Forensic zirconology: tracing the magmatic and metallogenic evolution of intrusive porphyries of the Macquarie Arc, NSW, Australia


Research output: Chapter in Book/Conference paperConference paper


We report the results of a 'forensic zirconology' investigation into intrusives of the Ordovician-Silurian Macquarie Arc, southeastern Australia. This involves the sequential microanalysis of U-Pb, oxygen and hafnium isotopes, and trace elements contents, to fingerprint the source inputs and to deduce the crystallisation pathways and intensive parameters (T, oxygen fugacity) of the magmas. We aim to constrain the origin of the porphyry magmas and to explore the link between the nature and proportions of crustal and mantle sources and metal endowment. New geochronobgical data refines the magmatic history of the arc, particularly regarding the timing of medium-K magmatism and in identifying a Cambro-Ordovician component. Diversity in rare earth patterns implies a range of magmatic oxygen fugacity, and that the medium-K porphyries were intrinsically more oxidised than high-K to shoshonitic rocks. Temporat Hf-O isotope trends reveal that the oldest intrusives had depleted mantle-like Hf-176/Hf-177 but sub-mantle delta O-18, indicating a distinctive source component, whereas younger porphyries show a decrease in epsilon(Hf) accompanied by a rise in delta O-18, consistent with the progressive addition of supracrustal material. We interpret this trend to reflect evolution in tectonic setting, and suggest that the metallogenic fertility of the Macquarie Arc intrusives is influenced by a supracrustal contribution.

Original languageEnglish
Title of host publicationLET'S TALK ORE DEPOSITS, VOLS I AND II
EditorsF Barra, M Reich, E Campos, F Tornos
Number of pages3
ISBN (Print)978-956-287-329-1
Publication statusPublished - 2011
Event11th SGA Biennial Meeting on Let's Talk Ore Deposits - Antofagasta, Chile
Duration: 26 Sep 201129 Sep 2011


Conference11th SGA Biennial Meeting on Let's Talk Ore Deposits

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