Major zircon megacryst suites of the Indo-Pacific lithospheric margin (ZIP) and their petrogenetic and regional implications

Lin Sutherland, Ian Graham, Gregory Yaxley, Richard Armstrong, Gaston Giuliani, Paul Hoskin, Victor Nechaev, Jon Woodhead

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Zircon megacrysts (± gem corundum) appear in basalt fields of Indo-Pacific origin over a 12,000 km zone (ZIP) along West Pacific continental margins. Age-dating, trace element, oxygen and hafnium isotope studies on representative zircons (East Australia–Asia) indicate diverse magmatic sources. The U–Pb (249 to 1 Ma) and zircon fission track (ZFT) ages (65 to 1 Ma) suggest thermal annealing during later basalt transport, with < 1 to 203 Ma gaps between the U–Pb and ZFT ages. Magmatic growth zonation and Zr/Hf ratios (0.01–0.02) suggest alkaline magmatic sources, while Ti—in—zircon thermometry suggests that most zircons crystallized within ranges between 550 and 830 °C. Chondrite-normalised multi-element plots show variable enrichment patterns, mostly without marked Eu depletion, indicating little plagioclase fractionation in source melts. Key elements and ratios matched against zircons from magmatic rocks suggest a range of ultramafic to felsic source melts. Zircon O-isotope ratios (δ18O in the range 4 to 11‰) and initial Hf isotope ratios (εHf in the range +2 to +14) encompass ranges for both mantle and crustal melts. Calculated Depleted Mantle (TDM 0.03–0.56 Ga) and Crustal Residence (0.20–1.02 Ga) model ages suggest several mantle events, continental break-ups (Rodinia and Gondwana) and convergent margin collisions left imprints in the zircon source melts. East Australian ZIP sites reflect prolonged intraplate magmatism (~85 Ma), often during times of fast-migrating lithosphere. In contrast, East Asian-Russian ZIP sites reflect later basaltic magmatism (<40 Ma), often linked to episodes of back-arc rifting and spreading, slow-migrating lithosphere and slab subduction.
    Original languageEnglish
    Pages (from-to)399-420
    Number of pages22
    JournalMineralogy and Petrology
    Volume110
    Issue number45353
    DOIs
    Publication statusPublished - 2016

    Keywords

    • Asia, Pacific
    • basalt
    • crystals
    • lithosphere
    • uranium, lead dating
    • zircon

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