Basalts from the Efate Island Group, central section of the Vanuatu Arc, SW Pacific; geochemistry and petrogenesis

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doi: 10.1016/j.jvolgeores.2003.12.004
Authors:Raos, Alison M.; Crawford, Anthony J.
Author Affiliations:Primary:
University of Tasmania, Centre for Ore Deposit Research, Hobart, Tasmania, Australia
Volume Title:Journal of Volcanology and Geothermal Research
Source:Journal of Volcanology and Geothermal Research, 134(1-2), p.35-56. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-0273
Publication Date:2004
Note:In English. 56 refs.; illus., incl. 3 plates, 3 tables, geol. sketch maps
Summary:Basalts of the Efate Island Group (<0.7 Ma) occur in the central part of the Vanuatu island arc between the "normal" southern section of the arc and the central part of the arc affected by collision with the Eocene D'Entrecasteaux Ridge. These basalts form small cones constructed upon a volcaniclastic apron principally composed of trachydacitic breccias. Temporal and compositional features allow identification of three basalt groups. Subtle compositional differences exist between two of these suites, whereas the third shows pronounced enrichment in K and Rb, with few differences for other elements. These variations are taken to record slight compositional variations in the ambient mantle wedge composition, with the high-K, high-Rb suite deriving from localised zones relatively enriched in phlogopite. Compared with other Vanuatu arc basalts, the Efate basalts show appreciable enrichment in Sr and P2O5. The Pb isotopic characteristics of the Efate basalts are commensurate with the transitional position of this island within the Vanuatu arc, between the southern arc lavas and those erupted in the region affected by D'Entrecasteaux Ridge collision. However, 87Sr/86Sr values (0.70387-0.70424) are slightly higher and 143Nd/144Nd values slightly lower than predicted by the spatial change of these values along the arc. These features are taken to indicate derivation of the Efate basalts from a local, unusual mantle source. Two contrasting models are considered to account for the unusual features of the source mantle of these basalts. Model 1 suggests that the high Sr and P2O5 characteristics of the peridotite source of the Efate basalts were produced by subduction of an intraplate volcano similar to ORSTOM seamount, currently subducting immediately northwest of Efate. Recent studies have demonstrated massive P2O5 and Sr enrichments in highly altered formerly glassy seamount lavas and hyaloclastites. Model 2 proposes that the ambient strongly depleted mantle wedge has been locally modified by carbonatite metasomatism. A well-defined tear or gap in the subducted slab beneath the Efate sector of the Vanuatu arc may have provided appropriate conditions for production of an ephemeral carbonatite partial melt from asthenosphere convecting into the hole in the slab. This melt invaded the mantle wedge, stamping enrichment of Sr and P2O5 on a mantle wedge peridotite that had already been metasomatised by fluids derived from sediments on the subducting plate. Abstract Copyright (2004) Elsevier, B.V.
Sections:Geochemistry; Petrology
Subjects:Alkaline earth metals; Basalts; Breccia; Carbonatites; Cenozoic; Chemical composition; Cones; Enrichment; Eocene; Geochemistry; ICP mass spectra; Igneous rocks; Island arcs; Isotope ratios; Isotopes; Magmatism; Major elements; Mantle; Mass spectra; Metals; Mid-ocean ridges; Mineral composition; Models; Nd-144/Nd-143; Neodymium; Ocean floors; Pacific Plate; Paleogene; Petrography; Plate tectonics; Rare earths; Spectra; Sr-87/Sr-86; Stable isotopes; Strontium; Subduction; Tertiary; Trace elements; Volcanic features; Volcanic rocks; Volcanism; X-ray fluorescence spectra; Melanesia; North Fiji Basin; Oceania; Pacific Ocean; South Pacific; Southwest Pacific; Vanuatu; West Pacific; D'Entrecasteaux Ridge; Efate Island Group
Coordinates:S203000 S130000 E1690000 E1660000
Abstract Numbers:04M/4934
Record ID:2007043250
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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