Magma Interaction Processes Inferred from Fe-Ti Oxide Compositions in the Dölek and Sariçiçek Plutons, Eastern Turkey

Magnetite-ulvöspinel and ilmenite-hematite solid solution intergrowths from the high-K calc-alkalineDölek and Sarıçiçek plutons, Eastern Turkey, were investigated using microprobe analyses. Compositions of twenty-eight samples from the host rocks and their enclaves in the plutons were used to estimate the oxygen fugacity and temperature. The ilmenite and ulvöspinel component exsolves out along certain preferred crystallographic planes in the titanomagnetite of the host rocks, while they are always absent in those of the mafic microgranular enclaves. The titanomagnetite and ilmenite show variations as Mt98–70Usp02–30 and Ilm99–65Hm01–35 in composition, respectively. Estimations of oxygen fugacity and temperature using the titanomagnetite-ilmenite thermometry/oxygen barometry range from logfO2 of -15.30 to -20.48 in host rocks, logfO2 of -15.39 to -20.80 in the mafic microgranular enclaves and 617±6 to 758±23 °C in host rocks, 622±6 to 735±24 °C in the maficmicrogranular enclaves, possibly indicating crystallisation temperature. Applying magnetite-ilmenitethermometry/oxygen barometry to the granitoid rocks also involves microprobe analyses of ilmenite lamellae in titanomagnetite and this method yielded mean temperatures of 679±18 °C. The specific forms and chemical properties of Fe-Ti oxides, and similarities in crystallization temperature and oxygen fugacity of the host rocks and the mafic microgranular enclaves (MME) obtained from the Fe-Ti oxide pairs imply that thermal equilibrium probably occurred between two contrasted magmas, which mixed in various proportions so that possibly a felsic and a more mafic magma interaction occurred in a convectively dynamic magma chamber during crystallization of the plutons. Probably, underplating may be responsible for genesis of the hybrid plutons. Thus, for mixing of coeval magmas derived from a lithospheric upper mantle (mafic end-member) and lower crust (felsic endmember), a thermal anomaly should be supplied. Upwelling of hot asthenospheric material results in thermal perturbation and melting of lithospheric mantle. Intrusion of hot lithospheric mantle-derived mafic magma then induced lower crustal melting, producing felsic melt. Mixing of the lower crust-derived melt and lithosphericmantle-derived magma formed the hybrid plutons. This process requires a post-collisional extensional tectonic setting during the Eocene in the Eastern Pontides.