40Ar-39Ar ages of scandinavian impact structures: I Mien and Siljan

Bottomley, R. J.; York, Derek; Grieve, R. A. F.

doi:10.1007/bf00375448

Cited by 84 publications

(22 citation statements)

References 18 publications

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“…This melt rock cuts across granite as well as a mafic dike. On the basis of published geographic information, it would not be impossible that this melt rock could represent the same material dated by Bottomley et al (1978Bottomley et al ( , 1990. It comprises an extremely fine-grained matrix that, in reflected light, appears fully crystalline (Figs.…”

Section: Samplesmentioning

confidence: 86%

“…Pseudotachylitic breccias ) of both doleritic and granitic composition have been reported (Collini 1988). According to BodÈn and Eriksson, a sample of the former was used by Bottomley et al (1978) for dating. Two of us (WUR, HH) observed millimeter-thick melt-like covers on slickensides as well as veinlets of pseudotachylitic breccia in a limestone quarry near Kallholen in the northwestern part of the ring of Paleozoic strata.…”

Section: Geology Of the Siljan Impact Structurementioning

confidence: 99%

“…Some impact-related hydrothermal Pb-Zn mineralization does, however, occur, and has been mined locally (e.g., Reimold et al 2005 and references therein; Hode et al 2002). Bottomley et al (1978) referred to an outcrop with a "small dikelet [of melt breccia] at shatter cone locality 3 of Svensson (1973)." Two samples from this site were described as containing 30-25% inclusions, predominantly quartz that occasionally shows shock deformation, but also with clasts of feldspar and brecciated granite with incipient recrystallization and rare inclusions of sandstone.…”

Section: Introductionmentioning

confidence: 99%

“…The second yielded a similar pattern but with a three-step plateau comprising 92% of release, but only because the analytical error on the middle step was 4.5% (around 10 times the two adjacent plateau steps). Re-analysis of the Bottomley et al (1978) data using ISOPLOT (Ludwig 1999) yields an age of 358.3 ± 4.8 Ma (2 σ). In addition, the final age quoted by Bottomley et al (1978) was quoted at the 1 σ level and was not the plateau age but an integrated total fusion age, in effect a K-Ar age.…”

Section: Introductionmentioning

confidence: 99%

“…Re-analysis of the Bottomley et al (1978) data using ISOPLOT (Ludwig 1999) yields an age of 358.3 ± 4.8 Ma (2 σ). In addition, the final age quoted by Bottomley et al (1978) was quoted at the 1 σ level and was not the plateau age but an integrated total fusion age, in effect a K-Ar age. It is well documented that fine-grained whole rock samples showing younger ages in the highest temperature release result from 39 Ar recoil (McDougall and Harrison 1999) and are more likely obtained from altered samples.…”

Section: Introductionmentioning

confidence: 99%

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Laser argon dating of melt breccias from the Siljan impact structure, Sweden: Implications for a possible relationship to Late Devonian extinction events

Reimold

Kelley

Sherlock

et al. 2005

Meteoritics &Amp; Planetary Science

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Abstract-In earlier studies, the 65-75 km diameter Siljan impact structure in Sweden has been linked to the Late Devonian mass extinction event. The Siljan impact event has previously been dated by KAr and Ar-Ar chronology at 342-368 Ma, with the commonly quoted age being 362.7 ± 2.2 Ma (2 σ, recalculated using currently accepted decay constants). Until recently, the accepted age for the Frasnian/Famennian boundary and associated extinction event was 364 Ma, which is within error limits of this earlier Siljan age. Here we report new Ar-Ar ages extracted by laser spot and laser step heating techniques for several melt breccia samples from Siljan (interpreted to be impact melt breccia). The analytical results show some scatter, which is greater in samples with more extensive alteration; these samples generally yield younger ages. The two samples with the least alteration yield the most reproducible weighted mean ages: one yielded a laser spot age of 377.2 ± 2.5 Ma (95% confidence limits) and the other yielded both a laser spot age of 376.1 ± 2.8 Ma (95% confidence limits) and a laser stepped heating plateau age over 70.6% 39 Ar release of 377.5 ± 2.4 Ma (2 σ). Our conservative estimate for the age of Siljan is 377 ± 2 Ma (95% confidence limits), which is significantly different from both the previously accepted age for the Frasnian/Famennian (F/F) boundary and the previously quoted age of Siljan. However, the age of the F/F boundary has recently been revised to 374.5 ± 2.6 Ma by the International Commission for Stratigraphy, which is, within error, the same as our new age. However, the currently available age data are not proof that there was a connection between the Siljan impact event and the F/F boundary extinction. This new result highlights the dual problems of dating meteorite impacts where fine-grained melt rocks are often all that can be isotopically dated, and constraining the absolute age of biostratigraphic boundaries, which can only be constrained by age extrapolation. Further work is required to develop and improve the terrestrial impact age record and test whether or not the terrestrial impact flux increased significantly at certain times, perhaps resulting in major extinction events in Earth's biostratigraphic record.

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Section: Samplesmentioning

confidence: 86%

Section: Geology Of the Siljan Impact Structurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Laser argon dating of melt breccias from the Siljan impact structure, Sweden: Implications for a possible relationship to Late Devonian extinction events

Reimold

Kelley

Sherlock

et al. 2005

Meteoritics &Amp; Planetary Science

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Settings of Meteorite Impact Structures in the Svecofennian Crustal Domain

Puura

Plado

Impact Studies

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Geophysical Investigations of the Siljan Impact Structure — A Short Review

Henkel

Aaro

Impact Studies

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Abstract. Siljan in southwest Sweden is the largest impact structure in western Europe, with a present topographic diameter of ca. 75 km. Recent age determinations indicate an age of 377 Ma. The bedrock geology of the region has recently been re-mapped by the Geological Survey of Sweden in the scale of 1:50 000. There is now complete coverage with airborne geophysics. New maps of the geophysical data have been prepared for this review. In connection with the Deep Gas Project, further geophysical studies were made and two drill holes were sunk to over 6 km depth in the central uplift of the structure. The Deep Gas Project produced a large number of reports and publications, which are listed in the summary report of Juhlin (1991). Some of the results are compiled and shortly summarized here. Digital elevation data are available with 50 m spatial resolution, and a gray tone map has been prepared with the regional trend removed. A profile of these data shows that the peak ring of the structure is still visible in the morphology.

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40Ar-39Ar ages of scandinavian impact structures: I Mien and Siljan

Cited by 84 publications

References 18 publications

Laser argon dating of melt breccias from the Siljan impact structure, Sweden: Implications for a possible relationship to Late Devonian extinction events

Laser argon dating of melt breccias from the Siljan impact structure, Sweden: Implications for a possible relationship to Late Devonian extinction events

Settings of Meteorite Impact Structures in the Svecofennian Crustal Domain

Geophysical Investigations of the Siljan Impact Structure — A Short Review

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