Solid Earth Discussions www.solid-earth-discuss.net 1869-9537 3 2 2011 10.5194/sed-3-975-2011 http://www.solid-earth-discuss.net/3/975/2011/ http://www.solid-earth-discuss.net/3/975/2011/sed-3-975-2011.html http://www.solid-earth-discuss.net/3/975/2011/sed-3-975-2011.pdf 975 999 2011-12-01 Floating sandstones off El Hierro (Canary Islands, Spain): the peculiar case of the October 2011 eruption V. R. Troll valentin.troll@geo.uu.se A. Klügel M.-A. Longpré S. Burchardt F. M. Deegan J. C. Carracedo S. Wiesmaier U. Kueppers B. Dahren L. S. Blythe T. Hansteen C. Freda D. A. Budd E. M. Jolis E. Jonsson F. Meade S. Berg L. Mancini M. Polacci Dept. of Earth Sciences, CEMPEG, Uppsala University, Sweden Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy Institute of Geosciences, University of Bremen, Germany Dept. of Earth and Planetary Sciences, McGill University, Canada Dept. of Physics (Geology), GEOVOL, University of Las Palmas, Gran Canaria, Spain Dept. of Earth and Environmental Sciences, Ludwig-Maximilians Universität (LMU), Munich, Germany Leibniz-Institute for Oceanography, IFM-GEOMAR, Kiel, Germany Geological Survey of Sweden, Uppsala, Sweden School of Geographical and Earth Sciences, University of Glasgow, UK SYRMEP Group, Sincrotrone Trieste S.C.p.A, Basovizza, Trieste, Italy Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, 56124 Pisa, Italy The eruption that started off the south coast of El Hierro, Canary Islands, in October 2011 has emitted intriguing eruption products found floating in the sea. These specimens appeared as floating volcanic "bombs" that have in the meantime been termed "restingolites" (after the close-by village of La Restinga) and exhibit cores of white and porous pumice-like material. Currently the nature and origin of these "floating stones" is 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 collected and analysed the structure and composition of samples and compared the results to previous work on similar rocks found in the archipelago. Based on their high silica content, the lack of igneous trace element signatures, and the presence of remnant quartz crystals, jasper fragments and carbonate relicts, we conclude that "restingolites" are in fact xenoliths from pre-island sedimentary rocks that were picked up and heated by the ascending magma causing them to partially melt and vesiculate. They hence represent messengers from depth that help us to understand the interaction between ascending magma and crustal lithologies in 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 these "restingolites" does therefore not indicate the presence of an explosive high-silica magma that is involved in the ongoing eruption. Aparicio, A., Bustillo, M. A., Garcia, R., and Araña, V.: Metasedimentary xenoliths in the lavas of the Timanfaya eruption (1730-1736, Lanzarote, Canary Islands): metamorphism and contamination processes, Geol. Mag., 143, 181–193, 2006. Aparicio, A., Tassinari, C. C. G., Garcia, R., and Araña, V.: Sr and Nd isotope composition of the metamorphic, sedimentary and ultramafic xenoliths of Lanzarote (Canary Islands): Implications for magma sources, J. Volcanol. Geotherm. Res., 189, 143–150, 2010. Araña, V. and Ibarrola, E.: Rhyolitic pumice in the basaltic pyroclasts from the 1971 eruption of Teneguía volcano, Canary Islands, Lithos 6, 273–278, 1973. Berg, S.: Constraining crustal volatile release in magmatic conduits by synchrotron X-ray μ-CT. Examensarbete vid Institutionen för geovetenskaper, Uppsala Universitet, ISSN 1650-6553, Nr 225, 2011. Carracedo, J. C., Rodríguez Badiola, E., Guillou, H., De La Nuez, J., and Pérez Torrado, F. J.: Geology and volcanology of La Palma and el Hierro, Western Canaries, Estudios Geológicos, 57, 1–124, 2001. Coello, J. J.: Sobre el origen de la 'restingolita', Actualidad Volcánica de Canarias- Noticias, 10 Oct 2011, http://www.avcan.org/?m=Noticias&N=911, 2011. Collier, J. S. and Watts, A. B.: Lithospheric response to volcanic loading by the Canary Islands: constraints from seismic reflection data in their flexural moat, Geophys. J. Int., 147, 660–676, 2001. Criado, C. and Dorta, P.: An unusual `blood rain' over the Canary Islands (Spain) The storm of January 1999, J. Arid. Environ., 55, 765–783, 1999. Gee, M. J. R., Masson, D. G., Watts, A. B., and Allen, P. A.: The Saharan debris flow: an insight into the mechanism of long runout submarine debris flows, Sedimentology 46, 317–335, 1999. Gimeno, D.: Informe realizado para el Ayuntamiento de El Pinar, El Hierro, Islas Canarias, sobre un piroclasto de la erupción en curso, Internal report, 10 Oct 2011. Guillou, H., Carracedo, J. C., Pérez Torrado, F. J., and Rodríguez Badiola, E.: K-Ar ages and magnetic stratigraphy of a hotspot-induced, fast grown oceanic island: El Hierro, Canary Islands, J. Volcanol. Geotherm. Res., 73, 141–155, 1996. Hammer, J. E., Cashman, K. V., Hoblitt, R. P., and Newman, S.: Degassing and microlite crystallization during pre-climactic events of the 1991 eruption of Mt Pinatubo, Philippines. Bull. Volcanol., 60, 355–380, 1999. Hansteen, T. H. and Troll, V. R.: Oxygen isotope composition of xenoliths from the oceanic crust and volcanic edifice beneath Gran Canaria (Canary Islands): consequences for crustal contamination of ascending magmas, Chem. Geol., 193, 181–193, 2003. Hansteen, T. H., Klügel, A., and Schmincke, H.: Multi-stage magma ascent beneath the Canary Islands: evidence from fluid inclusions, Contrib. Mineral. Petrol., 132, 48–64, 1998. Hoernle, K. A.: Geochemistry of Jurassic ocean crust beneath Gran Canaria (Canary Islands): implications for crustal recycling and assimilation, J. Petrol., 39, 859–880, 1998. IGN; Instituto Geográfico Nacional, Ministerio de Fomento, Servicio de Información Sísmica http://www.ign.es/ign/resources/volcanologia/HIERRO.html, 2011. Klügel, A., Schmincke, H.-U., White, J. D. L., and Hoernle, K. A.: Chronology and volcanology of the 1949 multi-vent rift-zone eruption on la Palma (Canary Islands), J. Volcanol. Geotherm. Res., 94, 267–282, 1999. Krastel, S. and Schmincke, H.-U.: Crustal structure of northern Gran Canaria deduced from active seismic tomography, J. Volcanol. Geotherm. Res., 115, 153–177, 2002 McLeod, P. and Sparks, R. S. J.: The dynamics of xenolith assimilation, Contrib. Mineral. Petrol., 132, 21–33, 1998. Pellicer, J. M.: Estudio geoquímico del vulcanismo de la isla del Hierro, Archipiélago Canario, Estudios Geol., 35, 15–29, 1979. Perugini, D., Poli, G., Petrelli, M., De Campos C. P., and Dingwell, D. B.: Time-scales of recent Phlegrean Fields eruptions inferred from the application of a "diffusive fractionation" model of trace elements, Bull. Volcanol., 72, 431–447, 2010. Schmincke, H.-U. and Graf, G.: DECOS / OMEX II, Cruise No 43, METEOR-Berichte 20001, Univ Hamburg, 1–99, 2000. Sparks, R. S. J.: The dynamics of xenolith assimilation, Contrib. Mineral. Pet., 132, 21–33, 1998. Stillman, C. J., Bennell-Baker, M. J., Smewing, J. D., Fuster, J. M., Muñoz, M., and Sagredo, J.: Basal complex of Fuerteventura (Canary Islands) is an oceanic intrusive complex with rift-system affinities, Nature 257, 469–471, 1975. Sumita, M. and Schmincke, H.-U.: Tephra event stratigraphy and emplacement of volcaniclastic sediments, Mogán and Fataga stratigraphic intervals, Part I: mineral and chemical stratigraphy of volcaniclastic units and correlation to the subaerial record, in: Proc. ODP, Sci. Results, 157, edited by: Weaver, P. P. E., Schmincke, H.-U., Firth, J. V., and Duffield, W., College Station, TX (Ocean Drilling Program), 219–266, http://dx.doi.org/10.2973/odp.proc.sr.157.114.1998doi:10.2973/odp.proc.sr.157.114.1998, 1998. Troll, V. R. and Schmincke, H.-U.: Magma mixing and crustal recycling recorded in ternary feldspar from compositionally zoned peralkaline ignimbrite "A", Gran Canaria, Canary Islands, J. Pet. 43, 243–270, 2002. Wiesmaier, S.: Magmatic differentiation and bimodality in oceanic island settings – implications for the petrogenesis of magma in Tenerife, Spain, PhD thesis, University of Dublin, Trinity College, 2010. Wolff, J. A. and Palacz, Z. A.: Lead isotope and trace element variation in Tenerife pumices: evidence for recycling within an ocean island volcano, Mineral. Mag., 53, 519–525, 1989. Ye, S., Canales, J. P., Rhim, R., Danobeitia, J. J., and Gallart, J.: A crustal transect through the northern and northeastern part of the volcanic edifice of Gran Canaria, Canary Islands, J. Geodyn., 28, 3–26, 1999.