P-T-t evolution of a large, long-lived, ultrahigh-temperature Grenvillian belt in central Australia

Abstract

The ~120,000 km2 Musgrave Province forms part of a continuous Musgrave-Albany-Fraser mid-late Mesoproterozoic orogenic system that transects central and southern Australia, and continues into formerly contiguous Antarctica. Voluminous felsic magmatic rocks that intruded over the interval 1330-1150 Ma, corresponding globally to the Grenvillian timeline, dominate the Musgrave Province. However, rare but widely distributed metapelitic granulites contain peakmetamorphic mineral assemblages comprising garnet + sillimanite ± quartz ± spinel. These are variably overprinted by coronae and/or symplectites of cordierite-bearing assemblages such as cordierite + spinel + magnetite ± plagioclase ± garnet. Petrologic forward modelling and Zr-in-rutile thermometry indicates these peak mineral assemblages developed at thermally extreme conditions of approximately 1000 °C and ca. 7-8 kbar. These ultra-high temperature (UHT) conditions appear to have prevailed throughout the Musgrave Province, across an approximate 600 kmstrike distance. The retrograde P-T evolution was characterised bymodest decreases in pressure during the initial high temperature segment of the cooling path, suggesting that the crust was not significantly thickened as a result of tectonism. Combined SIMS(SHRIMP) and LA-ICP-MS U-Pb geochronology constrains the total range of metamorphicmonazite growth/recrystallisation ages span 1263-1111 Ma with most individual samples spanning an age range of =80 Myr. The total age span implies approximately 150 Myr of perturbed thermal conditions during the Musgrave Orogeny. Our data requires thatmonazite is extremely resistive to isotopic resetting, evenwhen exposed to extreme thermal conditions for long (=80 Myr) periods. The thermal conditions, large regional footprint and long timescale of metamorphism and magmatism classify the Musgrave Province as a large, hot orogen.