The Strymon Valley detachment system accommodated at least 25 km of extension at the northern margin of the Aegean extensional province from middle Miocene through early Pliocene time. The primary detachment surface is exposed as a gently southwest-dipping low-angle normal fault—similar to those widely known in core complex settings of the U.S. Basin and Range province—for more than 150 km along strike, from the Aegean Sea coast in northeastern Greece northward into the Struma Valley of southern Bulgaria. Hanging-wall rocks in the Strymon Valley detachment system moved in a S53°W direction relative to the footwall, resulting ultimately in the tectonic unroofing of the Rhodope metamorphic core complex. Several segments of the Strymon Valley detachment have previously been interpreted as thrust faults formed during a Miocene compressional event. Our results negate the principal evidence for this event and imply instead that extensional deformation has characterized the northern Aegean region since at least middle Miocene time.
Displacement ceased on the Strymon Valley detachment with the late Pliocene development of the Strymon and Drama basins. We propose that those basins, together with the other principal basins of the northern Aegean region, are subsiding above an active northeast-dipping, extensional detachment zone that forms a unified kinematic system with the western offshore continuation of the dextral North Anatolian strike-slip fault, the North Aegean trough. If this hypothesis is correct, then the North Aegean trough, the western strands of the North Anatolian fault, and the principal modern depocenters of the northern Aegean region may all have originated no earlier than late Pliocene time.