Implications for Thrust‐Related Shortening Punctuated by Extension From P‐T Paths and Geochronology of Garnet‐Bearing Schists, Southern (Çine) Menderes Massif, SW Turkey

Abstract

AbstractThe Menderes Massif, Turkey, is a type locality for deciphering the plate tectonic response from collision‐ to extension‐driven exhumation. Conventional thermobarometry and garnet pressure‐temperature (P‐T) paths from isochemical phase diagrams were calculated across a major fault (Selimiye Shear Zone, SSZ) bounding the southern edge of the Menderes Massif. Both approaches yield similar garnet rim temperatures (from 555 to 671 °C), but estimated P differs by between 8 and 15 kbar. Three garnets north of the SSZ reveal N‐shaped P‐T paths, whereas paths from three samples south of the SSZ show a simple increase in P‐T. Monazite and zircon were dated in thin section from the same rocks using Secondary Ion Mass Spectrometry and Laser Ablation Inductively Coupled Plasma‐Mass Spectrometry, respectively. Textural relationships of monazite within garnet appears indicative of post‐garnet growth. The amount of monazite common 204Pb and 137Ba+/Th+ significantly exceeds what is observed for the monazite age standard, suggesting their ages mark fluid‐driven events, loosely constrained to Late Eocene‐Early Miocene. Some zircon ages are consistent with Cambro‐Ordovician ages reported elsewhere in the region, and other ages are Neoproterozoic and Permian‐Triassic, a period not previously recognized in this area. Despite the lack of age constraints for the duration of garnet growth, we present a thermal model to understand the meaning of the N‐shaped path. These paths are best reproduced by thermal models incorporating SSZ thrusting before and after denudation. This paper presents an example of the insight from high‐resolution P‐T paths, and an example of denudation within a prograde metamorphic event.