title: The Surtsey Magma Series.
abstract: The volcanic island of Surtsey (Vestmannaeyjar, Iceland) is the product of a 3.5-year-long eruption that began in November 1963. Observations of magma-water interaction during pyroclastic episodes made Surtsey the type example of shallow-to-emergent phreatomagmatic eruptions. Here, in part to mark the 50(th) anniversary of this canonical eruption, we present previously unpublished major-element whole-rock compositions, and new major and trace-element compositions of sideromelane glasses in tephra collected by observers and retrieved from the 1979 drill core. Compositions became progressively more primitive as the eruption progressed, with abrupt changes corresponding to shifts between the eruption's four edifices. Trace-element ratios indicate that the chemical variation is best explained by mixing of different proportions of depleted ridge-like basalt, with ponded, enriched alkalic basalt similar to that of Iceland's Eastern Volcanic Zone; however, the systematic offset of Surtsey compositions to lower Nb/Zr than other Vestmannaeyjar lavas indicates that these mixing end members are as-yet poorly contained by compositions in the literature. As the southwestern-most volcano in the Vestmannaeyjar, the geochemistry of the Surtsey Magma Series exemplifies processes occurring within ephemeral magma bodies on the extreme leading edge of a propagating off-axis rift in the vicinity of the Iceland plume.
authors.affiliation: School of Geography, Environment and Earth Sciences, Victoria University, PO Box 600, Wellington 6140, New Zealand.
authors.forename: C Ian
authors.initials: CI
authors.lastname: Schipper
authors.affiliation: Icelandic Institute of Natural History, Urridaholtsstraeti 6-8, 210 Gardabaer, Iceland.
authors.forename: Sveinn P
authors.initials: SP
authors.lastname: Jakobsson
authors.affiliation: Geology Department, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
authors.forename: James D L
authors.initials: JD
authors.lastname: White
authors.affiliation: Geology Department, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
authors.forename: J
authors.initials: J
authors.lastname: Michael Palin
authors.affiliation: Geology Department, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
authors.forename: Tim
authors.initials: T
authors.lastname: Bush-Marcinowski