The geochemical and Sr-Nd isotopic characteristics of Eocene to Miocene NW Anatolian granitoids: Implications for magma evolution in a post-collisional setting

摘要

Early Eocene to Early Miocene magmatic activity in northwestern Anatolia led to the emplacement of a number of granitoid plutons with convergent margin geochemical signatures. Granitoid plutons in the area are mainly distributed within and north of the suture zone formed after the collision of the Anato-lide-Tauride platform with the Pontide belt. We present geochemical characteristics of three intrusive bodies in the region in order to identify their source characteristics and geodynamic significance. Among these, the Cataldag and Ilica-Samli plutons are located to the north and the Orhaneli pluton is located to the south of the IAESZ (Izmir-Ankara-Erzincan Suture Zone). The plutons are calc-alkaline, metaluminous, and Ⅰ-type with compositions from granite to monzonite. They display clear enrichments in LILE and LREE and depletions in HFSE relative to N-MORB compositions and have high ~(87)Sr/~(86)Sr and low ~(143)Nd/~(144)Nd ratios. The results of theoretical Fractional Crystallization (FC) model show that the samples are affected by fractionation of K-feldspar, plagioclase, biotite and amphibole. Assimilation and Fractional Crystallization (AFC) modeling indicates that the r value, the proportion of variable contamination to fraction, is high, . indicating significant crustal contamination in the genesis of granitoid magmas. Combined evaluation of isotopic and trace element data indicates that the granitoids are the products of mantle-derived mafic magmas variably differentiated by simultaneous crustal contamination and fractional crystallization in lower to middle crustal magma chambers in a post-collisional setting.