Slab break-off and syncollisional origin of the Late Cretaceous magmatism in the Central Anatolian crystalline complex, Turkey

The Late Cretaceous calc-alkaline to alkaline plutons in the Central Anatolian crystalline complex are intrusive into metamorphic and ophiolitic rocks and mark a major magmatic pulse in the late Mesozoic evolution of the eastern Mediterranean region. We grouped the plutonic rocks with similar mineral and chemical compositions and inferred genetic relations into the granite, monzonite, and syenite supersuites. Granitic plutons mainly occur along the western edge of the Central Anatolian crystalline complex, whereas syenitic plutons form smaller bodies that crop out in the inner part. The granite supersuite is composed of granitic to granodioritic rocks, and the monzonite supersuite consists mainly of quartz monzonite and monzonitic rocks; both supersuites show enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE). The granitic-granodioritic rocks have compositions typical of high-K calc-alkaline and high-K shoshonitic series, whereas the monzonitic rocks display compositions characteristic of shoshonitic series. The syenite supersuite consists of quartz syenite, syenite, and nepheline- and pseudoleucite-bearing alkali rocks and shows more enrichment in LILE and a slight enrichment in HFSE compared to the other two supersuites. All three supersuite rocks have high 87Sr/86Sr and low 143Nd/144Nd ratios. These geochemical features suggest that the granite and monzonite supersuite magmas were derived from a subduction-modified and metasomatized mantle source and that the syenite supersuite magmas were derived from an enriched mantle source with considerable crustal contribution. New 40Ar/39Ar ages at 77.7 ± 0.3 Ma for the granite, 70.0 ± 1.0 Ma for the monzonite, and 69.8 ± 0.3 Ma for the syenite supersuite rocks indicate progressive evolution of the Central Anatolian crystalline complex magmatism from calc-alkaline to alkaline compositions with time. The latest Cretaceous emplacement of the complex's plutons and the chemical evolution of their magmas were syn-collisional in nature, after the leading edge of the Tauride platform collided with a trench in the Inner Tauride ocean and became partially subducted. Subsequent slab break-off resulted in asthenospheric upwelling and perturbation of the subduction-metasomatized lithospheric mantle that collectively produced the primary melts for the Central Anatolian crystalline complex plutons. These melts evolved through combined assimilation–fractional crystallization and mixing-mingling processes during their ascent and were affected by the interactions between mantle-derived and crustal-derived magmas. The late phases of this intracontinental magmatism were accompanied by tectonic extension of the thermally weakened orogenic crust in the Central Anatolian crystalline complex.