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Name

KEURUSSELKÄ

StatusProven
Country Finland
CoordinatesLat. N 62°08' Long.E 24°36'
Diameter km 14.0
Age Ma or date >=1144.0 ±10.0
Synonyms
Remarks Deeply eroded old impact structure. Well formed shatter cones can be found in outcrops.

In situ shatter cones and shocked quartz found in erratic breccia boulder where presented in Hietala 2004. Diameter of 14 km is from Hietala 2007. Diameters up to 30-40 km has been proposed. Age of 1140.0 ±10.0 in situ breccia dike (mentioned in Hietala 2007) from Schmieder 2010. However, it is not known for sure how that breccia dike is related to impact event. Dating suggest that age of the impact related features is in range 1880.0 - 1144.0 Ma.

Shocked quartz with decorated PDFs in Keurusselkä shatter cone rock was first mentioned in Raiskila 2010. Impact origin of Keurusselkä was substantiated by measuring 372 decorated PDF sets in quartz grains from in-situ shatter cone samples suggesting shock pressures up to 12-20 GPa range (Ferriére 2010a, Ferriére 2010c). That study shows that Keurusselkä is an deeply eroded impact structure.

Nature of decorated PDFs was also questioned because metamorphic L+V composition of checked fluid inclusions (Kinnunen 2010). However, one should remember that decorated PDFs are created long time after the impact when amorphous quartz in PDFs is healing in normal geological conditions. So you are not supposed to find any anomalities in fluid inclusions content because impact. They are only showing conditions when PDFs healed and formed fluid inclusions. Petrology of decorated PDFs also differs from primary, secondary and pseudosecondary fluid inclusions.

Alternative explanation for shatter cones is presented (Kinnunen 2009, Kinnunen 2010). Claims was commented in Öhman 2009. Arguments agains impact generated shatter cones in Keurusselkä is based on petrographic study of shatter cone surfaces, but full meaning of findings in the study is not known yet. Study explain that features were formed during slow non-impact processes.
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References
Ferriére 2010a Ferriére L., Raiskila S., Osinski G.R., Pesonen L.J. and Lehtinen M., "The Keurusselkä Sturcture (Finland) - Impact Origin Confirmed by Universalstage Characterization of Planar Deformation Features in Quartz Grains", LPSC abstract 1072 (2010)
Ferriére 2010b Ferriére L. and Osinski G.R., "Shatter Cones and Associated Shock-induced Microdeformations in Minerals - New Investigations and Implications for Their Formation", LPSC abstract 1392 (2010)
Ferriére 2010c Ferriére L., Raiskila S., Osinksi G.R., Pesonen L.J. and Lehtinen M., "The Keurusselkä impact structure, Finland—Impact origin confirmed by characterization of planar deformation features in quartz grains", Meteoritics & Planetary Science 45, Nr 3, 434–446 (2010)
Hietala 2004 Hietala S. and Moilanen J., ''Keurusselkä on muinainen osuma'', (in Finnish), Tähdet ja avaruus magazine of Ursa astronomica association (1/2004)
Hietala 2004b Hietala S. and Moilanen J., "Keurusselkä - A new impact structure in Central Finland", LPSC XXXV (2004)
Hietala 2007 Hietala S. and Moilanen J., "Keurusselkä - Distribution of Shatter Cones", abs. LPSC XXXVIII (2007)
Kinnunen 2009 Kinnunen K.A. and Hietala S., "Keurusselän pirstekartioiden tarkastelua" in Finnish with English summary: "On shatter cones in Keurusselkä area, Central Finland", Geologi Nro 3 (2009)
Kinnunen 2010 Kinnunen A. and Hietala S., "Kerusselän rakenteet: jälkiä impaktista vai tavanomaisesta deformaatiosta" in Finnish with English summary, Geologi 1/2010 (2010)
Raiskila 2010 Raiskila S., Leväniemi H., Ruotsalainen H., Salminen J. and Pesonen L.J., "The Keuruselkä impact structure, central Finland – Geophysical observations to support the impact origin", NGF Abstracts and Proceedings, no. 1, p.151, Oslo (2010)
Ruotsalainen 2006 Ruotsalainen H.E., Hietala S., Dayioglu S., Moilanen J., Pesonen L.J. and Poutanen M., ''Keurusselkä impact structure - preliminary geophysical investigations'', Lithosphere 2006 symposium Espoo, Institute of Seismology University of Helsinki (2006)
Schmieder 2009 Schmieder M., Jourdan F., Hietala S., Moilanen J., Öhman T. and Buchner E., "A high-precision late Mesoproterozoic 40Ar/39Ar Age for the Keurusselkä Impact Structure (Finland)", 40th LPSC, abstract 1028 (2009)
Schmieder 2010a Schmieder M., Buchner E., Jourdan F., Schwarz W.H., Trieloff M., Van Soest M.C., Wartho J.-A., Hodges K.V., Moilanen J., Hietala S. and Öhman T., "Updating the Finnish Impact Cratering Record", 41st LPSC, abstract 2036 (2010)
Öhman 2009 Öhman T., "Pirstekartioista Keurusselällä ja maailmalla" in Finnish with summary in English: "Shatter cones in Keurusselkä impact structure, Finland" by Öhman T., Schmieder M., Jourdan F., Buchner E. and Raiskila S., The Geological Society of Finland, Geologi Nro 6 (2009)
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