Petrology and phase relations of the kyanite-eclogites from eastern Turkey

Abstract

Eclogites are found as lenses or layers in the Precambrian gneiss terrain of the Bitlis Massif in eastern Turkey. Kyanite-eclogites from the region of Gablor Hill in the Bitlis Massif exhibit relatively minor alteration, and consist of garnet, omphacite, kyanite, zoisite, calcic amphibole, phengite, rutile and quartz. In terms of geological setting and mineral compositions, Gablor eclogites are very similar to eclogites from high-grade gneiss terrains. Metamorphic conditions during the eclogite crystallisation are determined as 625±35° C and 16±3 kbars. The coexistence of white mixa, omphacite and kyanite constrains $$a_{{\text{H}}_{\text{2}} {\text{O}}} $$ between 0.4 and 1. Primary calcic amphiboles from the Gablor eclogites exhibit conflicting textures, indicating stable coexistence with, as well as growth from omphacite and garnet. This is explained by a buffering reaction between amphibole, garnet, omphacite, zoisite and kyanite during the eclogite crystallisation, whereby $$a_{{\text{H}}_{\text{2}} {\text{O}}} $$ is controlled and buffered by the mineral assemblage.