Impact-related hydrothermal activity in the Lockne impact structure, Jamtland, Sweden

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doi: 10.1127/ejm/10/3/0589
Authors:Sturkell, Erik F. F.; Broman, Curt; Forsberg, Per; Torssander, Peter
Author Affiliations:Primary:
Stockholm University, Department of Geology and Geochemistry, Stockholm, Sweden
Volume Title:European Journal of Mineralogy
Source:European Journal of Mineralogy, 10(3), p.589-606. Publisher: Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller), Stuttgart, Federal Republic of Germany. ISSN: 0935-1221
Publication Date:1998
Note:In English. 54 refs.; illus., incl. 1 table, geol. sketch map
Summary:The Lockne impact structure in central Sweden was formed ∼ 455 m.y. ago (Middle Ordovician) in a marine environment, at a sea-water depth of ≥ 200 m; the water depth in the centre of the resulting crater with a diameter of 13.5 km was ≥ 500 m. The area was affected by Caledonian overthrusting and associated low-grade thermal metamorphism to ≤ 300°C, as shown by the degree of crystallinity of black-shale graphite, conodont-alteration colour and the presence of laumontite. The clasts in the impact breccia were initially rich in cavities that were later filled with calcite and other minerals; fluid inclusions in the cavity minerals are mainly hydrocarbons and brine. The earliest fluid is believed to have been derived from an organic-rich Cambrian clay flowing into the crater during the resurge phase, and thermally altered by the residual heat of the impact, which also generated a hydrothermal convection system. Calcite and sulphides deposited in breccia cavities indicate a brine with salinity ∼ 20 % eq. CaCl2 at 210°C; δ 13C for calcite is -2 to -14 0/00, indicating mixing with an organic source, and δ 18O is +10 to +14 0/00, perhaps indicating a meteoric or sea-water source. [R.A.H.]
Sections:Meteorites and tektites
Subjects:C-13/C-12; Carbon; Fluid inclusions; Hydrocarbons; Hydrothermal conditions; Inclusions; Isotope ratios; Isotopes; Middle Ordovician; O-18/O-16; Ordovician; Organic compounds; Oxygen; Paleozoic; S-34/S-32; Stable isotopes; Sulfur; Europe; Jamtland Sweden; Scandinavia; Sweden; Western Europe; Lockne impact structure
Coordinates:N630000 N630000 E0144930 E0144930
Abstract Numbers:98M/4081
Record ID:1998046915
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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