Computer Science
Scientific paper
Oct 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009e%26psl.287..519j&link_type=abstract
Earth and Planetary Science Letters, Volume 287, Issue 3-4, p. 519-528.
Computer Science
5
Scientific paper
We report the first neon isotope measurements on phenocrysts from subaerial and submarine Samoan lavas. These new data complement existing Ne-isotope data from Samoan peridotite xenoliths (Poreda, R.J., Farley, K.A.,1992. Rare gases in Samoan xenoliths. Earth Planet. Sci. Lett. 113, 689 129-144). Neon isotopes were measured in magmatic phenocrysts separated from nine shield-stage lavas from 5 Samoan volcanoes, including Ofu, Ta'u, Vailulu'u, Malumalu and Savai'i. Phenocrysts from subaerial Samoan lavas have higher 20Ne/22Ne than submarine phenocrysts, which may suggest different atmospheric contamination mechanisms for these two different eruptive environments. Olivine phenocrysts from a subaerial Ta'u lava exhibit the highest 20Ne/22Ne (11.33±0.08, 1σ) value in this study. Two subaerial Samoan samples from Ofu Island with high 3He/4He ratios (Ofu-04-06 and Ofu-04-03; 34 and 24 Ra [ratio to atmosphere], respectively) also have elevated 20Ne/22Ne ratios relative to air, and in a three-isotope neon plot the Ofu samples are indistinguishable from measurements made on high 3He/4He lavas from Hawaii, Iceland and Galapagos. The similarity of helium and neon isotopes in Ofu and Hawaii-Iceland-Galapagos is remarkable given the distinctions in 87Sr/86Sr (0.70458 for Ofu vs. 0.70329-0.70368 for Hawaii-Iceland-Galapagos) and 143Nd/144Nd (Ofu's 0.51283 vs. 0.51294-0.51297 for Hawaii-Iceland-Galapagos) in high 3He/4He lavas from these localities. Thus, the occurrence of similar helium and neon isotope compositions in lavas from these 4 hotspots does not appear to be linked to their variable Sr and Nd isotope compositions, and demonstrates a complex relationship between the isotopes of noble gases and the more refractory radiogenic isotopes. Additionally, we observe strongly nucleogenic neon isotopes in one the most isotopically-enriched (87Sr/86Sr > 0.718) Samoan lavas. This observation is consistent with the presence of recycled, continentally-derived marine sediment in the mantle source of the most enriched lavas from Samoa.
Hart Stanley R.
Jackson Matthew G.
Kurz Mark D.
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