The petrotectonic evolution of the Sivrihisar Massif, Turkey

High-pressure-low-temperature (HP-LT) metamorphic rocks such as blueschist and eclogite are interpreted to mark the location of ancient subduction zones. These rocks are typically interlayered with rocks that either did not experience, or did not record, HP-L T metamorphism. Understanding when HP-L T and non-HP-LT rocks were juxtaposed is important to unraveling the tectonic processes of subduction and exhumation. Coherent exposures that record these processes are rare due to petrologic and mechanical overprinting that occurs during exhumation. The Sivrihisar Massif of west-central Turkey contains well-preserved blueschist and eclogite facies rocks interlayered with metasedimentary rocks. Eclogite and blueschist from within the massif record decreasing maximum pressure (P-max) conditions, from lawsonite eclogite facies in the northernmost Halilbagˇi belt (25 kbar), to lawsonite blueschist facies in the central Karacaoren belt (14-16 kbar), to incipient blueschist facies in the Kertek belt to the south. Most rocks contain a pervasive foliation as well as aligned and elongated HP-LT minerals such as omphacite, sodic-amphibole and lawsonite. The first of two generations of folds (F2) change systematically across the field area, however F3 orientations are consistent across the massif. F2 and F3 development post-date P-max in the Halilbagˇi and Karacaoren belts, but F3 is syn-tectonic with incipient blueschist conditions in the Kertek belt. Shear sense indicators and quartz c-axis orientations obtained from electron backscatter diffraction (EBSD) show top to the south thrusting across the massif. Several of the hundreds of lens shaped pods within the Halilbagˇi belt contain interlayered and folded (F2) lawsonite eclogite and blueschist in the core. The margin of one pod is shown to have developed under eclogite conditions. The Halilbagˇi and Karacaoren belts may have been juxtaposed at a depth of 45 km, possibly during extrusion along the subduction channel. Exhumation from this structural level may have been assisted by the arrival of the Anatolide micro-continent into the subduction zone at approximately 70 Ma. The homogeneous orientation of calcite fibers (pseudomorph after aragonite) and F3's across the massif suggests that assembly of the massif occurred at blueschist conditions before exhumation through the aragonite-calcite transition at 350°C and >8 kbar.