1Dept. of Earth Sciences, CEMPEG, Uppsala University, Sweden
2Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy
3Institute of Geosciences, University of Bremen, Germany
4Dept. of Earth and Planetary Sciences, McGill University, Canada
5Laboratory for Isotope Geology, Swedish Museum of Natural History, Stockholm, Sweden
6Dept. of Physics (Geology), GEOVOL, University of Las Palmas, Gran Canaria, Spain
7Dept. of Earth and Environmental Sciences, Ludwig-Maximilians Universität (LMU), Munich, Germany
8Leibniz-Institute for Oceanography, IFM-GEOMAR, Kiel, Germany
9Geological Survey of Sweden, Uppsala, Sweden
10School of Geographical and Earth Sciences, University of Glasgow, UK
11Department of Geological Sciences, University of Cape Town, South Africa
12SYRMEP Group, Sincrotrone Trieste S.C.p.A, Basovizza, Trieste, Italy
13Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, 56124 Pisa, Italy
Received: 18 Nov 2011 – Discussion started: 01 Dec 2011
Abstract. A submarine eruption started off the south coast of El Hierro, Canary Islands, on 10 October 2011 and continues at the time of this writing (February 2012). In the first days of the event, peculiar eruption products were found floating on the sea surface, drifting for long distances from the eruption site. These specimens, which have in the meantime been termed "restingolites" (after the close-by village of La Restinga), appeared as black volcanic "bombs" that exhibit cores of white and porous pumice-like material. Since their brief appearance, the nature and origin of these "floating stones" has been vigorously debated among researchers, with important implications for the interpretation of the hazard potential of the ongoing eruption. The "restingolites" have been proposed to be either (i) juvenile high-silica magma (e.g. rhyolite), (ii) remelted magmatic material (trachyte), (iii) altered volcanic rock, or (iv) reheated hyaloclastites or zeolite from the submarine slopes of El Hierro. Here, we provide evidence that supports yet a different conclusion. We have analysed the textures and compositions of representative "restingolites" and compared the results to previous work on similar rocks found in the Canary Islands. Based on their high-silica content, the lack of igneous trace element signatures, the presence of remnant quartz crystals, jasper fragments and carbonate as well as wollastonite (derived from thermal overprint of carbonate) and their relatively high oxygen isotope values, we conclude that "restingolites" are in fact xenoliths from pre-island sedimentary layers that were picked up and heated by the ascending magma, causing them to partially melt and vesiculate. As they are closely resembling pumice in appearance, but are xenolithic in origin, we refer to these rocks as "xeno-pumice". The El Hierro xeno-pumices hence represent messengers from depth that help us to understand the interaction between ascending magma and crustal lithologies beneath the Canary Islands as well as in similar Atlantic islands that rest on sediment-covered ocean crust (e.g. Cape Verdes, Azores). The occurrence of "restingolites" indicates that crustal recycling is a relevant process in ocean islands, too, but does not herald the arrival of potentially explosive high-silica magma in the active plumbing system beneath El Hierro.
Revised: 27 Feb 2012 – Accepted: 27 Feb 2012 – Published: 13 Mar 2012
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Troll, V. R., Klügel, A., Longpré, M.-A., Burchardt, S., Deegan, F. M., Carracedo, J. C., Wiesmaier, S., Kueppers, U., Dahren, B., Blythe, L. S., Hansteen, T. H., Freda, C., Budd, D. A., Jolis, E. M., Jonsson, E., Meade, F. C., Harris, C., Berg, S. E., Mancini, L., Polacci, M., and Pedroza, K.: Floating stones off El Hierro, Canary Islands: xenoliths of pre-island sedimentary origin in the early products of the October 2011 eruption, Solid Earth, 3, 97-110, doi:10.5194/se-3-97-2012, 2012.