U-Pb ages and Hf isotopic compositions of zircon from the Early Miocene Kestanbol Magmatic Complex in NW Anatolia (Turkey): Implications for crustal contribution in the post-collisional magmatism

摘要

The Tertiary post-collisional magmatic activity in NW Anatolia occurred after the Late Cretaceous to Early Tertiary collision of the Sakarya and Anatolide-Tauride blocks and the closure of the Izmir-Ankara Ocean. The magmatism resulted in coeval emplacement of granitic plutons and andesitic volcanic rocks along the IzmirAnkara-Erzincan Suture Zone (IAESZ). The Kestanbol Magmatic Complex (KMC) on the Biga Peninsula (W of the IAESZ), is one of the representative magmatic complexes in the Sakarya Zone situated north of the IAESZ. Monzo-dioritic (syeno-diorite) plutonic rocks show close relationships with dacitic, trachyandesitic and rhyolitic rocks in space and time which are characterized by enrichment in large-ion lithophile elements (LILE) and depletion in Nb, Ta, P and Ti, interpreted as reflecting an arc-related origin.Trace element concentrations and isotope data indicate that the KMC (the Kestanbol pluton, and the Ayvacik and the Balabanli volcanic rocks) was formed by differentiation of mantle-derived mafic melts via assimilation of ancient continental materials coupled with mineral fractionation. The zircon ages for the Kestanbol pluton and the Ayvacik volcanic rocks are 22.24 and 21.58 Ma, respectively, whereas zircon U-Pb age data suggest that the Balabanh volcanic rocks (19.33 +/- 0.30 Ma) is similar to 3 million years younger than the Kestanbol pluton and the Ayvacik volcanic rocks. I-If isotopes in zircon (epsilon Hf-(t) ranging from - 5.7 to -0.7), combined with U-Pb ages, support the hypothesis that the mantle source of the Kestanbol magmatism was severely modified by crust-derived metasomatic fluids during the previous subduction.