Anatomy of a diffuse cryptic suture zone exemplified by European Variscan belt: a new view on the internal architecture of collisional orogens

The plate tectonics has offered a currently accepted link between the horizontal movement of lithospheric plates, closure of intervening oceanic basin and formation of oceanic suture zone preserved in continental collision zones. The Paleozoic Bohemian Massif is a classical collisional orogen evolving through Andean type convergence and for which a modified view on the internal architecture of collisional orogens was recently proposed. The characteristic feature of the new model is the convergence of two contrasting lithospheric domains related to subduction of an attenuated felsic metaigneous crust under thehigh density metabasite dominated rifted (Gondwana) margin. The relamination of refractory light material rich in radioactive elements underneath the relatively dense upper plate is responsible for the gravitational instabilities that lead to the overturns in the thickened crust. Such a process results in the formation of a diffuse cryptic suture zone, i.e., a wide zone in which materials from the lower and upper plates are mixed to form a hybrid continental crust. The diffuse cryptic suture zone remains the only evidence of the original plate boundary repeatedly re-appearing within the orogen.