Herbert Henkel1, Vaino Puura2, Tom Floden3, Juho Kirs2, Mare Konsa4, Ulla Preeden2, Robert Lilljequist5 and Joanne Fernlund1
1Royal Institute of Technology, Department of Land and Water Resources Engineering, S-10044 Stockholm, Sweden ([email protected])
2Institute of Geology, University of Tartu, Vanemuise 46, EE-51014 Tartu, Estonia ([email protected])
^Department of Geology and Geochemistry, Stockholm University, S-10691 Stockholm, Sweden ([email protected])
4Institute of Geology, Tallinn Technical University, Estonia pst.7, EE-10143 Tallinn, Estonia ([email protected])
5Ecominas, Calle Horno 9, Estepuma, Spain ([email protected])
Abstract. Avike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnian Sea, northeast of Sundsvall. The structure has a diameter of about 10 km. It was classified as a probable impact structure because of its extraordinary circular topography in the overwiew of impact structures in Fennoscandia. Recent studies lend further support to this interpretation. The structure has a submarine central mound, which is elevated some 40 m above the adjacent sea floor. It has a very distinct tangential and radial on-shore fracture pattern as seen in the topographic map. Along the southwestern shore of the Bay, an enigmatic quartzite breccia of unknown age occurs as part of a larger outcrop of polymict breccia with clasts of crystalline rocks and quartzite of unknown age. In thin section, planar fractures can be observed in quartz and feldspar grains. A detailed investigation showed that in a few cases the quartz grains contained microdeformation features closely resembling PDFs.
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