U–Pb zircon geochronology and petrology of the early Miocene Göloba and Şaroluk plutons in the Biga Peninsula, NW Turkey: Implications for post-collisional magmatism and geodynamic evolution

Abstract

The Biga Peninsula (NW Turkey) is an area where magmatic and tectonic events are observed together, and post-collisional plutons are extensively seen. Two plutons in this peninsula were studied; the Göloba Pluton is composed of quartz monzonite, granite and granodiorite, and the Şaroluk Pluton is composed of quartz monzonite, monzonite and granodiorite. U–Pb zircon dating yielded 20.87 ± 0.31 Ma for the Göloba pluton, 19.69 ± 0.25 Ma for a quartzmonzonite porphyry vein cutting this pluton, and 22.18 ± 0.40 to 21.51 ± 0.37 Ma for the Şaroluk pluton, revealing an Early Miocene emplacement age for these pluton magmatism. These plutons are geochemically similar to each other with high-K calc-alkaline compositions. Their A/CNK values range between 0.84 and 1.48, suggesting I-type and metaluminous to slightly peraluminous characteristics. The rock samples show linear-like correlations in major oxide and trace element variation diagrams, which indicate main mineral phase’ fractionation. The Göloba and Şaroluk plutons also exhibit enrichment in large ion lithophile elements (K, Sr, Rb and Ba), Ce and Th, with decreases in high field strength elements (Ti and Y), Ta and Nb. Chondrite normalised REE diagrams of the plutonic rocks show concave upward patterns (LaN/LuN = 11–34), and slight negative Eu anomalies (EuN/Eu* = 0.51–1.03). In the Göloba pluton samples, 87Sr/86Sr(i), 143Nd/144Nd(i) and ƐNd(i) values vary from 0.706792 to 0.707250, from 0.512435 to 0.512489, and from −2.36 to −3.41, respectively. In the Şaroluk pluton samples, 87Sr/86Sr(i) and 143Nd/144Nd(i) isotopic values range within 0.706978–0.707669 and 0.512456–0.512520 respectively, and ƐNd(i) values are between −1.75 and −2.99. Fractional crystallisation, rather than assimilation and mixing, seems to have been important in the evolution of the studied plutons. All geochemical data suggest that the parental magma(s) of the studied plutons were hybrid magma that originated from enriched lithospheric mantle and lower/middle crust end-members. According to the regional geology and petrological data, Neogene magmatism in the Biga Peninsula has post-collisional feature, and was closely related to slab break-off.