REMOTELY SENSED IMAGES, ZIRCON AGES, CATHODOLUMINESCENCE, AND GEOCHEMISTRY OF NORTHERN MENDERES MASSIF GRANITOIDS: EVIDENCE FOR LONG-TERM EXHUMATION OF AN AEGEAN METAMORPHIC CORE COMPLEX

The Eğrigöz, Koyunoba, and Alaçam plutons are located in the Northern Menderes Massif of western Turkey between the Simav normal fault to the south and the Izmir-Ankara-Erzincan suture to the north. Although much attention has focused on their geochemical and geochronological history, their relationship to each other and other major structures in the region is debated. Some geologic maps show Eğrigöz and Koyunoba pluton bounded to the west and separated from the Alaçam body by the low-angle Simav detachment fault. In contrast, other regional maps show no offsets. To gain a better understanding of the exhumation history of the plutons, remotely-sensed images, geochronological data, geochemical analyses, and cathodoluminescence (CL) images were acquired to search for evidence of micro- to macro-scales of deformation. Numerous ~E-W trending extension lineations parallel the Simav normal fault and cut the plutons. These lineations are due to large-scale ~N-S extension that continues after their exhumation. In situ ion microprobe ²³⁸U/²⁰⁶Pb zircon ages of the granites range from 29.9±3.9 Ma to 14.6±2.6 Ma (±1s) and suggest the plutons crystallized over ~15 m.y. The dated zircons are located adjacent to or as inclusions in biotite, a relationship related to the crystallization history of the rocks. The majority of the reported compositions of these granites indicate they are magnesian, calc-alkalic and peraluminous granite to granodiorites. Geochemical analyses show little difference between the three plutons, consistent with the rocks arising from a similar source, likely a post-collisional volcanic-arc. CL images show that all samples experienced magma mixing, multiple episodes of brittle deformation, and fluid-mediated alteration. Instead of a single easily identifiable detachment working to exhume these granites, our results are consistent with a model where they exhumed via large-scale extension along multiple discrete normal faults.