High Water Activities in the Generation of High Pressure Kyanite Eclogites of the Tauern Window, Austria

Quartz-kyanite eclogites in the Tauern Window of the Eastern Alps contain abundant hydrous phases and carbonates. Glaucophane-kyanite eclogites have been identified, and the relationships among the phases paragonite, glaucophane, zoisite, talc, magnesite and dolomite in association with garnet, omphacite, kyanite and quartz are discussed. Quartz-omphacite-kyanite veins, together with the observation of aqueous fluid inclusions ({aastex} {amsbsy} {amsfonts} {amssymb} {bm} {mathrsfs} {pifont} {stmaryrd} {textcomp} {portland,xspace} {amsmath,amsxtra} {wasysym} {empty} {10}{9}{7}{6} {document}X_CO₂ < 0.1,\ XNaCl ≤ 0.02{document}) in omphacite and zoisite suggest crystallisation under conditions of high water activity. Conditions of {aastex} {amsbsy} {amsfonts} {amssymb} {bm} {mathrsfs} {pifont} {stmaryrd} {textcomp} {portland,xspace} {amsmath,amsxtra} {wasysym} {empty} {10}{9}{7}{6} {document}620 ± 30∘C,\ 19.5 ± 2.5\ kb,\ X_CO₂ = 0.02 ± 0.02{document}, are indicated by the coexistence of the assemblages paragonite + omphacite + kyanite and dolomite + omphacite + quartz. Two structural subareas within the Peripheral Schieferhülle of the Pennine domain have been identified in the Grossven-ediger area; one subarea comprises metabasites which underwent eclogite facies conditions along with their enclosing metasediments. It was tectonically introduced into the rest of the Schieferhiille prior to the development of blueschist facies assemblages and the overthrusting of the Austroalpine nappes. The process of subduction is required to explain the depths (ࣈ 70 km) implied by the mineral assemblages developed.