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4. Locations

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Location No. 06

Roadcut on the eastern wall along highway E22 about 2.4 km northeast of the exit to Gunnebo. Park in a parking bay about 100 m north of the outcrop. For preservation of the limited amount of material please refrain from taking any samples!

R: 1544274 - H: 6401826

Keywords: sedimentary dyke, granodiorite


The roadcut on highway E22 shows a 3 to 5 cm thick sedimentary dike, which is steeply inclined and strikes almost N-S (cf. fig. 4.6a). It is not possible to track the dike in the surroundings of the outcrop.

The host rock is a granodiorite, which according to a description by Gavelin (1984) belongs to the older granitoids. The granodiorite is dark and coarse-grained without any visible foliation. Big red alkali feldspar phenocrysts cause the porphyry fabric. Other main components are white, medium to coarse-grained plagioclase and fine-grained quartz. The mafic fraction with a percentage of 20 - 25 % is mainly biotite, which accumulated in cm to dm large round or ovoid mafic enclaves. They may be interpreted as former drops of a magma mixing phenomenon. Behind the bridge the wall on the opposite side of the road shows an enriched area of deformed mafic blobs within the rock (cf. fig. 4.6f).

The sedimentary dike contains a lot of detrial components. According to a description by Jacke & Vollbrecht (2004) rock fragments are mainly from the surrounding granitic rocks. Overall the main part of the dike is the monomineralic detritus. It contains mainly well-rounded quartz grains (cf. fig. 4.6b-d). Many of them have zircon, biotite, gas or fluid inclusions. The feldspar grains, in minor frequency, are subangular in shape. Fresh plagioclases and alkali feldspars often have inclusions of biotite, zircon and rutile. Biotite, zircon, rutile and apatite grains only occur as minor components. The sedimentary dike is consolidated by a calcite cement and a clay-silt matrix. Jacke & Vollbrecht (2004) described several stages for the development of this dike (cf. fig. 4.6e).

This and other sedimentary dikes within the Västervik area, as well as others found in Denmark and Finland, are supposed to be of early Cambrian age and can be related to an extensional environment at that time. Which consequently means that the Proterozoic surface already must have been eroded to a surface level in which fissures in granitoids could be filled with sediments.

Further Reading:

Bergman, L., 1982. Clastic dikes in the Åland Islands, SW Finland and their origin. In L. Bergman, R. Tynni & B. Winterhalter (eds.): Paleozoic sediments in the Rapakivi area of the Åland Islands. - Bull. Geol. Soc. Finland, 317: pp 8 - 32.

Katzung, G. & Obst, K., 1997. The sandstone dike swarm of Vang, Bornholm -8Denmark). - Bulletin of the Geological Society of Denmark, Vol. 44: pp. 161-171.

Tynni, R.,1982. On Paleozoic microfossils in clastic dikes in the Åland Islands and in the core samples of Lumparn. In L. Bergman, R. Tynni & B. Winterhalter (eds.): Paleozoic sediments in the Rapakivi area of the Åland Islands. - Bull. Geol. Soc. Finland, 317: pp 8 - 32.

Jacke, O. & Vollbrecht, A., 2004. Sedimentgänge in proterozoischen Graniten der Västervik-Region (SE-Schweden), Terra Nostra 2004/01, TSK X: 10. Symposium Tektonik, Struktur- und Kristallingeologie, Aachen, 31.03. - 02.04.2004, Abstr.: 35.

Fig. 4.6a: Partial view of the sedimentary dike. (Photo: A. Vollbrecht, pers. comm.)
Fig. 4.6b: Close up view of a polished piece from the sedimentary dike showing fractures from the granitic host rock. (Photo: O. Jacke, pers. comm.)
Fig. 4.6c: Partial view of a thin section exhibiting rounded quartz grains in a calcite matrix. (Photo: O. Jacke, pers. comm.)
Fig. 4.6d: Close up view of a polished piece from the sedimentary dike showing a surging fabric. (Photo: O. Jacke, pers. comm.)
Fig. 4.6e: Schematic model of the development of the sedimentary dike: 1 - initial formation of sub-vertical tension cracks. 2 - lateral extension and filling with rock fragments and detrial grains. 3 - further extension caused a suction effect leading to downward dragging of the unconsolidated fillings. 4 - consolidation of vein fillings due to mechanical compaction and pressure solution. 5 - multiple-phase opening and healing of the cracks with calcite. 6 - another formation of fissures, filling with new sediments and brecciation of former consolidated detritus and calcite veins. 7 - further extension and surging of the latest soft sediments caused a preferred orientation of the calcite fragments parallel to the dike wall. (Model: Vollbrecht, A. & Jacke, O., (in prep.))
Fig. 4.6f: Partial view of deformed mafic blobs in a granitic host rock. (Photo: B. Leiss, pers. comm.)


Fig. 4.6a
Fig. 4.6a

Fig. 4.6b
Fig. 4.6b

Fig. 4.6c
Fig. 4.6c

Fig. 4.6d
Fig. 4.6d

Fig. 4.6e
Fig. 4.6e

Fig. 4.6f
Fig. 4.6f

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