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Abstract
The circular topographic structure in the Precambrian bedrock of southern Sweden which forms the site of Lake Mien has been interpreted to be either the result of volcanic activity or of a meteorite impact. K—Ar dating of glass and whole-rock samples suggest an age of 110–120 m.y., which cannot be related to any clearly established volcanic activity in southern Sweden during the Cretaceous. Rb and Sr analysis and Sr-isotope composition convincingly indicate that the lava-like rocks and breccias at Lake Mien have been formed by melting of the country rock.