Compositional and textural variation of Surtur I tephra crater through the Surtsey eruption, Iceland, 1963-1967

Bush-Marcinowski, Tim

Holocene explosive surtseyan volcanism on the southern most tip of the Vestmannaeyjar archipelago is reported and discussed. Subaerial tuff and tephra deposits recording a 180m thickness retrieved from a borehole are analysed from one of the two active explosive craters during the formation of the island of Surtsey. A range of minerologies, coarseness, porosities, alteration and densities are encountered throughout the volcanic pile, highlighting the non-­‐uniform nature of deposits due to post volcanic processes. Additionally, the presence of shear planes, concentric subsidence faults, accretionary lappili, tuff vesicles and scoraceous fragments infer mass flow processes operating within the crater. The geochemical variation of glass grains and a few olivine penocrysts are analysed from new subsamples. Primarily a non-­‐variation in major elements exists throughout the borehole, with change only observed within the initial stages of eruptions. An average vesicularity range of 40-­‐50% exists in most samples, consistent with other surtseyan volcanic eruption ranges. These characteristics together infer a closed-­‐system magma chamber complex beneath the Surtsey region with normal fractional crystallization. The magma batch that produced all satellite vents is relatively homogenous with whole rock variation minimal.

90 pages A4

2014Bush-Marcinowski

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