RESEARCH ARTICLE Degassing and magma mixing during the eruption of Surtsey Volcano (Iceland, 1963–1967): the signatures of a dynamic and discrete rift propagation event C. Ian Schipper 1,2 & Marion Le Voyer 3,4 & Yves Moussallam 5 & James D. L. White 6 & Thor Thordarson 7 & Jun-Ichi Kimura 2 & Qing Chang 2 Received: 30 October 2015 /Accepted: 16 March 2016 /Published online: 29 March 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract The eruption of Surtsey (Iceland, 1963–1967) is a rare example of observed volcanism at a propagating rift tip, where Iceland’ s Eastern Volcanic Zone is advancing south- westerly toward the Reykjanes Ridge. We use olivine-hosted melt inclusions, embayments, and matrix glasses to investi- gate major element, trace element, and volatile characteristics of Surtsey’ s magmatic system, and to parameterize decom- pression models that describe degassing of C-H-S-O species during this well-studied eruption. Major elements show that the inclusions represent heterogeneous melts with a range of compositions similar to those of Icelandic lavas. Trace ele- ments discriminate between two groups of inclusions: the ma- jority are compositionally similar to Eastern Volcanic Zone alkalic basalts, and the remainder are notably more depleted in incompatible trace elements and trend toward fields defined by tholeiites on and around Iceland. Strongly correlated Cl and Nb for all inclusions indicates that seawater did not affect Surtsey’ s volatile budget, despite having clearly affected its eruption style. Both types of inclusions are volatile rich ( ≤ 1.47 wt.% H 2 O; ≤ 2534 ppm CO 2 as measured or ≤5286 ppm once corrected for vapor bubbles and post- entrapment crystallization). They are more hydrous than pri- mary melts in the onshore Eastern Volcanic Zone and have parental CO 2 /Nb (≤590) at the upper end of regional esti- mates. Saturation pressures calculated from corrected CO 2 values indicate that melts in both inclusion types initially crys- tallized at similar depths in the upper mantle (17–21 km), and then partially crystallized during ascent through the lower crust (7–13 km). Historical data show that gases emitted on Surtsey shifted from being relatively reduced in 1964/1965 to more oxidized in 1967, after a protracted period of effusive activity and resurgence of pyroclastic activity from satellite vents. Closed-system degassing models predict the composi- tions and redox states of the 1964/1965 gases extremely well, but cannot account for the oxidized gases emitted in 1967, which may have been contaminated by ambient air in a system Editorial responsibility: P.Wallace, acting Executive Editor Electronic supplementary material The online version of this article (doi:10.1007/s00445-016-1025-4) contains supplementary material, which is available to authorized users. * C. Ian Schipper schipper.ian@gmail.com 1 School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand 2 Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan 3 Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA 4 Department of Geology, University of Maryland, College Park, MD 20742, USA 5 SCRIPPS Institution of Oceanography, 8622 Kennel Way, La Jolla, CA 92037, USA 6 Geology Department, University of Otago, PO Box 56, Leith Street, Dunedin 9016, New Zealand 7 Faculty and Institute of Earth Sciences, University of Iceland, Sturlugötu 7, 101 Reykjavík, Iceland Bull Volcanol (2016) 78: 33 DOI 10.1007/s00445-016-1025-4