Geology and geochemistry of the synextensional Salihli granitoid in the Menderes core complex, western Anatolia, Turkey

Abstract

The Miocene Salihli granitoid (SG) in the footwall of the Alasehir detachment in the Menderes core complex is a synextensional intrusion, providing important structural, geochronological, and geochemical constraints on the nature of late Cenozoic magmatism associated with crustal extension in the Aegean province. The NW–SE elongated pluton crosscuts the extensional mylonitic fabric in the metamorphic host rocks but is foliated, mylonitized, and cataclastically deformed in a ∼100‐m‐thick shear zone along the detachment. Mylonitic granitoids range from ultramylonites to protomylonites, and exhibit ductile deformation structures showing consistently top‐to‐the north shearing. Grain‐size reduction and dynamic recrystallization were most common deformational mechanisms producing the structural fabric of the mylonitic granitoid rocks. This earlier ductile fabric is overprinted by north‐dipping cataclastic foliation that developed sub‐parallel to the Alasehir detachment and its shear zone. Crystallization and cooling ages of the SG are nearly coeval with the documented early Miocene ages of metamorphism and deformation in its host rocks. The SG pluton ranges in composition from granite, granodiorite, and alkali‐feldspar granite, to monzogranite, and syenogranite; it consists of metaluminous to slightly peraluminous, high‐K calc‐alkaline rocks with silica contents between 62.36 and 73.95 wt‐%. The rocks are enriched in LILE and depleted in HFSE, and show strong negative anomalies in Ba, Nb, Sr, P, and Ti. These geochemical features suggest derivation of the SG melts from a subduction‐metasomatized, subcontinental lithospheric mantle. Invasion of the lower and middle crust by mantle‐derived melts triggered MASH‐type processes (melting, assimilation, storage, homogenization), resulting in the production of hybrid SG magmas. Asthenospheric upwelling caused by lithospheric delamination was a likely heat source that triggered the inferred partial melting of the mantle lithosphere. Continued extensional deformation and unroofing of the Menderes core complex and the synextensional SG in the mid to late Miocene was accompanied by the formation of an asymmetric supradetachment basin in the hanging wall of the Alasehir detachment.