Geochemical and geochronological evidences from Cambrian to Ordovician protracted magmatism in the Istranca Massif, NW Türkiye

Plutonic rocks in different ages are cropted out and form the basement rocks in the Istranca Massif. One of the plutons located at the basement is the Cambrian-Ordovician Vize pluton (Vize-Kırklareli) and is distinguished from other plutons by some of its characteristic features. This pluton intruded into the high-grade metamorphic sedimentary rocks, and is unconformably overlay by Triassic low-grade metamorphic rocks and Eocene aged coral reef limestones (Soğucak Formation). Based on new whole rock geochemical and zircon UPb data concentrated in two different ages, it can be said that the Vize pluton was affected by protracted magmatic activity. The igneous minerals and texture of Vize pluton are partly preserved, It has a mylonitic texture, a distinct foliation consisting of light and dark zones. In addition, metagranites contain mafic magmatic enclaves (MMEs) in some places.

The Vize pluton is an I-type pluton with predominantly peraluminous and slightly metaluminous character. It is also High-K, calc-alkaline, and reflecting volcanic arc and post-collisional tectonic settings. Mineral chemical analyses show that the mafic minerals in the Vize pluton consist of Fe-biotite and calcic amphibole (hornblende). Ti-in biotite thermometry shows that the temperature of the pluton in the final crystallization temperatures are between 834 and 850 °C (mean = 845 ± 4 °C), while the crystallization temperatures of amphiboles are between 876 and 910 °C (mean = 893 ± 22 °C). Crystallization depths are estimated to be a range of 6.5 to 7.9 km. It can be assumed that the oxygen fugacity of calcic amphiboles (logƒO₂) is stabilized between −10.7 and − 11.3 bar (mean = −11.05 ± 0.4 bar). ∆NNO values are between 0.72 and 1.11 (mean = 0.96 ± 0.12) and H₂O melt content is between 4.63 % and 5.43 % (mean = 5.04 ± 0.4 %). Oxygen fugacity values are among the typical values of calc-alkaline magma crystallization.

The Vize pluton was crystallized in Cambrian to Ordovician times according to zircon UPb dating is concentrated in two different populations as 526.16 ± 3.26 Ma and 452.93 ± 2.76 Ma. All data obtained are consistent with the ages of the magmatism that produced the Vize Pluton in the Balkanides and Istranca Massif of 420–470 Ma (mean 447.17 ± 3.24 Ma) and indicate that it probably formed in the northern Gondwana. It was affected by the magma-mixing processes of coeval felsic and mafic magmas, and anatexis processes. Geochronological and geochemical data indicate the existence of a protracted magmatic activity related to convergent setting (long-lived magmatic arc) that forced the Vize-Pluton to undergo multi-stage melting-crystallization processes.