U-Pb zircon geochronology and petrology of the early Miocene Goloba and Saroluk 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 postcollisional plutons are extensively seen. Two plutons in this peninsula were studied; the Goloba Pluton is composed of quartz monzonite, granite and granodiorite, and the Saroluk Pluton is composed of quartz monzonite, monzonite and granodiorite. U-Pb zircon dating yielded 20.87 +/- 0.31 Ma for the GOloba 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 Saroluk 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 GOloba and Saroluk 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 (La-N/Lu-N = 11-34), and slight negative Eu anomalies (Eu N /Eu* = 0.51-1.03). In the GOloba pluton samples, Sr-87/Sr-86((i)), Nd-143/ Nd-144((i)) and epsilon Nd(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 Saroluk pluton samples, Sr-87/Sr-86((i)) and Nd-143/Nd-144((i)) isotopic values range within 0.706978-0.707669 and 0.512456-0.512520 respectively, and epsilon Nd(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.