Geochemical and mantle-like isotopic (Nd, Sr) composition of the Baklan Granite from the Muratdagi Region (Banaz, Usak), western Turkey: Implications for input of juvenile magmas in the source domains of western Anatolia Eocene-Miocene granites

摘要

The (late syn)- post-collisional magmatic activities of western and northwestern Anatolia are characterized by intrusion of a great number of granitoids. Amongst them, Baklan Granite, located in the southern part of the Muratdagi Region from the Menderes Massif (Banaz, Usak), has peculiar chemical and isotopic characteristics. The Baklan rocks are made up by K-feldspar, plagioclase, quartz, bio-tite and hornblende, with accessory apatite, titanite and magnetite, and include mafic microgranular enclaves (MME). Chemically, the Baklan intrusion is of sub-alkaline character, belongs to the high-K, calc-alkaline series and displays features of I-type affinity. It is typically metaluminous to mildly peraluminous, and classified predominantly as granodiorite in composition. The spider and REE patterns show that the rocks are fractionated and have small negative Eu anomalies (Eu/Eu~* = 0.62-0.86), with the depletion of Nb, Ti, P and, to a lesser extent, Ba and Sr. The pluton was dated by the K-Ar method on the whole-rock, yielded ages between 17.8 ±0.7 and 19.4 ± 0.9 Ma (Early Miocene). The intrusion possesses primitive low initial ~(87)Sr/~(86)Sr ratios (0.70331-0.70452) and negative ε((Nd(t))) values (-5.0 to -5.6). The chemical contrast between evolved Baklan rocks (SiO_2) 62-71 wt.%; Cr, 7-27 ppm; Ni, 5-11 ppm; Mg#, 45-51) and more primitive clinopyroxene-bearing monzonitic enclaves (SiO_2, 54-59 wt.%; Cr, 20-310 ppm; Ni, 10-70 ppm; Mg#, 50-61) signifies that there is no co-genetic link between host granite and enclaves. The chemical and isotopic characteristics of the Baklan intrusion argue for an important role of a juvenile component, such as underplated mantle-derived basalt, in the generation of the granitoids. Crustal contamination has not contributed significantly to their origin. However, with respect to those of the Baklan intrusion, the generation of the (late syn)- post-collisional intrusions with higher Nd(t) values from the western Anatolia require a much higher amount of juvenil component in their source domains.