COLLISION-INDUCED SLAB BREAKOFF, LITHOSPHERIC TEARING AND RELATED MAGMATISM IN CENOZOIC ANATOLIA, AND COMPARISON WITH OTHER OROGENIC BELTS

Subduction of the Tethyan mantle lithosphere northward beneath Eurasia was continuous since the latest Cretaceous, only temporarily punctuated by the accretion of ribbon continents & by slab breakoff events. Exhumation of middle-lower crustal rocks & the formation of extensional domes occurred in the backarc region of this progressively southward-migrated trench & the Tethyan slab throughout the Cenozoic. Continental collisions following the closure of Tethyan seaways led to crustal thickening, slab breakoff, delamination & lithospheric tearing that resulted in lateral mantle flow, lithospheric extension & accompanying magmatism. Initial stages of post-collisional magmatism (~45 Ma) thermally weakened the orogenic crust, causing large-scale extension & lower crustal exhumation via core complex formation around 25-23 Ma. Slab breakoff was the most common driving force for the early stages of post-collisional magmatism. Magmatic rocks produced at this stage are represented by calc-alkaline–shoshonitic to transitional igneous suites. Subsequent lithospheric delamination or partial convective removal of the sub-continental lithospheric mantle caused decompressional melting of the upwelling asthenosphere that produced alkaline magmatism (<12 Ma). Attendant crustal extension & widespread thinning of the lithosphere facilitated rapid ascent of basaltic (OIB) melts & hence the eruption of asthenosphere-derived magmas. The subduction of the modern African lithospheric slab beneath the Aegean-Western Anatolian region is delimited to the E by a subduction-transform edge propagator (STEP) fault, which corresponds to the sharp cusp between the Hellenic & Cyprus trenches. This lithospheric tear in the downgoing African plate allowed the mantle to rise beneath SW Anatolia, inducing decompressional melting of shallow asthenosphere & producing linearly distributed alkaline magmatism, younging southward in the direction of tear propagation. The N-S-trending potassic & ultra-potassic volcanic fields stretching from the Kirka & Afyon-Suhut region (~17 Ma) in the N to the Isparta-Gölcük area (4.6 Ma–Recent) in the S are the result of this melting of the sub-slab mantle. Comparison with some other collisional orogenic belts shows a similar pattern of tectonic events & magmatic response through time.