GEOLOGICAL AND GEOCHEMICAL CONSTRAINTS ON THE NORTHWARD PROPAGATED OCEAN BASIN EVOLUTION AND SUPRA-SUBDUCTION ZONE TYPE OPHIOLITE IN THE ISPARTA ANGLE AREA, SW TURKEY

Allochthonous assemblage in the northern part of the Antalya Complex in SW Turkey is mainly characterized by slope basin deposits associated with late Triassic alkaline volcanic units. These volcanic rocks range in composition from alkali basalt with high-Ti (TiO₂>2) to fractionated trachyandesite with low-Ti (TiO₂<2), late Jurassic-early Cretaceous tholeiitic volcanic rocks varying in the composition from basaltic to rhyolitic, and Cretaceous tholeiitic MORB-type volcanics. The MORB-type volcanic units are spatially associated with serpentinites, deep basin deposits and arc-type mantle peridotites (Egridir Kizildag peridotites) which are intruded by thloeiitic isolated diabasic dykes. Mantle peridotites represented by harzburgitic mantle tectonites with minor dunite have high MgO varying between 42.15-45.61 wt%, Mg# values (90.52-91.45) and low to very low contents of Al₂O₃ (0.32-0.97 wt%), CaO (0.47-1.31 wt%). The isolated dykes intruding the Kizildag peridotite show flat REE patterns with relatively low (La/Yb)n ratios (0.57<(La/Yb)n<0.68), consistent with N-MORB composition. Depletion in LREE indicates that the melt that formed isolated diabasic dykes was generated from a mantle source depleted by previous melt extraction. The geochemical data from the mantle peridotites and the isolated diabasic dykes indicate that the Late Cretaceous ophiolites in the northern part of the Antalya Complex (in the south of Egridir Lake) developed in a suprasubduction zone setting. The change from alkaline to transitional and tholeiitic MORB-type composition reflects evolution of continental rift into an oceanic rift, as in the present-day Red-Sea example. Late Triassic alkaline volcanics in the north of Antalya Complex are associated with rift-related deposits, whereas the Triassic alkaline volcanics in the south and in the west of Antalya Bay (Kara Dere-Sayrun unit) are associated with serpentinites. Also, the Triassic alkaline lavas in the west of Antalya Bay are interlayered with thin, pelagic limestone layers. To the further south, in the Mamonia Complex (SW of present Cyprus Island), late Triassic volcanics which represents the remnants of intra-oceanic island volcanoes are in places overlain by late Triassic reef limestones and pelagic deposits, suggesting deepening and widening of Antalya ocean towards the Cyprus ocean in the south. These geological and geochemical data suggest a continental rifting and opening of wedge-shaped ocean basin propagated northward in the Isparta Angle area in SW Turkey.