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^(230)Th-^(238)U disequilibrium in island arcs: evidence from the Aleutians and the Marianas

Newman, S. and Macdougall, J. D. and Finkel, R. C. (1984) ^(230)Th-^(238)U disequilibrium in island arcs: evidence from the Aleutians and the Marianas. Nature, 308 (5956). pp. 268-270. ISSN 0028-0836. doi:10.1038/308268a0.

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Complex models for magma generation in island arcs have recently been proposed which require varying contributions from three possible sources: (1) the mantle; (2) subducted, altered oceanic crust; and (3) sediments (see, for example, refs 1–6). These models involve partial melting of metasomatized mantle. The metasomatizing liquids derive from the subducted slab and are large-ion-lithophile (LIL) element-bearing fluids or are themselves partial melts. Further modification of the chemical composition of the lavas may occur by processes such as shallow-level fractional crystallization. Because the Th/U ratio is quite different for each of the three possible magma sources mentioned above, and as Th and U may behave differently during fractionation processes, particularly if volatile transport is involved, studies of ^(230)Th–^(238)U disequilibrium have great potential in investigations of arc lavas. Our data, given here, imply that the Th/U ratio in the sources of Mariana and Aleutian Island Arc lavas is similar to ocean ridge basalt sources, although there is a hint of a somewhat lower Th/U component in the Aleutian source. The data also confirm and extend the observations by Gill and Allègre and Condomines that oceanic arc lavas are distinguished from magmas erupted in virtually all other volcanic environments by activity ratios (^(230)Th/^(238)U)⩽1, implying relative enrichment of uranium.

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Newman, S.0000-0003-0710-995X
Alternate Title:230Th–238U disequilibrium in island arcs: evidence from the Aleutians and the Marianas
Additional Information:© 1984 Springer Nature Limited. Received 2 August; accepted 7 December 1983. The authors thank the following for providing the samples studied in this project: Drs N. G. Banks, T. H. Dixon, R. Kay and R. J. Stern. This research was supported by NSF grants EAR8000484 and EAR8026448. SIO-IG^2L contribution 21.
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Issue or Number:5956
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90291
Deposited By: George Porter
Deposited On:17 Oct 2018 15:52
Last Modified:16 Nov 2021 03:31

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