GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 229-4
Presentation Time: 2:20 PM


ETZEL, Thomas M.1, LIZZADRO-MCPHERSON, Daniel1, KELLY, Eric D.2, CATLOS, Elizabeth J.1, ASHLEY, Kyle T.1, OZERDEM, Cenk3 and CEMEN, Ibrahim4, (1)The Jackson School of Geosciences, The Unversity of Texas at Austin, 2275 Speedway Stop C9000, Austin, TX 78712, (2)The Jackson School of Geosciences, The Unversity of Texas at Austin, Austin, TX 78712, (3)Boone Pickens School of Geology, Oklahoma State University, Stillwater, OK 74078, (4)Department of Geological Sciences, University of Alabama, Tuscaloosa, AL 35406,

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 530-630oC and rim conditions range from 6.3-10 kbar and 625-750oC. 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.