Metamorphic history of the southern Menderes massif, western Turkey

Metamorphic mineral compositions and textures are integrated with microstructures to test tectonic models for the construction and exhumation of a mid-crustal terrane in western Turkey. The southern Menderes massif, part of the Alpine orogen, is composed of a tilted sequence of metasedimentary rocks that structurally overlies orthogneiss. Garnet-biotite equilibria for schists collected along north-south traverses consistently indicate temperatures of 430 °C for the southernmost, structurally highest garnet-bearing rocks, ~500 °C for structurally intermediate rocks, and ~550 °C for the structurally deepest rocks near the contact with the orthogneiss. There are no detectable discontinuities in metamorphic grade from north to south within the schist unit, or between the schist and overlying lower-grade and underlying higher-grade rocks. Pressure estimates are less certain; geobarometric results for the schists yield P ≈ 8 kbar, but mineral assemblages and structural data are consistent with lower pressures (≤6 kbar). Metamorphic textures and garnet zoning in the Menderes schists indicate metamorphism during a single thermal event accompanying development of the main penetrative foliation. Top-to-north fabrics formed during folding/thrusting and were synkinematic with garnet growth. Top-to-south chloritic shear bands truncate the earlier foliation and overprint peak-metamorphic assemblages and textures. We propose that these metamorphic features and structures indicate synmetamorphic shortening followed by extension during Alpine orogenesis.