SUTURES AND SUTURE ZONES IN THE ALPINE - HIMALAYAN OROGENIC BELT

Sutures and suture zones are defined as the sites in orogenic belts wherein ancient oceanic lithosphere was subducted into the mantle, resulting in the closure of ocean basins and final welding of bounding continental masses along fold–fault belts with high strain. Suture zones are marked at the surface by ophiolites, mélanges, exhumed subduction channel assemblages and accretionary complexes, and at mantle depths by detached, high-velocity slabs. However, terminal continental collisions in most orogenic belts (i.e., Anatolian and Tibetan-Himalayan) were commonly preceded by collisions of intraoceanic arcs, seamounts, oceanic plateaus and/or microcontinents with trenches, forming protracted suture zones. These processes contribute to the complexities of suture zone anatomies along–across their strike, and to the difficulties of deciphering their evolutionary histories. Irregular geometries of collided continental margins, syn- and post-collisional strike–slip faulting, exhumation of UHP terranes, extensive post–collisional magmatism and significant crustal uplift–erosion commonly hinder our recognition of suture zones. The occurrence of mafic–ultramafic rock belts together with deformed passive margin sequences in intracontinental settings (i.e., Mesorif in NW Africa) has been shown to represent inverted rifts, rather than orogenic sutures. These examples indicate the need for refined, unequivocal criteria in defining and recognizing sutures–suture zones in the geological record. In this talk, I evaluate–define the sutures–suture zones in the Mesozoic–Cenozoic Alpine–Himalayan orogenic belt. The suture zones in the Western Alps–Northern Apennines mark the collision sites between Adria and Europe and include ophiolites derived from the downgoing Western Tethys oceanic lithosphere. The suture zones in the Mediterranean and Tibetan–Himalayan orogenic belts mark the collision sites between a series of ribbon continents (i.e., Pelagonia, Tauride) and arc–trench systems and / or Africa, Arabia and India continents. These suture zones include subduction initiation related, IAT– and boninite–containing SSZ ophiolites (Triassic, Jurassic & Cretaceous), derived from the upper plates of southward retreating (in the present coordinate system) subducting slabs within Neotethys.