Lawsonite eclogite pods ranging in size from 3 cm to 6 m occur in lawsonite blueschist and eclogite facies metasedimentary and metabasaltic rocks in the Sivrihisar Massif, Turkey. Some pods have a core of lawsonite eclogite surrounded by alternating, centimeter-scale layers of lawsonite blueschist, eclogite, and transitional eclogite-blueschist, all with similar basaltic bulk composition. These pods also contain texturally late lawsonite-rich veins and layers. Most eclogites and blueschists within the pods lack reaction textures, but some blueschists near pod margins contain texturally complex garnet as well as glaucophane rims on omphacite, suggesting retrogression of eclogite to blueschist. Phase diagrams (pseudosections) calculated for the lawsonite eclogite core of a meter-scale pod indicate that the eclogite equilibrated at ∼22-24 kbar, ∼520°C. Lawsonite eclogite and blueschist at the tectonized margin of the same pod equilibrated at similar temperatures and slightly lower pressures. The composite eclogite-blueschist pod is foliated, lineated, and folded. An earlier generation of lineated omphacite in the pod core has a different spatial orientation than the lineation at the pod margin, although electron backscattered diffraction data show that core and rim omphacite have similar lattice preferred orientation patterns. Petrologic and structural data are consistent with mechanical formation of pods by folding and dissection of eclogite layers at high-P, and localized retrogression at pod margins during initial stages of exhumation at P-T conditions >425°C, 16 kbar.
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Acknowledgments This work was partially supported by NSF grant EAR-0711263 to D. Whitney and graduate student research funds from the Department of Geology & Geophysics at the University of Minnesota to P. Davis. We thank S. Wallis and H. Marschall for their helpful reviews, as well as A. Okay for interesting discussions. Field assistance was provided by M. Aydın Ayc¸enk, Osman Kendir, and Tamer Koralay.
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