Eclogitisation of gabbroic rocks: Redistribution of trace elements and Zr in rutile thermometry in an Eo-Alpine subduction zone (Eastern Alps)

The trace element characteristics of accessory minerals in eclogites help to reconstruct the P-T-t evolution of a subduction complex: U-Pb zircon ages will date the high-pressure event if U-Th characteristics and REE analyses constrain zircon growth to being metamorphic and essentially synchronous with the growth of garnet. Recent studies document that variations in Zr content of rutile grown in the presence of zircon and quartz are mainly attributable to differences in temperature. Zr-in-rutile thermometry of Koralpe, Saualpe and Pohorje eclogites yields temperatures of 700-730 °C (according to Zack et al. [Zack, T., Moraes, R., Kronz, A., 2004. Temperature dependence of Zr in rutile: an empirical calibration of a rutile thermometer. Contrib. Mineral. Petrol. 148, 471-488]) or between 630-650 °C (according to Watson et al. [Watson, E.B., Wark, D.A., Thomas, J.B., 2006. Crystallization thermometers for zircon and rutile. Contrib. Mineral. Petrol. 151, 413-433]). No systematic variation in rutile temperatures was observed for matrix rutile and rutile included in garnet, omphacite or kyanite, suggesting that these temperatures represent peak metamorphic conditions and that this part of the Austroalpine basement behaved as a coherent block during subduction.