Kent, Adam J. R. and Clague, David A. and Honda, Masahiko and Stolper, Edward M. and Hutcheon, Ian D. and Norman, Marc D. (1999) Widespread assimilation of a seawater-derived component at Loihi Seamount, Hawaii. Geochimica et Cosmochimica Acta, 63 (18). pp. 2749-2761. ISSN 0016-7037 http://resolver.caltech.edu/CaltechAUTHORS:20120822-125024224
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Many tholeiitic and transitional pillow-rim and fragmental glasses from Loihi seamount, Hawaii, have high Cl contents and Cl/K_2O ratios (and ratios of Cl to other incompatible components, such as P_2O_5, H_2O, etc.) relative to other Hawaiian subaerial volcanoes (e.g., Mauna Loa, Mauna Kea, and Kilauea). We suggest that this results from widespread contamination of Loihi magmas by a Cl-rich, seawater-derived component. Assimilation of high-Cl phases such as saline brine or Cl-rich minerals (halite or iron–hydroxychlorides) with high Cl/H_2O ratios can explain the range and magnitude of Cl contents in Loihi glasses, as well as the variations in the ratios of Cl to other incompatible elements. Brines and Cl-rich minerals are thought to form from seawater within the hydrothermal systems associated with submarine volcanoes, and Loihi magmas could plausibly have assimilated such materials from the hydrothermal envelope adjacent to the magma chamber. Our model can also explain semiquantitatively the observed contamination of Loihi glasses with atmospheric-derived noble gases, provided the assimilant has concentrations of Ne and Ar comparable to or slightly less than seawater. This is more likely for brines than for Cl-rich minerals, leading us to favor brines as the major assimilant. Cl/Br ratios for a limited number of Loihi samples are also seawater-like, and show no indication of the higher values expected to be associated with the assimilation of Cl-rich hydrothermal minerals. Although Cl enrichment is a common feature of lavas from Loihi, submarine glasses from other Hawaiian volcanoes show little (Kilauea) or no (Mauna Loa, Mauna Kea) evidence of this process, suggesting that assimilation of seawater-derived components is more likely to occur in the early stages of growth of oceanic volcanoes. Summit collapse events such as the one observed at Loihi in October 1996 provide a ready mechanism for depositing brine-bearing rocks from the volcanic edifice into the top of a submarine summit magma chamber.
|Additional Information:||© 1999 Elsevier Science Ltd. Received 4 February 1999. Revised 8 June 1999. Accepted 8 June 1999. Available online 18 October 1999. The authors thank P. Valbracht and A. Malahoff for samples and P. Carpenter and D. Phinney for help with analyses. Comments by A. Jambon and M. Palin and reviews by M. Garcia and P. Michael improved the quality of this contribution. We also thank Professor A. Jambon for sharing unpublished data. Supported by NSF grant EAR95-28594 and DOE grant DE-FG03-85ER13445. Performed under the auspices of the DOE by LLNL under contract W-7405-Eng-48. Division of Geological and Planetary Science contribution 5708.|
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|Official Citation:||Adam J.R Kent, David A Clague, Masahiko Honda, Edward M Stolper, Ian D Hutcheon, Marc D Norman, Widespread assimilation of a seawater-derived component at Loihi Seamount, Hawaii, Geochimica et Cosmochimica Acta, Volume 63, Issue 18, September 1999, Pages 2749-2761, ISSN 0016-7037, 10.1016/S0016-7037(99)00215-X.|
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|Deposited By:||Aucoeur Ngo|
|Deposited On:||22 Aug 2012 20:29|
|Last Modified:||22 Aug 2012 20:29|
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