Peritectic assemblage entrainment and mafic-felsic magma interaction in the Late Oligocene-Early Miocene Karadağ Pluton in the Biga Peninsula, northwest Turkey: petrogenesis and geodynamic implications


Abstract: The Hellenic subduction system governs the entire Aegean region through the creation of a migrating magmatic arc that has existed since the beginning of the Early Cenozoic. The Karadağ Pluton is situated in the NW part of Turkey and represents one of the distinct snapshots of this subduction system during the Late Oligocene-Early Miocene Period.iod. It consists of 2 major lithological units, based on their petrographic and geochemical features, comprising: 1) main plutonic facies (SiO2 < 70 wt.%) that are dominated by hornblende- and biotite-bearing monzogranite, quartz monzonite, and granodiorite, and 2) late-stage more felsic facies (SiO2 > 70 wt.%) that are represented by cordierite-free and cordierite-bearing leucogranites. Zircon U-Pb laser ablation inductively-coupled plasma mass spectrometry and K-Ar dating revealed crystallization and cooling ages of 23.9 ± 0.5 Ma and 20.2 ± 0.9 Ma for the main plutonic bodies, and 22.0 ± 1.1 Ma for the leucogranite facies, respectively. The pluton had a high-K calc-alkaline affinity and exhibited a metaluminous to peraluminous (aluminum saturation index of <1.1), and displayed an I-type character. It was enriched with large ion lithophile elements and light rare earth elements, and it was depleted of high field strength elements with negative Eu anomalies. In the tectonic setting discrimination diagrams, all of the granite samples fell into the volcanic arc granite and syn-collisional granite fields. The initial Sr-Nd isotope data of the pluton were compatible with an enriched mantle source. Petrographic and geochemical features indicated that it has been affected by multiple magma evolution processes, such as fractional crystallization, magma mixing, and assimilation. Moreover, the pluton displayed source heterogeneities and peritectic mineral entrainment, such as the coexistence of K-feldspar and cordierite, which could be interpreted as incongruent melting of the crust in the fluid-present system. The petrological and geochemical data suggested that the Karadağ Pluton formed by the mixing of mantle-derived mafic and crustal-derived felsic magmas at shallow crustal levels, mainly derived by the partial melting events related to the northward subduction of the Hellenic slab beneath the Sakarya Zone.

Keywords: Peritectic entrainment assemblage, magma mixing, U/Pb and K-Ar dating, mantle-crust interaction, Biga Peninsula, Sakarya Zone

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