Integrating lawsonite bearing eclogite and blueschist into the structural evolution of the Sivrihisar massif

Lawsonite eclogite and blueschist-facies rocks occur in contact with metasedimentary host rocks in the Sivrihisar massif, part of the Tavsanli Zone of western Turkey, provide new context to the Neo-Tethyan subduction and exhumation processes that occurred prior to and exhumation that occured during the Cretaceous Anatolide continental collision and basin closure. The Sivrihisar massif is comprised of four WNW-ESE striking belts dominated by metasedimentary schist and marble with lesser amounts of metabasalt that have a bulk composition equivalent to NMORB. Metabasalts in three of the four belts record decreasing maximum pressure conditions (P-max) from ~ 26 kbar from lawsonite eclogite and ~ 18 kbar from epidote eclogite in the northern most Halilbagi belt, 15-16 kbar from lawsonite-epidote blueschist in the central Karacaoren belt, and 8-12 kbar from incipient blueschist facies on epidote + chlorite greenschist facies metabasalt in the Kertek belt to the south. Most rocks contain a pervasive foliation, (S1) parallel to compositional layering (S0), and mineral lineations (stretched and/or aligned) composed of minerals such as quartz, omphacite, sodic-amphibole, lawsonite, pressure shadows on garnet and lawsonite. Inclusions trails in garnet and lawsonite suggest that S0/S1 is a composite fabric that records pre- to post P-max in the Halilbagi and Karacaoren belts. S0/S1 predates incipient blueschist in the Kertek belt. Folds (F2) of S0/S1 are typically asymmetric and tight to isoclinal. F2 folds are south-vergent and moderately easterly plunging in the Halilbagi and northern portion of the Karacaoren belts. F2 axes become more horizontal from north to south across the Karacaoren belt. F2’s are recumbent in the Kertek belt. F3 folds are consistently upright open to closed with NNW plunging axes across the massif. Fibrous calcite, interpreted to be pseudomorph after aragonite, occurs parallel to F3 fold axes across the massif. Shear sense indicators from field observations and asymmetric type-I cross girdle of quartz c-axes obtained from electron backscatter diffraction (EBSD) show top to the south thrusting for much of the massif with the exception of the far northern margin. The Halilbagi belt was thrust onto the Karacaoren belt possibly below a depth of 45 km during extrusion along the subduction channel. Exhumation from this structural level may have coincided with the arrival of the Anatolide micro-continent into the subduction zone at approximately 70 Ma. The homogeneous orientation of calcite fibers and F3’s across the Massif suggests that assembly occurred at blueschist conditions before exhumation through the aragonite-calcite transition ~ 350 degrees C above 8 kbar.