Dredged igneous rocks from the northern termination of the Tofua magmatic arc, Tonga and adjacent Lau Basin

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Authors:Falloon, T. J.; Green, D. H.; Crawford, A. J.
Author Affiliations:Primary:
Univ. Tasmania, Dep. Geol., Hobart, Tasmania, Australia
Volume Title:Australian Journal of Earth Sciences
Source:Australian Journal of Earth Sciences, 34(4), p.487-506. Publisher: Blackwell, Melbourne, Victoria, Australia. ISSN: 0812-0099
Publication Date:1987
Note:In English. 47 refs.; illus. incl. 5 tables, sect., sketch maps
Summary:Fresh 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 petrogrphically and geochemically from boninites in their high CaO/Al2O3 ratios (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. [A.W.H.]
Subjects:Alkaline earth metals; Andesites; Boninite; Composition; Igneous rocks; Lava; Magnesium; Metals; Ophiolite; Petrology; Pillow lava; Volcanic rocks; East Pacific; Fiji; Lau Basin; Melanesia; Oceania; Pacific Ocean; Polynesia; South Pacific; Southeast Pacific; Tofua; Tonga; Lau-Colville Ridge
Abstract Numbers:88M/6299
Record ID:1988029981
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by Institute of Geological and Nuclear Sciences Limited (GNS Science), Lower Hutt, New Zealand
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