Open AccessPalaeomagnetism and the Siljan impact structure, central Sweden
Author(s) -
Elming StenÅke,
Bylund Göran
Publication year - 1991
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1991.tb00810.x
Subject(s) - remanence , geology , natural remanent magnetization , impact structure , impact crater , paleomagnetism , thermoremanent magnetization , coercivity , tectonics , devonian , geochemistry , magnetization , mineralogy , seismology , geophysics , astrobiology , condensed matter physics , physics , quantum mechanics , magnetic field
SUMMARY The Siljan impact structure (diameter c. 52 km) located in central Sweden, is considered the largest meteorite crater in Western Europe. The time of impact has been estimated to be 368 Ma from Ar‐Ar dating of an impact melt. A palaeomagnetic study of rocks, from inside and outside the impact structure has been carried out, with the aim of identifying natural remanent magnetizations (NRMs) related to the impact event. Primary magnetizations are partly preserved within the impact area. However, the directions of these original magnetizations are disturbed due to tectonic movements related to the impact. Three different directions of magnetizations, not recognized elsewhere, were identified within the central part of the structure. These three magnetizations are defined in order of increasing coercivity ( H C ) and blocking temperature ( T B ). The origin of a high‐ H C chemical remanent magnetization (CRM) (C) of late Palaeozoic time carried by haematite can be interpreted as due to oxidation caused by circulating meteoric water in cracks and fractures caused by the impact. Another component, (B) identified in a lower temperature range, (40d̀‐580d̀C) is probably carried by magnetite. In pseudotachylite this magnetization is considered as a thermal remanent magnetization while in other rocks its pre‐tectonic character and occurrence also in the low‐coercivity range implies a shock remanent origin. The palaeomagnetic pole for this remanence corresponds to a Silurian‐Devonian age, which gives an age of impact which is not very diffirent from that estimated by radiometric data. A third low‐ H C and T B component (A) is interpreted to be a CRM carried by slowly growing goethite. The direction of this CRM implies it to be a recent post‐impact magnetization.