Journal
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
Volume 15, Issue 4, Pages 986-1008Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2013GC005061
Keywords
mantle geochemistry; magma processes; isotope geochemistry; Lau Basin
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Funding
- NSF [OCE-1061134, OCE-1153894, EAR-1145202]
- French Agence Nationale de la Recherche [ANR-10-BLANC-0603]
- Directorate For Geosciences [1430610, 1358875] Funding Source: National Science Foundation
- Division Of Earth Sciences [1430610] Funding Source: National Science Foundation
- Division Of Ocean Sciences [1358875] Funding Source: National Science Foundation
- Division Of Ocean Sciences
- Directorate For Geosciences [1419915, 1232985] Funding Source: National Science Foundation
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Geochemical enrichment of lavas in the northern Lau Basin may reflect the influx of Samoan-plume mantle into the region. We report major and trace element abundances and He-Sr-Nd-Hf-Pb-isotopic measurements for 23 submarine volcanic glasses covering 10 locations in the northern Lau and North Fiji Basins, and for three samples from Wallis Island, which lies between Samoa and the Lau Basin. These data extend the western limit of geochemical observations in the Basins and improve the resolution of North-South variations in isotopic ratios. The Samoan hot spot track runs along the length of the northern trace of the Lau and North Fiji Basins. We find evidence for a Samoan-plume component in lavas as far West as South Pandora Ridge (SPR), North Fiji Basin. Isotopic signatures in SPR samples are similar to those found in Samoan Upolu shield lavas, but show a slight shift toward MORB-like compositions. We explain the origin of the enriched signatures by a model in which Samoan-plume material and ambient depleted mantle undergo decompression melting during upwelling after transiting from beneath the thick Pacific lithosphere to beneath the thin lithosphere in the northern Lau and North Fiji Basins. Other lavas found in the region with highly depleted isotopic signatures may represent isolated pockets of depleted mantle in the basins that evaded this enrichment process. We further find that mixing between the two components in our model, a variably degassed high-He-3/He-4 Samoan component and depleted MORB, can explain the diversity among geochemical data from the northern Lau Basin.
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