SAPPHIRINE-QUARTZ AND SAPPHIRINE-CORUNDUM ASSEMBLAGES IN METAMORPHIC ROCKS ASSOCIATED WITH THE SEMAIL OPHIOLITE (UNITED-ARAB-EMIRATES)

Granulite facies metasedimentary and metavolcanic rocks occur imbricat ed with the Cretaceous Semail Ophiolite in the United Arab Emirates an d Oman. Peak metamorphic assemblages in highly oxidized lithologies of these rocks include sapphirine (7 : 9 : 3)-hercynitic etite-ilmeno-he matite-plagioclase-enstatite-quartz and sapphirine (2 : 2 : )-corundum -ilmeno-hematite-phlogopite-plagioclase. The observed mineral assembla ges in quartzitic rocks are an example of overlapping stability of sap phirine-quartz and spinel-quartz and are therefore not diagnostic for high pressures. Both types of sapphirine occur within the stability fi eld of Mg-rich cordierite. The common association of sapphirine and sp inel with magnetite and ilmeno-hematite in quartzitic rocks suggests t hat sapphirine was formed by a reaction including spinel, hematite and quartz on the educt side. Metamorphic conditions estimated from assoc iated parageneses point to temperatures of 800-850-degrees-C and press ures of 6.5-9 kbar.