Geology of the Early Palaeozoic Lockne impact structure, Central Sweden

Lindström, Maurits; Sturkell, Erik

doi:10.1016/0040-1951(92)90164-2

Cited by 56 publications

(58 citation statements)

References 7 publications

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“…The impact structure consists of an inner crater, 7.5 km in diameter, surrounded by an 1-2.5 km wide and up to 50 m thick brim [36,37]. The brim consists exclusively of ejected, more or less brecciated, crystalline local basement, mostly granitoids from the Revsund Suite together with lesser parts of volcanites, gneisses and dolerites [37,38]. The brim is cut by at least four resurge gullies, formed when the water rushed back into the newly formed crater [39].…”

Section: The Lockne Impact Structurementioning

confidence: 99%

Extraterrestrial chromite in the resurge deposits of the early Late Ordovician Lockne crater, central Sweden

Alwmark

Schmitz

2007

Earth and Planetary Science Letters

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The distribution of extraterrestrial chromite grains (N63 μm) has been studied in the resurge deposit of the early Late Ordovician (458 Ma) Lockne impact structure in central Sweden. A 1-kg-sample of resurge sediment from the rim of the crater is extremely rich in extraterrestrial chromite. In total the sample contains N 125 chromium spinel grains kg − 1 , most grains being chromite. Due to post-depositional alterations, the origin of several of the grains is dubious, although it is clear that the major part of the chromites is of extraterrestrial origin (N 75 grains kg − 1 ), most likely derived from the impactor. The alterations are primarily due to the hydrothermal system induced by the impactor, with zinc enrichment in the chromites as the most common characteristic. The element chemistry of the least altered chromite grains indicates that the impactor was an ordinary L chondrite. This concurs with a suggested increase in the flux of L chondritic asteroids to Earth, following the disruption of the L chondrite parent body at ca. 470 Ma. More than 170 impact craters are known from around the Earth, but only few of the impactors have been identified, mainly due to the low survival rate of projectile material. Further studies of impact craters will reveal if survival of extraterrestrial chromite is unique for the Lockne structure.

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Section: The Lockne Impact Structurementioning

confidence: 99%

Extraterrestrial chromite in the resurge deposits of the early Late Ordovician Lockne crater, central Sweden

Alwmark

Schmitz

2007

Earth and Planetary Science Letters

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“…1) are the results of impact events which occurred in an epeiric sea (Lindstrˆm and Sturkell 1992;Lindstrˆm et al 1994;Ormâ nd Lindstrˆm 2000;Lindstrˆm et al 2005) during the Caradocian (Middle Ordovician) age (Grahn et al 1996).…”

Section: Geological Backgroundmentioning

confidence: 99%

Density and magnetic susceptibility of rocks from the Lockne and Tvären marine impact structures

Törnberg

Sturkell

2005

Meteoritics &Amp; Planetary Science

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Abstract-The Lockne and Tv‰ren impact craters in Sweden formed in a marine environment during the Ordovician. The contrast in density between the impact breccias and the surrounding target rock of these two craters is significantly lower than what has been found in craters formed in crystalline targets on land. Another marine-target structure, the Estonian K‰rdla structure, demonstrates intermediate contrast in impact breccia and target rock, which we attribute to the interpreted shallowness of the sea at the K‰rdla impact site. We conclude that the main cause for these low-density contrasts is pore and fracture filling of calcite with subordinate quartz and fluorite. Calcite is the most abundant cement, and its density differs most from that of fractured and brecciated bedrock with a low degree of cementation. Furthermore, from the studied cases, it is concluded that the target rock to impact rock contrast is generally the highest in craters formed on land in crystalline targets and the lowest in craters formed at sea, while craters formed on land in sedimentary targets are intermediate. The low density contrasts should decrease the negative gravity anomalies of marine craters.

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“…Three types of impactites are distinguished at Lockne, namely Tandsbyn breccia (Lindström and Sturkell 1992), Lockne breccia (Lindström et al 1983), and Loftarstone (Simon 1987). Tandsbyn breccia is a monomictic crystalline breccia of the inner crater and the brim zone (overturned flap).…”

Section: Geological Mapping Campaignmentioning

confidence: 99%

Coupled effects of impact and orogeny: Is the marine Lockne crater, Sweden, pristine?

Kenkmann¹,

Kiebach

Rosenau

et al. 2007

Meteorit & Planetary Scien

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Abstract-Our current understanding of marine-impact cratering processes is partly inferred from the geological structure of the Lockne crater. We present results of a mapping campaign and structural data indicating that this crater is not pristine. In the western part of the crater, pre-impact, impact, and post-impact rocks are incorporated in Caledonian thrust slices and are subjected to folding and faulting. A nappe outlier in the central crater depression is a relic of the Caledonian nappe cover that reached a thickness of more than 5 km. The overthrusted crater is gently deformed. Strike of strata and trend of fold axes deviate from standard Caledonian directions (northeast-southwest). Radially oriented crater depressions, which were previously regarded as marine resurge gullies formed when resurging seawater erosively cut through the crater brim, are interpreted to be open synclines in which resurge deposits were better preserved. The presence of the impact structure influenced orogenesis due to morphological and lithological anomalies of the crater: i) a raised crater brim zone acted as an obstacle during nappe propagation, (ii) the occurrence of a central crater depression caused downward sagging of nappes, and (iii) the lack of an appropriate detachment horizon (alum shale) within the crater led to an enhanced mechanical coupling and internal deformation of the nappe and the overthrusted foreland. Preliminary results of 3-D-analogue experiments suggest that a circular high-friction zone representing the crater locally hinders nappe propagation and initiates a circumferentially striking ramp fault that delineates the crater. Crustal shortening is also partitioned into the crater basement and decreases laterally outward. Deformation of the foreland affected the geometry of the detachment and could be associated with the activation of a deeper detachment horizon beneath the crater. Strain gradients both vertically and horizontally result in non-plane strain deformation in the vicinity of the crater. The strain tensors in the hanging and foot walls may deviate up to 90° from each other and rotated by up to 45° with respect to the standard regional orientation. The observed deflection of strata and fold axes within the Lockne crater area as revealed by field mapping is in agreement with the pattern of strain partitioning shown in the analogue models.

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Geology of the Early Palaeozoic Lockne impact structure, Central Sweden

Cited by 56 publications

References 7 publications

Extraterrestrial chromite in the resurge deposits of the early Late Ordovician Lockne crater, central Sweden

Extraterrestrial chromite in the resurge deposits of the early Late Ordovician Lockne crater, central Sweden

Density and magnetic susceptibility of rocks from the Lockne and Tvären marine impact structures

Coupled effects of impact and orogeny: Is the marine Lockne crater, Sweden, pristine?

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