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Published October 30, 2005 | metadata_only
Journal Article

Oxygen–osmium isotope systematics of West Maui lavas: A record of shallow-level magmatic processes


New δ^(18)O and ^(187)Os/^(188)Os data from late shield-building stage lavas from West Maui volcano, Hawai'i, indicate that a range of distinct shallow-level processes can affect compositions of plume-generated ocean island magmas. The relative ages of the samples studied were determined either on the basis of field relationships, or from collection depth in a water well. The stratigraphically lower lavas have [Os] = 61–399 ppt, initial ^(187)Os/^(188)Os = 0.1311–0.1324 and δ^(18)O_(olivine) = 4.53–4.88‰. The stratigraphically higher lavas have [Os] = 20–273 ppt, initial ^(187)Os/^(188)Os = 0.1323–0.1390 (with the exception of one low [Os] sample with ^(187)Os/^(188)Os = 0.1517), and δ^(18)O_(olivine) = 4.73–5.21‰. These compositions are generally similar to those of Kea-type Hawaiian lavas from Mauna Kea and Kilauea volcanoes, but in detail, there are some significant differences between the West Maui lavas and other Kea-type lavas. The stratigraphically lower lavas have ^(187)Os/^(188)Os similar to those previously observed for Mauna Kea and Kilauea lavas, and define a nearly flat ^(87)Sr/^(86)Sr vs. ^(187)Os/^(188)Os trend that is consistent with assimilation by these magmas of small degree melts of Pacific oceanic crustal gabbros. The stratigraphically higher West Maui lavas extend to ^(187)Os/^(188)Os higher than observed at Mauna Kea or Kilauea. This probably results from interaction of these magmas with the hydrothermally altered volcanic edifice during the waning phases of the shield building stage. This process is likely to affect the isotope systematics of Os and O, but will have little effect on those of Hf, Nd, Pb or Sr.

Additional Information

© 2005 Elsevier B.V. Received 5 November 2004; received in revised form 22 July 2005; accepted 29 July 2005. Available online 30 September 2005. Editor: K. Farley. We thank Victor Kress for discussion on the behavior of sulfides in the mantle and during melt generation processes. We thank Glenn Bauer for providing the Mahinahina Well samples, and David Sherrod for collaboration on field efforts. We also thank Catherine Zimmermann for assistance with the Re and Os analyses. Marc Norman and Dominique Weis provided helpful reviews. This work was supported by a Geological Society of America Harold T. Stearns grant, a DOSECC Internship grant and a UW Graduate Research grant to AMG.

Additional details

August 22, 2023
August 22, 2023