Oxygen isotopes in Samoan lavas; confirmation of continent recycling

Lavas from the Samoan volcanic chain show the most enriched geochemical signatures ever documented in oceanic lavas (87Sr/86Sr as high as 0.7205). In order to test the hypothesis that their source contains a component of recycled upper continental crust, we measured oxygen isotope compositions of ol...

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Bibliographic Details
Published in:Geology (Boulder) 2008-07, Vol.36 (7), p.551-554
Main Authors: Workman, Rhea K, Eiler, John M, Hart, Stanley R, Jackson, Matthew G
Format: Article
Language:English
Subjects:
alkaline earth metals
chemical ratios
continental crust
correlation
crust
cycles
Geochemistry
Geology
hot spots
igneous and metamorphic rocks
Igneous rocks
isotope ratios
Isotopes
Lava
lead
mantle
Marine
metals
nesosilicates
O-18/O-16
Oceania
olivine
olivine group
orthosilicates
oxygen
Pb-207/Pb-204
Petrology
phenocrysts
Polynesia
radioactive isotopes
Samoa
Sedimentation & deposition
silicates
Sr-87/Sr-86
stable isotopes
strontium
trace elements
volcanic rocks
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Summary:Lavas from the Samoan volcanic chain show the most enriched geochemical signatures ever documented in oceanic lavas (87Sr/86Sr as high as 0.7205). In order to test the hypothesis that their source contains a component of recycled upper continental crust, we measured oxygen isotope compositions of olivine phenocrysts from these lavas. Correlations between δ18O of olivines (5.11 per mil-5.70 per mil) and 87Sr/86Sr and 207Pb/204Pb of whole rocks, as well as Ce/Pb and Nb/Th ratios of whole rocks, indicate that (1) measured δ18O are primary, mantle-derived values, and (2) the enriched mantle source of these lavas contains continental crust or its derivative sediments. The observed trend between δ18O and 87Sr/86Sr can be fit using either clastic marine sediment or continental crust values of δ18O, Sr concentration, and 87Sr/86Sr, but only those for clastic marine sediments are compatible with trace element modeling. We conclude that the enriched source for Samoan basalts was created by sedimentation of continent-derived material into a marine environment, followed by subduction and mixing with ambient mantle.
ISSN:0091-7613
1943-2682
DOI:10.1130/G24558A.1