Journal of Petrology | Volume 38 | Number 10 | Pages 1331-1358 | 1997
© Oxford University Press 1997
Geochemical Variations in Vanuatu Arc Lavas: the Role of Subducted Material and a Variable Mantle Wedge Composition
1 Department of Geological Sciences, University of DurhamScience Laboratories, South Road, Durham DH1 3LE, UK
2 Department of Earth Sciences, The Open UniversityWalton Hall, Milton Keynes MK7 6AA, UK
3 Department of Geology, Oxford Brookes UniversityGipsy Lane, Headington, Oxford OX3 0BP, UK
4 Department of Terrestrial Magnetism, Carnegie Institution of Washington5241 Broad Branch Road, NW, Washington, DC 20015, USA
5 Geological Institute, University of Tokyo7–3-1 Hongo, Tokyo 113, Japan
6 Present address: HealthCanada, Bureau of Human Prescription DrugsTunneys Pasture, Ottawa, Ontario K1A OL2 Canada
Received March 31, 1995; Revised typescript accepted June 13, 1997
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Abstract |
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New compositional data are presented for recent (<3.5 Ma) basaltic lavas from the Vanuatu arc and North Fiji back-arc, and for material being subducted at the Vanuatu trench. Sr, Nd and Pb isotope data for the lavas vary systematically north–south along the arc and highlight where the D'Entrecasteaux Zone on the subducting plate collides with the fore-arc. Major and trace element data show significant lateral variations in enrichment of the mantle wedge relative to an N-MORB source. New elemental and isotopic analyses of the North Loyalty Basin sediments have allowed the flux of elements in the subducting sediments to be calculated. The wedge has been variably modified by addition of slab-derived material containing a significant subducted sediment component. Merelava in the rear-arc is anomalous and is dominated by a fluid component derived from subducted oceanic crust. Most lavas originate from a Pacific-MORB-like mantle source except for those erupting close to the collision zone in central Vanuatu. Collision of the D'Entrecasteaux Zone has disrupted the arc complex and brought less depleted, isotopically distinct (Indian-MORB-like) mantle material from the back-arc into the arc magma source in this region.
KEY WORDS: subduction; geochemistry; melting; sediments; fluxes
* Corresponding author at: Danish Lithosphere Centre, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark. Telephone: + 45 3814 2664. Fax: +45 33110878. E-mail: dwp{at}dlc.ku.dk
Present address: HealthCanada, Bureau of Human Prescription Drugs, Tunneys Pasture, Ottawa, Ont. K1A 0L2, Canada
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