Tectonometamorphic evolution of the Southern and Central Menderes Massif, western Turkey

Geologic history of the Menderes Massif (MM), western Turkey is difficult to discern, partly due to a series of collisional and extensional events, each imparting a deformation fabric and, in some cases, producing recrystallization of prograde metamorphic minerals. To avoid recrystallization effects, we focused on garnet crystals, which commonly retain prograde chemical zoning, and constructed thermodynamic models of chemical zoning from cores to rims, yielding estimates of pressure (P) and temperature (T) changes during prograde growth.

Models from Selimiye nappe rocks in the Southern Menderes Massif (SMM) show an almost linear P-T path from 555-570^oC and 5.9-6.0 kbar to 582-586^oC and 7.3-7.7 kbar. Models from Çine nappe rocks in the SMM show "N-shaped" P-T paths where core growth initiates at 510-551^oC and 5.1-5.9 kbar and rim growth terminates at 568-583^oC and 6.1-7.0 kbar, with observed mid-path P decreases of up to 1.0 kbar. In the Central Menderes Massif (CMM), in Bozdağ and Bayındır nappe rocks, only two paths were successfully modeled (from adjacent outcrops in the same structural block in the Bayındır nappe). The first starts at 565^oC and 6.4 kbar and increases to 592^oC and 7.5 kbar, and the second is isobaric from 531^oC and 7.1 kbar to 571^oC and 7.3 kbar. Additional P-T estimates of garnet core growth in the CMM rocks, applied to highest spessartine concentrations near garnet geometric centers and made by isopleth thermobarometry, give 530-625^oC and 6.0-7.0 kbar.

If intracrystalline diffusion affected CMM core chemical zoning, growth conditions may be overestimated. Further, given the inconsistency between Bayındır paths, we propose CMM garnets experienced thermal conditions different from CSM samples. The simple SMM paths suggest Selimiye nappe garnets grew during continuous burial whereas complex Çine nappe paths are consistent with repeated burial. Overlap between the Selimiye path and the second Çine pressure increase may imply contemporaneous growth during a second burial event, possibly from overthrusting of Cyclades-Menderes Thrust hanging wall following closure of the Izmir-Ankara Ocean during the Alpine Orogeny.