HIGH-RESOLUTION GARNET P-T PATHS FOR THE CENTRAL MENDERES MASSIF, WESTERN TURKEY

Garnet-based thermobarometry is often used to develop models for the evolution of the central Menderes Massif, a large-scale metamorphic core complex in western Turkey. Menderes Massif P-T conditions constrain processes that worked to assemble western Turkey and link the massif to core complexes in the Aegean region. Here we report P-T conditions from greenschist- to amphibolite-facies garnet-bearing rocks collected along three transects across the Alasehir detachment, a structure responsible for the exhumation of the central portion the massif. High-resolution BSE images and X-ray Fe, Ca, Mg, Mn, and Y maps were collected from garnets and quantitative compositional data were obtained from garnet and matrix phases to estimate peak P-T conditions using classical thermobarometry. This data suggest that rocks experienced conditions from 575±25°C and 10±1 kbar to 715±55°C and 11.2±2.2 kbar. However, results from adjacent samples are inconsistent, potentially due to disequilibrium among phases and/or the application of barometers to inappropriate (uncalibrated) mineral compositions. Using an alternative G-minimization approach with bulk rock composition estimates and preserved mineral zoning, we obtained garnet core and rim P-T conditions, and high-resolution P-T paths. Garnet core P-T conditions range between 6-9 kbar and 530-630^oC and rim conditions range from 6.3-10 kbar and 625-750^oC. Most P-T paths show a continuous increase in temperature with pressure, suggesting growth during burial. One sample shows an increase in temperature, but pressure fluctuates from 9.3 kbar (core) to 8.9 kbar (mantle) to ~10 kbar (rim). Interestingly, the final pressure for this rock is 2-3 kbar higher than rocks near-by (<1 km), but thermal conditions are consistent. Th-Pb monazite ages for the samples range from 35.8±3.0 to 20.6±2.4 Ma, and with continuous heating recorded by garnet, suggest the suite of rocks was metamorphosed over a single, 15 m.y. period. Although additional garnet P-T paths are still needed, our findings capture garnet growth related to a single metamorphic event and define some of the most consistent and detailed P-T paths reported for the area. The results differ from recent findings in the southern Menderes Massif that indicate garnet-bearing rocks there record alternations in burial and exhumation.