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Dredged igneous rocks from the northern termination of the Tofua magmatic arc, Tonga and adjacent Lau Basin
journal contribution
posted on 2023-05-18, 08:25 authored by Trevor FalloonTrevor Falloon, David GreenDavid Green, Anthony CrawfordAnthony CrawfordFresh igneous rocks were dredged from six stations during the 1984 cruise of the Natsushima to the North Tonga Ridge and Lau Basin. Samples were recovered from inner trench wall, forearc, arc ridge and backarc basin settings in water depths >2000 m. The volcanics are unlike those of the subaerial volcanoes of the Tofua magmatic arc, and provide a glimpse of the petrological diversity present in the submarine levels of this intra‐oceanic arc‐backarc system. Amongst the dredged lavas are unusual olivine‐ and pyroxene‐bearing vitrophyres with high‐MgO (13–20 wt%) and SiO2 (52–56 wt%) contents. These primitive lavas are distinct petrographically and geochemically from boninites in their high CaO/Al2O3ratios (0.7–0.9), high‐CaO (>7 wt%) contents, and the presence of abundant olivine phenocrysts, but are similar to low‐Ti ophiolitic basalts such as those of the Upper Pillow Lavas of the Troodos ophiolite, Cyprus. The dredged Tongan high‐Mg lavas are therefore an in situ occurrence of a low‐Ti ophiolitic lava suite, and support an intra‐oceanic island arc origin for the Troodos and other ophiolites with these lavas.
History
Publication title
Australian Journal of Earth SciencesVolume
34Issue
4Pagination
487-506ISSN
0812-0099Department/School
School of Natural SciencesPublisher
Blackwell Publishing AsiaPlace of publication
54 University St, P O Box 378, Carlton, Australia, Victoria, 3053Repository Status
- Restricted