Thermal gradient and timing of high-T-low-P metamorphism in the Wongwibinda Metamorphic Complex, southern New England Orogen, Australia

S. J. Craven, N. R. Daczko*, J. A. Halpin

*Corresponding author for this work

    Research output: Contribution to journalArticle

    35 Citations (Scopus)

    Abstract

    The Wongwibinda Metamorphic Complex (WMC) is a high-temperature, low-pressure (HTLP) belt in the southern New England Orogen. It is characterized by a high metamorphic field gradient exposed in variably metamorphosed siliceous turbidites. The Abroi Granodiorite and the Rockvale and Tobermory adamellites, S-type granitoids of the Hillgrove Plutonic Suite, intrude the metaturbidites. Six samples of metaturbidite were studied from an ~3km long field traverse. Integrated petrography, mineral chemistry, and mineral equilibria modelling indicate a peak metamorphic temperature of 350-450°C in the lowest grade rocks and ~660°C in the highest-grade rocks. Maximum pressure does not exceed 3.5kbar anywhere, implying a maximum depth of 12km and indicating an average vertical gradient of at least 55°Ckm -1, though our calculations suggest this is not linear. Metamorphic isograds show no apparent relationship with distance to the exposed margins of the Hillgrove Suite granitoids. Electron microprobe U-Th-Pb monazite data indicate a date of 296.8±1.5Ma for the thermal peak of the HTLP metamorphism. Laser ablation inductively coupled plasma mass spectrometry indicates a zircon U-Pb crystallization age of 290.5±1.6Ma for the Abroi Granodiorite, confirming that the pluton post-dates the peak HTLP metamorphism. Consequently, magmatic advective heat transfer from depth via emplacement of a large volume of granitoid is unlikely to be the key local driver of the high-grade metamorphism. It is concluded that published evidence of an extensional geodynamic setting around the Carboniferous-Permian boundary supports conductive heat transfer as the key driver of HTLP metamorphism for the WMC. It is not possible to exclude magmatic advective heat transfer via emplacement of mantle derived basaltic magmas in the deeper crust.

    Original languageEnglish
    Pages (from-to)3-20
    Number of pages18
    JournalJournal of Metamorphic Geology
    Volume30
    Issue number1
    DOIs
    Publication statusPublished - Jan 2012

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