A NOVEL APPROACH FOR EXTRACTING EARLY, HIGHER-P RECORDS FROM ROCKS OVERPRINTED AT HP-LT CONDITIONS: INTEGRATING METAMORPHIC PETROLOGY AND MAGNETIC FABRICS OF AMPHIBOLITES EXHUMED IN A MIGMATITE DOME

In metamorphic rocks transformed along a clockwise P–T path, the difference between maximum pressure (P) and the P at peak temperature (T) may be substantial. Recovering the higher-P history is a challenge. Integrating results of thermobarometry and analysis of magnetic fabrics of refractory rocks in migmatite domes is a new method to recover some of the chemically-erased record of the higher-P history. In migmatite domes that formed by vertical flow of partially molten crust, deep rocks are transported to shallower crustal levels, experiencing a wide range of Ps at high-T. The Entia Dome, central Australia, is a well-exposed double migmatite dome formed during the Ordovician-Carboniferous Alice Springs Orogeny as a result of reworking of older, Proterozoic crust (e.g. Hand et al., 1999; Wade et al., 2008). The domal structure contains refractory mafic and aluminous lithologies that are more likely to preserve a substantial record of the P–T history of dome evolution than the dominant quartzofeldspathic gneiss that records only HT–LP conditions of dome emplacement. We are investigating the potential for mafic rocks (primarily amphibolites) to preserve a structural and metamorphic record of early, higher-P conditions in order to understand the origin and depths at which mafic protoliths are sourced before integration and deformation in the domal structure. Recent advances in characterizing Anisotropy of Magnetic Susceptibility (AMS) of single crystal amphiboles and models relating AMS and petrofabrics in amphibolites have opened new avenues for systematically studying the structural record of deformation preserved in amphibolites based on magnetic fabrics developed during high P–T metamorphic events (Biedermann et al., 2015, 2018). In this study, we integrate metamorphic records of P–T–X history preserved in hornblende + plagioclase ± clinopyroxene ± quartz ± garnet ± rutile ± titanite bearing amphibolites in the Entia Dome with low- and high-field measurements of AMS. We study the systematic relationships between mineral assemblages and compositions, mineral and magnetic fabrics, and 3D structural records of deformation related to doming preserved in these refractory lithologies in order to better characterize the full P–T–X–t–d record of dome formation and evolution in the Entia Dome.