Wade, Jennifer A. and Plank, Terry and Stern, Robert J. and Tollstrup, Darren L. and Gill, James B. and O'Leary, Julie C. and Eiler, John M. and Moore, Richard B. and Woodhead, Jon D. and Trusdell, Frank and Fischer, Tobias P. and Hilton, David R. (2005) The May 2003 eruption of Anatahan volcano, Mariana Islands: Geochemical evolution of a silicic island-arc volcano. Journal of Volcanology and Geothermal Research, 146 (1-3). pp. 139-170. ISSN 0377-0273 http://resolver.caltech.edu/CaltechAUTHORS:20121031-115035309
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The first historical eruption of Anatahan volcano began on May 10, 2003. Samples of tephra from early in the eruption were analyzed for major and trace elements, and Sr, Nd, Pb, Hf, and O isotopic compositions. The compositions of these tephras are compared with those of prehistoric samples of basalt and andesite, also newly reported here. The May 2003 eruptives are medium-K andesites with 59–63 wt.% SiO_2, and are otherwise homogeneous (varying less than 3% 2σ about the mean for 45 elements). Small, but systematic, chemical differences exist between dark (scoria) and light (pumice) fragments, which indicate fewer mafic and oxide phenocrysts in, and less degassing for, the pumice than scoria. The May 2003 magmas are nearly identical to other prehistoric eruptives from Anatahan. Nonetheless, Anatahan has erupted a wide range of compositions in the past, from basalt to dacite (49–66 wt.% SiO_2). The large proportion of lavas with silicic compositions at Anatahan (> 59 wt.% SiO_2) is unique within the active Mariana Islands, which otherwise erupt a narrow range of basalts and basaltic andesites. The silicic compositions raise the question of whether they formed via crystal fractionation or crustal assimilation. The lack of ^(87)Sr/^(86)Sr variation with silica content, the MORB-like δ^(18)O, and the incompatible behavior of Zr rule out assimilation of old crust, altered crust, or zircon-saturated crustal melts, respectively. Instead, the constancy of isotopic and trace element ratios, and the systematic variations in REE patterns are consistent with evolution by crystal fractionation of similar parental magmas. Thus, Anatahan is a type example of an island-arc volcano that erupts comagmatic basalts to dacites, with no evidence for crustal assimilation. The parental magmas to Anatahan lie at the low ^(143)Nd/^(144)Nd, Ba/La, and Sm/La end of the spectrum of magmas erupted in the Marianas arc, consistent with 1–3 wt.% addition of subducted sediment to the mantle source, or roughly one third of the sedimentary column. The high Th/La in Anatahan magmas is consistent with shallow loss of the top ∼ 50 m of the sedimentary column during subduction.
|Additional Information:||© 2005 Elsevier B.V. Received 18 July 2004; accepted 28 November 2004. We would like to thank Mike Cunningham of Americopters for transport to and from Anatahan during both the May 2003 and April 2004 sampling trips, as well as Alison Shaw for exceptional help in the field. Florencia Meana-Prado, Caitlin Masaric-Johnson, and Louise Bolge provided able analytic assistance. Useful comments from editor J. Pallister as well as reviewers B. Leeman and M. Reagan greatly strengthened this manuscript. This research was funded by NSF OCE 0001897 MARGINS to T. Plank, NSF OCE 0325189 to J. Gill, NSF OCE 0305218 MARGINS to T. Fischer, and NSF OCE 0305248 to D. Hilton.|
|Subject Keywords:||Anatahan volcano, Mariana Islands; geochemical evolution; island-arc volcano|
|Official Citation:||Jennifer A. Wade, Terry Plank, Robert J. Stern, Darren L. Tollstrup, James B. Gill, Julie C. O'Leary, John M. Eiler, Richard B. Moore, Jon D. Woodhead, Frank Trusdell, Tobias P. Fischer, David R. Hilton, The May 2003 eruption of Anatahan volcano, Mariana Islands: Geochemical evolution of a silicic island-arc volcano, Journal of Volcanology and Geothermal Research, Volume 146, Issues 1–3, 15 August 2005, Pages 139-170, ISSN 0377-0273, 10.1016/j.jvolgeores.2004.11.035. (http://www.sciencedirect.com/science/article/pii/S0377027305001058)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||31 Oct 2012 21:01|
|Last Modified:||31 Oct 2012 21:01|
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