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4. Locations

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Location No. 03

Cliffs at the shore of Bjursund's campsite. Park in the campsite's parking area. Short walk across the campsite, right turn at the playground and walk over a small footbridge to reach the coast. This outcrop offers many details to explore.

R: 1546800 - H: 6421575
RT 90: N 57° 55' 14.1" - E 016° 36' 58.0"
WGS 84: N 57° 55' 12.9" - E 016° 36' 47.1"

Keywords: mylonites, LLDZ


Description:

This really interesting outcrop at the shoreline of Bjursund's campsite shows part of the Loftahammar-Linköping Deformation Zone (LLDZ). The matrix is extremely fine grained and light to dark gray in color. Strongly folded leucocratic and melanocratic veins, which are steeply dipping and mainly strike NW-SE, are imbedded in the matrix (cf. Fig. 4.3a,c,d). The leucocratic components mainly contain quartz and feldspar whereas the melanocratic veins mainly consist of biotite, hornblende and ore minerals. Deformed pegmatite veins and networks of younger composite dikes from mafic and granitic sources can be observed. Different shear sense indicators like shear folding and sigma clasts point to a dextral sense of shear. The polished rocks additionally show glacial striations.

The host rock of this mylonite presumably belongs to the metasedimentary Västervik formation. An example of this could be the small area of preserved metasedimentary rock adjacent to the mylonite. It shows small scale folding and visible graded bedding (cf. Fig. 4.3b).


Study Questions:
  • Find and draw a sketch of several shear sense indicators.
  • Can you detect different generations of veins/dikes?


Further Reading:

General information on the development of the LLDZ:
Beunk, F.F. & Page, L.M., 2001. Structural evolution of the accretional continental margin of the Paleoproterozoic Svecofennian orogen in southern Sweden, Tectonophysics, 339, 67-92.



Fig. 4.3a: Strongly folded vein with leuco- and melanosome shows dextral sense of shear
Fig. 4.3b: Close up view of a metasediment adjacent to the mylonites showing small scale folding and graded bedding.
Fig. 4.3c: Close up view of a composite dike. Mafic veins are disrupted by later granitic injections. (Photo: K. Wemmer, pers. comm.)
Fig. 4.3d: Close up view of a strongly folded vein with leuco- and melanosome showing dextral sense of shear.


(top)

Fig. 4.3a
Fig. 4.3a

Fig. 4.3b
Fig. 4.3b

Fig. 4.3c Fig. 4.3c

Fig. 4.3d Fig. 4.3d
 

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