COMPLEX MORPHOLOGY OF COLLIDING MARGINS IN LAURUSSIA-GONDWANA SUPERCOLLISION

Late Paleozoic convergence between Gondwana and Laurussia culminated in terminal collisions that produced the Ouachita-Alleghanian-Mauritanian-Variscan orogen within the interior of Pangea. The evolution and architecture of this orogen was profoundly influenced by a series of ca. 400-300 Ma promontory collisions, which terminated 100 m.y. of subduction and terrane accretion along the Laurussian margin and passive margin sedimentation along the Gondwanan margin. These promontory collisions compartmentalized the orogen into several domains with very different subsequent tectonic evolutions. In Europe, the Variscan belt records coeval collisional (e.g. Iberian massif) and “Mediterranean-style” orogens (e.g. Bohemian massif). The former are characterized by crustal thickening, followed by extensional collapse. The latter occur in re-entrants and are characterized by complex orogenic collages of limited lateral extent produced by the opening and closing of ephemeral oceans. This collage includes the products of subduction of varying polarities within these oceans and accretionary collisions of local significance that preceded terminal collision. Late-stage orogenic processes are characterized by the formation of oroclines, extensional collapse, and the transition to Tethyan tectonics. Because part of the Laurentian-Mauritanide domains were located to the southwest of the promontory collisions, remnants of the Rheic Ocean persisted between them and their respective evolutions, as recorded in the Appalachian belt, are dominated by Andean-style orogenesis that preceded terminal collision.

The geodynamic driver of Pangea amalgamation, by the Appalachian-Mauritanide-Variscan orogen, is consistent with the principles of orthoversion. In other collisional orogens, determining when geological continuity along converging continental margins gives way to compartmentalization may likewise document when promontory collisions have occurred.