Long-term exhumation of an Aegean metamorphic core complex granitoids in the Northern Menderes Massif, western Turkey

Abstract

The Egrigoz, Koyunoba, and Alacam plutons are located in the northern portion of the Menderes Massif, a region characterized today by large-scale extension. To gain a better understanding of their exhumation history, we acquired zircon ages, geochemical analyses, and cathodoluminescence (CL) images to search for evidence of micro- to macro-scales of deformation. The combination is a powerful means to decipher their tectonomagmatic history. In situ ion microprobe 238U/206Pb zircon ages of the granitoids range from 30.0 ± 3.9 Ma to 14.7 ± 2.6 Ma (±1σ) and indicate the plutons crystallized over ∼15 m.y. The dated zircons show CL zoning consistent with igneous crystallization and are only located adjacent to or as inclusions in biotite grains. The youngest ages are dominated by a blue color in CL, whereas a majority of older zircons are yellow. Higher Th/U contents are typically shown by zircons with black or dark green colors in CL. Most of the samples of these granitoids indicate they are magnesian, calc-alkalic and peraluminous granite to granodiorites, but variations exist, likely reflecting heterogeneity caused by magma mixing, partial melting, crustal contamination, and post-emplacement fluid interactions as evidenced by the CL images. CL images show that all samples experienced magma mixing, multiple episodes of brittle deformation, and fluid-mediated alteration. Sources for the generation of Northern Menderes Massif granitoids include simple slab induced upwelling from the subduction of the African plate along the Hellenic arc, adiabatic decompression as the northern edge of Turkey9s Anatolide-Tauride block delaminates, and upwelling asthenosphere as the continental lithosphere thins during extension. We present a model in which western Turkey is an amalgamation of stacked subduction zones that transition from north to south over time. Northern Menderes Massif granitoids document their complex geologic history in their ages, chemistry, and textures.