differences. First, while the South Tibetan system developed in the down-going Indian plate during the India-Eurasia collision, the Fjord Region system developed in the overriding Laurentian plate during the collision of Laurentia with Baltica. Second, whereas the exposed extensional structures in the Himalayas developed in the upper crust and are only inferred to have extended to deeper levels, those in the Forsblad Fjord area were demonstrably active at middle-crustal levels. Evidence for broadly coeval extension and contraction at differen t structural levels in both mountain belts emphasizes the general importance of crustal decoupling in the collisional orogenic process, and implies that synorogenic extensional deformation is not strictly an upper crustal phenomenon.

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Section: Implications For the Role Of Extension In The Development Ofmentioning

confidence: 68%

Geologic constraints on middle-crustal behavior during broadly synorogenic extension in the central East Greenland Caledonides

White

Hodges

Martin

et al. 2002

International Journal of Earth Sciences

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“…There are however asymmetric folds and other kinematic structures indicating top-to-the-west transport in deformed Caledonian rocks, particularly in the Ofoten area (Steltenpohl & Bartley 1988). Fossen & Rykkelid (1992) and Rykkelid & Andresen (1994) suggested the presence of west-dipping extensional shear zone of the Mode II type described from southern Norway, but with a lesser amount of extension than that of the major shear zones in southern Norway.…”

Section: Extensional Structures In Central and Northern Norwaymentioning

confidence: 90%

Extensional tectonics in the North Atlantic Caledonides: a regional view

Fossen

2010

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151

115

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Extensional structures characterize significant parts of the North Atlantic Caledonides. Silurian extensional deformation took place, particularly in the heated crust in the southern Greenland Caledonides, but the majority of the mapped extensional structures are Devonian (403-380 Ma). They formed by reactivation of low-angle Caledonian thrusts and by the formation of hinterland-dipping shear zones, of which the largest system is located in SW Norway and related to exhumation of the subducted margin of Baltica. The Devonian extension was concentrated to the central and southern part of the Caledonides, with maximum extension occurring in the area between the Western Gneiss Region of SW Norway and the Fjord Region of East Greenland. Kinematic data indicate that the main tectonic transport direction was toward the hinterland, and this pattern suggests that the main Devonian extension/transtension in the southern part of the North Atlantic region was postcontractional while strike-slip motions and possibly transpression occurred farther north. Late Devonian to enigmatic Early Carboniferous ages from UHP metamorphic assemblages in NE Greenland suggest that intracontinental subduction was going on in NE Greenland at a time when extensional deformation governed the rest of the orogenic belt.

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“…However, these structures were reactivated and/or overprinted by late Caledonian extension and by subsequent brittle deformation throughout Mesozoic and Cainozoic times (e.g. Fossen and Rykkelid, 1992;Eide, 2002;Osmundsen et al 2003). Recent tectonic activity, as it is expressed by post-glacial faults and recent earthquakes, may either be related to the effects of post-glacial rebound following the removal of the load of the late Pleistocene inland ice, or to plate tectonic effects, probably the ridge push of the North-Atlantic mid-ocean ridge (e.g.…”

Section: Neotectonics In a Part Of West-central Scandinaviamentioning

confidence: 99%

Natural electromagnetic radiation (EMR) and its application in structural geology and neotectonics

Greiling

Obermeyer²

2010

J Geol Soc India

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Natural electromagnetic radiation (EMR) impulses are emitted from rocks under stress. Electromagnetic emission may start during crystal deformation prior to and during the nucleation phase of nanocracks. The emission direction is either parallel with or normal to the crack surfaces. The EMR magnetic component is measured by the sensor or aerial of an instrument, the Cerescope, at frequencies from 5 to 50 kHz. Measurements at the surface show directions of recent stresses remarkably well. A calibration of EMR intensity in terms of stress magnitude is possible in tunnels, where the overburden pressure can be calculated. Two examples from the Upper Rhine Graben and NW India show EMR line measurements. In both cases, stress concentrations at fault or bedding surfaces can be detected. These surfaces can be regarded as tectonically active. Two further examples of EMR determinations in tunnels give more detailed information on the regional stress field. The example from the Swiss Jura fold-and-thrust belt shows directional results, with different directions beneath and above the regional detachment horizon at the base of the belt. The example from central Scandinavia shows a late Caledonian shear zone as a boundary between two recent stress domains, and gives absolute values of stress.

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Postcollisional extension of the Caledonide orogen in Scandinavia: Structural expressions and tectonic significance

Cited by 77 publications

References 0 publications

Geologic constraints on middle-crustal behavior during broadly synorogenic extension in the central East Greenland Caledonides

Geologic constraints on middle-crustal behavior during broadly synorogenic extension in the central East Greenland Caledonides

Extensional tectonics in the North Atlantic Caledonides: a regional view

Natural electromagnetic radiation (EMR) and its application in structural geology and neotectonics

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