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4. Locations

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Location No. 17

Outcrop at the northern coast of Skälö. Approach via road from Västrum to the northern part of Skälo. Walk behind the eastern side of the bridge. Be careful, wet rocks are slippery!

R: 1548032 - H: 6386204
RT 90: N 57° 35' 55.2" - E 016° 36' 42.1"
WGS 84: N 57° 35' 54.1" - E 016° 36' 31.4"

Keywords: metabasites, basic flows


Description:

In the area around Skälö basic volcanites are intercalated within the felsic metasediments of the Västervik Formation. They mainly strike NW-SE concordant to the surrounding rocks. At this location the rocks are black colored, dense and fine-grained with visible layering and flow fabric. Numerous bubbles, some of them filled with secondary minerals, are striking (cf. fig. 4.17a-d). According to Reifferscheidt (1996), the main components of this basic rock are hornblende, biotite, quartz, ores and plagioclase. It has been discussed whether they should be interpreted as sills or flows. Following criteria point to basic flows:

A contact zone with apophyses can only be found at one side of these rocks, the footwall. The rocks show an asymmetric zonation with bubbles of different sizes (cf. fig. 4.17b-c). This can be ascribed to degassing processes under different pressure conditions, that depend on the closeness to the surface. The closer to the surface the bigger the bubbles are developed. This matter of fact can also be used as identification of the hanging walls and footwalls. It is also possible to count several sequenced flows on this criteria. In his studies Kresten (1972) assigned these rocks to the first generation of basic magmatism.



Further Reading:

Kresten, P., 1972. Der basische Magmatismus und seine Stellung in der geologischen Entwicklung des Västervik-Gebietes, Südostschweden, GFF, 94, 91-109.



Fig. 4.17a: Partial over view of the outcrop showing polished rocks and layers with bubbles. (Photo: K. Wemmer, pers. comm.)
Fig. 4.17b & c: Close up views show grading of the bubbles; small at the bottom and growing bigger upwards. Some bubbles are filled with minerals.
Fig. 4.17d: Close up view of the basic flow shows bubbles that are partly filled with minerals.


(top)

Fig. 4.17a
Fig. 4.17a

Fig. 4.17b
Fig. 4.17b

Fig. 4.17c
Fig. 4.17c

Fig. 4.17d
Fig. 4.17d
 

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