G3: Geochemistry, Geophysics, Geosystems
DOI of Published Version
[I] We report 23RU_230Th_226Ra_21Ilpb_2IOpo, 232Th_32SRa and 235UJl1Pa measurements for a suite of 14 geologically and geochemically well-characterized basaltic sanlples from the Samoan volcanoes Vailulu'u, Malumalu, and Savai'i. Maximum eruption ages based on the presence of parent-daughter disequilibria indicate that Vailulu 'u is magmatically productive with young lavas «8 Ka) resurfacing both its sunmlit crater and lower flanks. 311lpb and 21 'To measurements indicate that several flows have erupted within its sunmrit crater in the past 100 years, with the newest observed flow being erupted in November of 2004. For lavas which have eruption ages that are demonstrably young, relative to the half-lives of 23( lTh, 231Pa and 226Ra we interpret their 23SU _DoTh n'U_23IPa and 230Th - 22(iRa disequilibria in ternlS of the magn~atic proce~ses occurring beneath the Samoan Islands. c"31IThP"U) > i indicates that g~et is required as a residual phase in the magma sources for all these lavas. The large range of c'''Ul''l"Th) and e"'Thj232Th) is attributed to long-ternl source variation. The Samoan basalts are all a1lcaline basalts and show significant 23°Th and Cl'Pa excesses but limited variabilil);', indicating that they have been derived by small but similar extents of melting. Their ("'ThP"U), C"PaF"U) and SmlNd fractionation are consistent with correlations anl0ng other ocean island basalt suites (particularly Hawaii) which show that eOThP3RU) and c" 31 PaP35U) of many OIBS can be explained by sinlple tinle-independent models. Interpretation of the""'Ra data requires tinle-dependent melting models. Both chromatographic porous flow and dynanlic melting of a garnet peridotite source can adequately explain the combined U-Th-Ra and U-Pa data for these Sanl0an basalts. Several young sanlples from the Vailulu'u sunmlit crater also exhibit significant 2 IOPb deficits that r~flect eith~r shallow magmati<; .Erocesses. or continuous magma degassing. In both cases, decadal residence tmles are mferred from these -, "Pb deficits. The young coeval volcamsm on Malun13lu and Vailulu'u suggests the SanlOa hot spot is currently migrating to the northeast due to dynanlic interaction with the Tonga slab.
sustainability, U-series disequilibria, Samoa, eruption ages
Journal Article Version
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Published Article/Book Citation
G3, 9:4(2008), pp. 1-30. www.agu.org/journals/gc/
Copyright © AGU and the Geochemical Society, 2008. Posted by permission.