IN SITU TIMING CONSTRAINTS FROM THE MENDERES MASSIF, WESTERN TURKEY

The Aegean extended terrane of southeastern Europe contains the Cycladic and its eastern continuation, the Menderes Massif, in western Turkey. Although the metamorphic core complex origin of the Menderes Massif is well accepted, its metamorphic history has remained relatively unstudied. The massif exposes a 60000 km² area of polymetamorphic rocks, which were subjected to compression followed by extension, and a graben system continues to deform the massif today. Numerous reported ages support a polyphase deformation history of the massif, but their link to the nature of specific events remains difficult and controversial. Problematic aspects include distinguishing Pan-African deformation from Alpine tectono-metamorphic evolution, and discriminating Eocene/Oligocene compression from recent extension. To decipher the chronology, monazite in garnet-bearing rocks from Menderes Massif’s northern, central, and southern sections were dated in situ using the Th-Pb ion microprobe method. Menderes Massif garnets were also element mapped as garnets commonly show zoning that reflects growth events or diffusional modification, providing information about the integrated thermal history of the sample. Menderes monazite ages are rarely consistent with a single population, and inclusions in garnet are typically older than matrix grains. For example, a northern rock 59-19/124b has three monazite inclusions in garnet that average 37.9±0.9 Ma (1s), whereas a matrix grain is 32.8±0.5 Ma. Matrix monazites in northern sample 30 are Miocene to Eocene. A growth-zoned garnet in northern rock 01-26 has a 36.0±0.6 Ma inclusion, but matrix monazites range from 28.2±0.4 Ma to 41.4±1.3 Ma. Matrix zircons from northern massif sample 01-13 are Pan African (²⁰⁷Pb/²⁰⁸Pb 508±92 Ma). More recent deformation events failed to erase all traces of this pre-Alpine evolution, as Pan African monazites in garnet are found in central sample 01-88 (498±8 Ma) and southern sample 01-141 (499±18 Ma). Garnets in 01-88 are diffusionally homogenized, and 01-88 matrix monazites in reaction with allanite yield 17±5 Ma and 4.5±1.0 Ma. As 01-88 was collected along a detachment surface, the monazite ages suggests the structure actively exhumed rocks from deep crustal depths (minimum 400°C) since the Pliocene.