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Helium isotopic composition of the Tabar-Lihir-Tanga-Feni island arc, Papua New Guinea

Patterson, D. B. and Farley, K. A. and McInnes, B. I. A. (1997) Helium isotopic composition of the Tabar-Lihir-Tanga-Feni island arc, Papua New Guinea. Geochimica et Cosmochimica Acta, 61 (12). pp. 2485-2496. ISSN 0016-7037. doi:10.1016/S0016-7037(97)00095-1.

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Helium abundances and isotopic ratios have been measured in samples of geothermal gases, submarine ultramafic xenoliths, and subaerial mafic phenocrysts and xenoliths from the Tabar-LihirTanga-Feni (TLTF) arc in the Bismarck Archipelago of Papua New Guinea. These unusual volcanoes are produced by adiabatic decompression melting of subduction-modified upper mantle and apparently carry an exceptionally large slab-derived component. They, therefore, provide an ideal setting for studying the role of subducted helium in arc volcanoes. Helium isotopic ratios in the geothermal fluids, submarine xenoliths, and most helium-rich subaerial samples indicate the mantle source regions beneath the Tabar Island Group and Lihir Island have ^3He/^4He ratios of about 7.2 times the atmospheric ratio (R_A), whereas the mantle source for Ambitle Island (Feni Group) in the more southern TLTF arc has a lower ratio of about 6.6 R_A. These ratios are only slightly lower than typical depleted upper mantle values of about 8.5 R_A, indicating that even severely slab-modified mantle wedge carries a relatively minor slab-derived helium component. The systematically lower ^3He/^4He ratios of the Ambitle samples are interpreted to reflect a slightly greater slab-derived helium component. Helium isotopic ratios as low as 2 R_A, which are correlated with low total helium abundances, were observed in subaerial augitic clinopyroxene phenocrysts. Coexisting olivine and sodium-rich acmitic clinopyroxene have higher helium abundances and isotopic ratios. This isotopic disequilibrium between coexisting mineral phases is interpreted as crustal-level addition of a low ^3He/^4He component to an actively outgassing magma from which different mineral phases trap helium sequentially.

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Farley, K. A.0000-0002-7846-7546
Additional Information:© 1997 Elsevier Science Ltd. Received July 22, 1996; accepted in revised form February 18, 1997. Editorial handling: U. Ott. We wish to thank the Lihir Management Company, Nord Pacific Ltd., and Father Anthony Gendusa for providing invaluable assistance in the collection of the subaerial samples and Master M. Kull and the officers and crew of R.V. SONNE for assistance collecting the submarine samples during EDISON Cruise SO-94. We thank also M. Perfit for reference to unpublished data. We are also indebted to D. Hilton and two anonymous reviewers for their very helpful suggestions. This work was supported by NSF OCE-9402159 to KAF.
Group:UNSPECIFIED, Division of Geological and Planetary Sciences
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Issue or Number:12
Record Number:CaltechAUTHORS:20121120-144917367
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Official Citation:D.B. Patterson, K.A. Farley, B.I.A. McInnes, Helium isotopic composition of the Tabar-Lihir-Tanga-Feni island arc, Papua New Guinea, Geochimica et Cosmochimica Acta, Volume 61, Issue 12, June 1997, Pages 2485-2496, ISSN 0016-7037, 10.1016/S0016-7037(97)00095-1. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35585
Deposited By: Ruth Sustaita
Deposited On:20 Nov 2012 23:05
Last Modified:09 Nov 2021 23:16

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