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Hf isotopic evidence for small-scale heterogeneity in the mode of mantle wedge enrichment: Southern Havre Trough and South Fiji Basin back-arcs

Record type: Article

Magmas from SW Pacific back-arc basins have geochemical and isotopic signatures indicating variable mantle and subduction-derived components. Basalts from South Fiji Basin (SFB) are little influenced by subduction, but come from variably enriched mantle, resulting from mixing between enriched mantle, like FOZO, and depleted mantle, like DMM. The same components are present in the Havre Trough mantle, but Havre Trough basalts come from a mantle wedge to which a greater proportion of subduction-derived components are added. Their slab-derived components are isotopically similar to locally subducting sediment, with variable Sr and Pb from altered oceanic crust. Their compositional diversity correlates with morphology, previously described as contrasting Arc-type and Rift-type back-arc regimes. Geochemical modeling indicates that material is added as both supercritical fluids and slab melts below the back-arc, is locally distinct, and correlate with differences in the predicted slab-surface pressure and temperature conditions. Deeper slab surfaces correspond to higher-temperatures at a given distance from the volcanic front, but not necessarily with an increase in the amount of slab-derived material. Slab fluxes for rift-type basalts are consistent with predicted slab-surface temperatures at or below the water-saturated solidus. However, some are consistent with melting in equilibrium with residual rutile, zircon, and monazite, so melting may have occurred by fluid fluxing of the slab surface, requiring external fluids from within the slab. Arc-type basalts are explained by thermal anomalies in the mantle wedge, which may correspond to locally hotter slab-surface temperatures and more fractionated slab-derived component signatures in their source.

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Citation

Todd, Erin, Gill, James, Wysoczanski, Richard J., Hergt, Janet, Wright, Ian Craig, Leybourne, Matthew I and Mortimer, Nick (2011) Hf isotopic evidence for small-scale heterogeneity in the mode of mantle wedge enrichment: Southern Havre Trough and South Fiji Basin back-arcs Geochemistry Geophysics Geosystems, 12, (9), Q09011. (doi:10.1029/2011GC003683).

More information

Accepted/In Press date: July 2011
Published date: 2011
Organisations: Marine Geoscience

Identifiers

Local EPrints ID: 195835
URI: http://eprints.soton.ac.uk/id/eprint/195835
ISSN: 1525-2027
PURE UUID: 07d834b6-8c9d-4a24-82c0-5a12cf4c8075

Catalogue record

Date deposited: 30 Aug 2011 11:01
Last modified: 18 Jul 2017 11:24

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Contributors

Author: Erin Todd
Author: James Gill
Author: Richard J. Wysoczanski
Author: Janet Hergt
Author: Ian Craig Wright
Author: Matthew I Leybourne
Author: Nick Mortimer

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