The Menderes Massif, a 40000 km² exposure of polymetamorphic rocks in western Turkey, is a complex product of compression followed by extension, and a graben system continues to deform the massif today. Numerous studies report ages that 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 monazite ages are rarely consistent with a single population, and inclusions in garnet are typically older than matrix grains. For example, 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 (26.9±0.6 Ma) to Eocene (52.9±5.7 Ma). 

A 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. The growth-zoned 01-26 garnet, seen here to the left, has a higher Ca core, consistent with decompression, whereas a polymetamorphic history is recorded by southern massif 01-131 garnets, which show sharp increases in Mn and Mg, and decrease in Ca within their rims.  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.