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COSC-1 - drilling of a subduction-related allochthon in the Palaeozoic Caledonide orogen of Scandinavia

Lorenz, H.; Rosberg, J. -E.; Juhlin, C.; Bjelm, Leif LU ; Almqvist, B. S. G.; Berthet, T.; Conze, R.; Gee, D. G.; Klonowska, I. and Pascal, C., et al. (2015) In Scientific Drilling 19. p.1-11
Abstract
The Collisional Orogeny in the Scandinavian Caledonides (COSC) scientific drilling project focuses on mountain building processes in a major mid-Palaeozoic orogen in western Scandinavia and its comparison with modern analogues. The project investigates the subduction-generated Seve Nape Complex. These in part under ultra-high-pressure conditions metamorphosed outer continental margin and continent-ocean transition zone assemblages were emplaced onto the Baltoscandian platform and there influenced the underlying allochthons and the basement. COSC-1 is the first of two ca. 2.5 km deep, fully cored drill holes located in the vicinity of the abandoned Froa mine, close to the town of Are in Jamtland, central Sweden. It sampled a thick section... (More)
The Collisional Orogeny in the Scandinavian Caledonides (COSC) scientific drilling project focuses on mountain building processes in a major mid-Palaeozoic orogen in western Scandinavia and its comparison with modern analogues. The project investigates the subduction-generated Seve Nape Complex. These in part under ultra-high-pressure conditions metamorphosed outer continental margin and continent-ocean transition zone assemblages were emplaced onto the Baltoscandian platform and there influenced the underlying allochthons and the basement. COSC-1 is the first of two ca. 2.5 km deep, fully cored drill holes located in the vicinity of the abandoned Froa mine, close to the town of Are in Jamtland, central Sweden. It sampled a thick section of the lower part of the Seve Complex and was planned to penetrate its basal thrust zone into the underlying lower-grade metamorphosed allochthon. The drill hole reached a depth of 2495.8m and nearly 100% core recovery was achieved. Although planning was based on existing geological mapping and new high-resolution seismic surveys, the drilling resulted in some surprises: the Lower Seve Nappe proved to be composed of rather homogenous gneisses, with only subordinate mafic bodies, and its basal thrust zone was unexpectedly thick (>800 m). The drill hole did not penetrate the bottom of the thrust zone. However, lower-grade metasedimentary rocks were encountered in the lowermost part of the drill hole together with garnetiferous mylonites tens of metres thick. The tectonostratigraphic position is still unclear, and geological and geophysical interpretations are under revision. The compact gneisses host only eight fluid conducting zones of limited transmissivity between 300m and total depth. Downhole measurements suggest an uncorrected average geothermal gradient of similar to 20 degrees C km(-1). This paper summarizes the operations and preliminary results from COSC-1 (ICDP 5054-1-A), drilled from early May to late August 2014, and is complemented by a detailed operational report and the data repository. (Less)
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Scientific Drilling
volume
19
pages
1 - 11
publisher
Copernicus Gesellschaft Mbh
external identifiers
  • wos:000366506400001
  • scopus:84930409605
ISSN
1816-8957
DOI
10.5194/sd-19-1-2015
language
English
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yes
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c4ac751e-1ae5-4115-ab41-43f7023be31c (old id 8556686)
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2016-01-26 14:53:33
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2017-07-30 04:18:40
@article{c4ac751e-1ae5-4115-ab41-43f7023be31c,
  abstract     = {The Collisional Orogeny in the Scandinavian Caledonides (COSC) scientific drilling project focuses on mountain building processes in a major mid-Palaeozoic orogen in western Scandinavia and its comparison with modern analogues. The project investigates the subduction-generated Seve Nape Complex. These in part under ultra-high-pressure conditions metamorphosed outer continental margin and continent-ocean transition zone assemblages were emplaced onto the Baltoscandian platform and there influenced the underlying allochthons and the basement. COSC-1 is the first of two ca. 2.5 km deep, fully cored drill holes located in the vicinity of the abandoned Froa mine, close to the town of Are in Jamtland, central Sweden. It sampled a thick section of the lower part of the Seve Complex and was planned to penetrate its basal thrust zone into the underlying lower-grade metamorphosed allochthon. The drill hole reached a depth of 2495.8m and nearly 100% core recovery was achieved. Although planning was based on existing geological mapping and new high-resolution seismic surveys, the drilling resulted in some surprises: the Lower Seve Nappe proved to be composed of rather homogenous gneisses, with only subordinate mafic bodies, and its basal thrust zone was unexpectedly thick (>800 m). The drill hole did not penetrate the bottom of the thrust zone. However, lower-grade metasedimentary rocks were encountered in the lowermost part of the drill hole together with garnetiferous mylonites tens of metres thick. The tectonostratigraphic position is still unclear, and geological and geophysical interpretations are under revision. The compact gneisses host only eight fluid conducting zones of limited transmissivity between 300m and total depth. Downhole measurements suggest an uncorrected average geothermal gradient of similar to 20 degrees C km(-1). This paper summarizes the operations and preliminary results from COSC-1 (ICDP 5054-1-A), drilled from early May to late August 2014, and is complemented by a detailed operational report and the data repository.},
  author       = {Lorenz, H. and Rosberg, J. -E. and Juhlin, C. and Bjelm, Leif and Almqvist, B. S. G. and Berthet, T. and Conze, R. and Gee, D. G. and Klonowska, I. and Pascal, C. and Pedersen, K. and Roberts, N. M. W. and Tsang, C. -F.},
  issn         = {1816-8957},
  language     = {eng},
  pages        = {1--11},
  publisher    = {Copernicus Gesellschaft Mbh},
  series       = {Scientific Drilling},
  title        = {COSC-1 - drilling of a subduction-related allochthon in the Palaeozoic Caledonide orogen of Scandinavia},
  url          = {http://dx.doi.org/10.5194/sd-19-1-2015},
  volume       = {19},
  year         = {2015},
}