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Published May 30, 2008 | public
Journal Article

Insights into the origin of low-δ^(18)O basaltic magmas in Hawaii revealed from in situ measurements of oxygen isotope compositions of olivines

Abstract

In situ measurements of oxygen isotope and elemental compositions of olivines from subaerial Mauna Kea lavas reveal that their δ^(18)O values correlate positively with their forsterite contents, consistent with addition of one or more low-δ^(18)O components into magmas from which they grew over the course of their crystallization–differentiation histories. This result supports previous suggestions that low-δ^(18)O components to Mauna Kea lavas are contaminants derived from hydrothermally-altered rocks in the volcanic edifice or lithosphere, rather than components of the underlying mantle sources of these lavas. The slope of the correlation between δ^(18)O values and forsterite contents of olivines is steeper for subaerial Mauna Kea lavas than for submarine Mauna Kea lavas, and olivines from Mauna Loa lavas exhibit negligible changes in δ^(18)O values over a similar range of forsterite contents. Models of assimilation–fractional crystallization (AFC) processes can explain our observations if the δ^(18)O values of crustal contaminants decrease sharply at the submarine–subaerial transition in Mauna Kea volcano, and if Mauna Loa lavas are either uncontaminated or contaminated only by rocks that have δ^(18)O values similar to that of primary Mauna Loa magmas. We suggest that the differences in oxygen isotope systematics among Mauna Loa, submarine Mauna Kea and subaerial Mauna Kea lavas principally reflect the sources and amounts of water available to hydrothermal systems in the volcanic edifice.

Additional Information

© 2008 Elsevier B.V. Received 26 December 2006; received in revised form 25 January 2008; accepted 1 February 2008. Available online 4 March 2008. Edited by: R.W. Carlson. We thank Chi Ma for helps with SEM and EMP analysis in the Caltech GPS analytical facility, George Rossman for discussions and providing gem-quality San Carlos olivine standard, Paul Asimow for teaching the first author to use the MELTS program, and H.P. Taylor and K. Muehlenbachs for providing valuable comments. This paper is also greatly benefited from comments and suggestions from Dr. Danny Rye, Richard Carlson, and 2 anonymous reviewers. The principle financial support for this research was a grant from the Margins program at NSF.

Additional details

Created:
August 22, 2023
Modified:
October 20, 2023