A profile through the central scandinavian caledonides

Dyrekius, D; Gee, David G.; Gorbatschev, Roland; Ramberg, Hans; Zachrisson, Ebbe

doi:10.1016/0040-1951(80)90213-9

Cited by 26 publications

(5 citation statements)

References 40 publications

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“…The overall tectonostratigraphy of the Scandinavian Caledonides has been discussed at length elsewhere (Gee 1975b, Dyrelius et al 1980, Gee et al 1984) and will not be reviewed here. A variety of variably metamorphosed, largely metasedimentary sequences characterize lower, middle and lower portions of the upper allochthon.…”

Section: Regional Geological Settingmentioning

confidence: 98%

Polyphase tectonothermal evolution of the Scandinavian Caledonides

Dallmeyer¹

1988

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Summary A polyphase tectonothermal evolution characterizes many of the allochthonous sequences which constitute the Scandinavian Caledonides. Initial Late Cambrian consumption of Iapetus oceanic crust occurred outboard of the Baltoscandian margin with development of an island-arc above a west-dipping subduction complex. Imbrication, polydeformation and variably high-grade metamorphism of Baltoscandian miogeoclinal rocks and underlying Precambrian crystalline basement occurred within an accretionary prism which developed in the subduction complex. This resulted in eastward younging, diachronous metamorphism throughout the Early and Middle Ordovician. Cooling during subsequent uplift was regionally variable, and is reflected by the wide range of radiometric dates reported for the Baltoscandian allochthons (455–535 Ma). This early Caledonian activity has been termed the Finnmarkian orogeny; however, it is best viewed as a complex, diachronous series of tectonothermal events which variably affected the Baltoscandian margin from the Late Cambrian through the Middle Ordovician. Almost complete closure of the Iapetus Ocean appears to have been accomplished by the Late Ordovician when eugeoclinal terranes which had developed along the Laurentian margin were tectonically juxtaposed with eroded remnants of the Late Cambrian-Middle Ordovician arc. Initial imbrication of the Laurentian eugeoclinal sequences with the arc occurred during the Early Silurian (Late Llandovery). These were subsequently imbricated and infolded with predeformed Baltoscandian allochthons. The resultant composite allochthon was subsequently thrust eastward onto Silurian sedimentary successions deposited over previously metamorphosed Caledonian basement. This sequence of Early Silurian to Early Devonian tectonic events has been collectively termed the Scandian orogeny; however, they are regionally diachronous and should be bracketed with the local controls available. Scandian dates of 425–430 Ma are locally recorded in allochthons along eastern portions of the orogen and they probably date initial nappe translation to higher crustal levels along the Baltoscandian margin. In lower structural units Scandian dates range from 410 Ma in central to 385 Ma in western portions of the orogen. These are interpreted to date rapid cooling during the uplift associated with a crustal rebound which followed eastward translation of overriding allochthons.

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Section: Regional Geological Settingmentioning

confidence: 98%

Polyphase tectonothermal evolution of the Scandinavian Caledonides

Dallmeyer¹

1988

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“…see Corfu et al 2014). The Central Caledonian Transect (CCT), a profile crossing the mountain belt from the coast of Norway tö Ostersund in central Sweden, has played a key role during these investigations (Dyrelius et al 1980). Along this profile a major reflection seismic survey was conducted, which imaged the entire crust down to the Moho and provided images of the crustal structures related to the Caledonian deformation (Hurich et al 1989;Palm et al 1991;Juhojuntti et al 2001).…”

Section: Previous Geophysical Investigationsmentioning

confidence: 99%

Anisotropic Kirchhoff pre-stack depth migration at the COSC-1 borehole, central Sweden

Simon

Buske

Hedin

et al. 2019

Geophysical Journal International

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SUMMARYA remarkably well preserved representation of a deeply eroded Palaeozoic orogen is found in the Scandinavian Caledonides, formed by the collision of the two palaeocontinents Baltica and Laurentia. Today, after 400 Ma of erosion along with uplift and extension during the opening of the North Atlantic Ocean, the geological structures in central western Sweden comprise far transported allochthonous units, the underlying Precambrian crystalline basement, and a shallow west-dipping décollement that separates the two and is associated with a thin layer of Cambrian black shales. These structures, in particular the Seve Nappes (upper part of the Middle Allochthons), the Lower Allochthons and the highly reflective basement are the target of the two approximately 2.5 km deep fully cored scientific boreholes in central Sweden that are part of the project COSC (Collisional Orogeny in the Scandinavian Caledonides). Thus, a continuous 5 km tectonostratigraphic profile through the Caledonian nappes into Baltica’s basement will be recovered. The first borehole, COSC-1, was successfully drilled in 2014 and revealed a thick section of the seismically highly reflective Lower Seve Nappe. The Seve Nappe Complex, mainly consisting of felsic gneisses and mafic amphibolites, appears to be highly anisotropic. To allow for extrapolation of findings from core analysis and downhole logging to the structures around the borehole, several surface and borehole seismic experiments were conducted. Here, we use three long offset surface seismic profiles that are centred on the borehole COSC-1 to image the structures in the vicinity of the borehole and below it. We applied Kirchhoff pre-stack depth migration, taking into account the seismic anisotropy in the Seve Nappe Complex. We calculated Green’s functions using an anisotropic eikonal solver for a VTI (transversely isotropic with vertical axis of symmetry) velocity model, which was previously derived by the analysis of VSP (Vertical Seismic Profile) and surface seismic data. We show, that the anisotropic results are superior to the corresponding isotropic depth migration. The reflections appear significantly more continuous and better focused. The depth imaging of the long offset profiles provides a link between a high-resolution 3-D data set and the regional scale 2-D COSC Seismic Profile and complements these data sets, especially in the deeper parts below the borehole. However, many of the reflective structures can be observed in the different data sets. Most of the dominant reflections imaged originate below the bottom of the borehole and are situated within the Precambrian basement or at the transition zones between Middle and Lower Allochthons and the basement. The origin of the deeper reflections remains enigmatic, possibly representing dolerite intrusions or deformation zones of Caledonian or pre-Caledonian age.

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“…In central Jämtland, Gee (1975) and Dyrelius et al (1980) proposed that the Müllfjället and Tømmerås Window-Basement (Fig. 1) were parautochthonous (or allochthonous, but not far-travelled, if an upper imbricate of the Window-Basement).…”

Section: Published Restorations Of the Window-basementmentioning

confidence: 99%

Restoration of the external Scandinavian Caledonides

Rice

Anderson

2016

Geol. Mag.

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-Three models are evaluated for restoring basement rocks coring tectonic windows (WindowBasement) in the Scandinavian Caledonides; parautochthonous (Model I) and allochthonous (models II/III), with initial imbrication of the Window-Basement post-dating or pre-dating, respectively, that in the external imbricate zone (Lower Allochthon). In Model I, the Window-Basement comes from the eastern margin of the basin now imbricated into the Lower Allochthon, while in models II/III it comes from the western margin. In Model II, the Window-Basement formed a basement-high between Tonian and Cryogenian sediments imbricated into the Middle and Lower allochthons; in Model III deposition of the Lower Allochthon sediments commenced in Ediacaran times. Balanced cross-sections and branch-line restorations of four transects (Finnmark-Troms, Västerbotten-Nordland, Jämtland-Trøndelag, Telemark-Møre og Romsdal) show similar restored lengths for the models in two transects and longer restorations for models II/III in the other transects. Model I can result in c. 280 km wide gaps in the restored Lower Allochthon, evidence for which is not seen in the sedimentology. The presence of <3 km thick alluvial-fan deposits at the base of the Middle Allochthon indicates proximal, rapidly uplifting basement during Tonian-Cryogenian periods, taken as the origin of the Window-Basement during thrusting in models II/III. Model I requires multiple changes in thrusting-direction and predicts major thrusts or back-thrusts, currently unrecognized, separating parts of the Lower Allochthon; neither are required in models II/III. Metamorphic data are consistent with models II/III. Despite considerable along-strike structural variability in the external Scandinavian Caledonides, models II/III are preferred for the restoration of the Window-Basement.

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A profile through the central scandinavian caledonides

Cited by 26 publications

References 40 publications

Polyphase tectonothermal evolution of the Scandinavian Caledonides

Polyphase tectonothermal evolution of the Scandinavian Caledonides

Anisotropic Kirchhoff pre-stack depth migration at the COSC-1 borehole, central Sweden

Restoration of the external Scandinavian Caledonides

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