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Shock metamorphism and hydrothermal alteration of mafic impact ejecta from the Lockne impact structure, Sweden
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Number of Authors: 7
2017 (English)In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 139, no 2, 119-128 p.Article in journal (Refereed) Published
Abstract [en]

The local geology at Kloxasen is characterised by ejecta deposits from the 458 Ma Lockne marine impact. The Kloxasen ejecta are located on a Caledonian parautochthonous unit, approximately 7 km from the centre of the 7.5-km-wide Lockne crater structure. The ejecta were deposited on the seafloor and were covered with seawater immediately after the impact event. Of special interest is a mafic impact breccia within the ejecta, which before the impact was angstrom sby dolerite that belongs to the Jamtland suite of the 1.25 Ga Central Scandinavian Dolerite Group. The mafic impact breccia occurs mainly as a coherent thin domain within a larger block of granitic breccia, which we interpret as a result of the in situ brecciation of a dolerite sill within granitic bedrock. Shock pressure in the doleritic breccia was low, in the order of 0.4 GPa, constrained by the presence of mechanically twinned clinopyroxene. Low shock pressure and brecciation corresponds well to the spall zone of an impact crater, where ejecta originate from. Whereas spalled ejecta can also show signs of having been exposed to high shock pressures, including shocked quartz, evidence for this was not found in the Kloxasen ejecta. The breccia has been hydrothermally altered, but the ejecta are too far removed from the crater to have been affected by hydrothermal circulation in relation to Lockne's impact event. Fluid inclusion analyses suggest that most of the alteration happened later, during the Caledonian orogeny. Geochemical analyses reflect observed mineral alterations well, such as serpentinisation of olivine.

Place, publisher, year, edition, pages
2017. Vol. 139, no 2, 119-128 p.
Keyword [en]
Mafic impact ejecta, Lockne impact structure, shock metamorphism, hydrothermal alteration
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-144616DOI: 10.1080/11035897.2016.1227361ISI: 000400818800003OAI: oai:DiVA.org:su-144616DiVA: diva2:1115205
Available from: 2017-06-26 Created: 2017-06-26 Last updated: 2017-06-26Bibliographically approved

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CiteExportLink to record
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Citation style
  • apa
  • harvard1
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  • modern-language-association-8th-edition
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More styles
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  • de-DE
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