Subduction petrofabrics of lawsonite eclogite and blueschist facies rocks, Sivrihisar massif, Turkey

The Sivrihisar Massif, west-central Turkey, is an exhumed subduction complex consisting of metasedimentary and metabasaltic rocks that record lawsonite blueschist and eclogite facies conditions of metamorphism and deformation. Layers of marble, quartzite, calc-schist, and blueschist contain m-scale pods of lawsonite eclogite in the NW part of the massif. All rock types preserve textures and/or mineral assemblages that provide clues to metamorphic and deformation conditions at P > 2 GPa. To the SE, lawsonite has been replaced by epidote in metabasalt, indicating higher T conditions of metamorphism; EBSD analyses of quartz in quartzite and calcite in marble also show a progressive overprinting of HP microstructures. In the region most affected by overprinting, a progressive recrystallization front is observed in a change in calcite texture in marble, a change in white mica composition in quartzite, and transformation of eclogite and blueschist to greenschist and amphibolite. In this region, HP marble is characterized by rod-shaped calcite with long axes parallel to each other and oblique to foliation; most rods have a high angle to the foliation plane but some are sub-horizontal. Calcite rods are pseudomorphs after aragonite and have a strong CPO with the c-axis close to the long axis of the rods, irrespective of the orientation of the rod long axis relative to foliation. A narrow zone of partial recrystallization exists where the calcite rods are partially replaced by chains of small equant grains that maintain the CPO of the rods. This is succeeded by a narrow zone of recrystallized, equant calcite: rods are absent but CPO remains. At higher T (amphibolite facies), calcite grains are large and equant and have no CPO. In the lawsonite eclogite-bearing unit, quartzite is characterized by a single girdle c-axis fabric with some asymmetry, and some samples show a prism <a> point maximum. All show top-to-E (NE) shear sense, which is consistent with kinematic criteria in the interlayered marble. Further east, along a traverse in epidote blueschist-facies rocks, quartz c-axis patterns have cross-girdle patterns that show plane strain or constriction. Quartzite exhibits ubiquitous constrictional fabric in the region that has been overprinted by the lower-P, higher-T (Barrovian) metamorphism. Vorticity analyses conducted on the lawsonsite in both the eclogite pods and the blueschist layers shows simple shear dominating in the eclogite pods and pure shear in the blueschist layers. The obliquity of the calcite rods and the asymmetric quartz single girdles also suggest simple shear, whereas the cross girdles and constrictional girdles in some of the quartz suggest pure shear. The results of the microfabric analyses suggest that simple shear dominates deformation under HP conditions and that during ascent, HP rocks record more coaxial and constrictional flow that we assign in this case to transtension-accommodated exhumation.