Duobblon is a 50 to 80 km diameter structure of which a ca. 30 km long and 5 km wide segment is preserved containing polymict brecciated rocks and suggested suevite. The structure is partly hidden under Caledonian thrusted units and has an age of less than 1.87 Ma (which is the age of one of the target rocks). The structure has been extensively drilled for mineral resources.
References:
Lilljequist, R., and Preeden, U., 2005: The Duobblon structure – A small segment of a large Precambrian impact structure? In: C.Koeberl and H. Henkel (eds) Impact Tectonics, Springer Verlag ISBN 3-540-24181-7: 307-322