The Duobblon Structure - A Small Segment of a Large Precambrian Impact Structure?

The Duobblon Structure is located in northern Sweden, near the Scandinavian mountain range in the county of Västerbotten. The structure constitutes a 30 km long formation, slightly concave to the NW. The Revsund Granite (1.87 Ga) makes up most of the basement, and grades into a 100 m thick autochthonous basal breccia, overlain by a chert-like, clast-bearing melt rock and a polymict breccia. A fine-grained volcanic-like rock makes up the top of the series. Caledonian nappes of Cambro-Silurian age covers the structure to the W. The possible presence of planar deformation features in quartz and the similarity to the stratigraphy of proven complex impact structures support a possible impact origin. The age of the assumed impact event might correspond to a U-Pb zircon age of about 1.80 Ga, which is the indicated age of a chert-like rock in-between the autochthonous and the polymict breccia. Assuming that the arcuate breccia formations form part of a once circular structure, a crater diameter of approximately 80 km can be inferred, of which 1/7 of the outer margin is preserved