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Floating stones off El Hierro, Canary Islands: xenoliths of pre-island sedimentary origin in the early products of the October 2011 eruption
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
3Institute of Geosciences, University of Bremen, Germany.
Dept. of Earth and Planetary Sciences, McGill University, Canada.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
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2012 (English)In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 3, no 1, 97-110 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Copernicus Publications , 2012. Vol. 3, no 1, 97-110 p.
National Category
Geology Geochemistry
Identifiers
URN: urn:nbn:se:uu:diva-171483DOI: 10.5194/se-3-97-2012ISI: 000309884400008OAI: oai:DiVA.org:uu-171483DiVA: diva2:511079
Funder
Swedish Research Council
Note

Correction in Solid Earth. Vol. 3(2) p. 189. DOI: 10.5194/se-3-189-2012

Available from: 2012-03-19 Created: 2012-03-19 Last updated: 2017-05-03Bibliographically approved
In thesis
1. Understanding Crustal Volatiles: Provenance,  Processes and Implications
Open this publication in new window or tab >>Understanding Crustal Volatiles: Provenance,  Processes and Implications
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Knowledge of the provenance of crustal volatiles and the processes by which they are released is extremely important for the dynamics of magmatic systems. Presented here are the results of multiple investigations, which aim to understand magmatic volatile contamination from contrasting but complementary perspectives. The main methodologies used include He and C isotope values and CO2/3He ratios of volcanic gases and fluids; simulation of magma-carbonate interaction using high-pressure high-temperature experimental petrology; X-ray microtomography of vesiculated xenoliths and computer modeling.

Findings show that the contribution from upper crustal volatiles can be substantial, and is dependant on the upper crustal lithology on which a volcano lies, as well as the composition of the magma supplied. Carbonate dissolution in particular is strongly controlled by the viscosity of the host magma. The details of the breakdown of vesiculated xenoliths is complex but has wide reaching implications, ranging from the dissemination of crustally derived materials through a magma body to highlighting that crustal volatiles are largely unaccounted for in both individual volcano and global volatile budgets. In synthesizing the conclusions from each of the individual perspectives presented, I propose the contribution of volatiles from crustal sources to play a significant role in many geological systems. This volatile component should be taken into consideration in future research efforts.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 37 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 912
Keyword
crustal volatiles, helium, carbon, volcanic gases and fluids, xeno-pumice, magma-carbonate interaction, upper crustal contamination
National Category
Geochemistry Geology
Identifiers
urn:nbn:se:uu:diva-171486 (URN)978-91-554-8311-1 (ISBN)
Public defence
2012-05-04, Hambergsalen, Geocentrum, Villavägen 16, 752 36 Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2012-04-11 Created: 2012-03-19 Last updated: 2012-04-19
2. Silicic Magma Genesis in Basalt-dominated Oceanic Settings: Examples from Iceland and the Canary Islands
Open this publication in new window or tab >>Silicic Magma Genesis in Basalt-dominated Oceanic Settings: Examples from Iceland and the Canary Islands
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The origin of silicic magma in basalt-dominated oceanic settings is fundamental to our understanding of magmatic processes and formation of the earliest continental crust. Particularly significant is magma-crust interaction that can modify the composition of magma and the dynamics of volcanism. This thesis investigates silicic magma genesis on different scales in two ocean island settings. First, volcanic products from a series of voluminous Neogene silicic centres in northeast Iceland are investigated using rock and mineral geochemistry, U-Pb geochronology, and oxygen isotope analysis. Second, interfacial processes of magma-crust interaction are investigated using geochemistry and 3D X-ray computed microtomography on crustal xenoliths from the 2011-12 El Hierro eruption, Canary Islands.

The results from northeast Iceland constrain a rapid outburst of silicic magmatism driven by a flare of the Iceland plume and/or by formation of a new rift zone, causing large volume injection of basaltic magma into hydrated basaltic crust. This promoted crustal recycling by partial melting of the hydrothermally altered Icelandic crust, thereby producing mixed-origin silicic melt pockets that reflect the heterogeneous nature of the crustal protolith with respect to oxygen isotopes. In particular, a previously unrecognised high-δ18O end-member on Iceland was documented, which implies potentially complex multi-component assimilation histories for magmas ascending through the Icelandic crust. Common geochemical traits between Icelandic and Hadean zircon populations strengthen the concept of Iceland as an analogue for early Earth, implying that crustal recycling in emergent rifts was pivotal in generating Earth’s earliest continental silicic crust.

Crustal xenoliths from the El Hierro 2011-2012 eruption underline the role of partial melting and assimilation of pre-island sedimentary layers in the early shield-building phase of ocean islands. This phenomenon may contribute to the formation of evolved magmas, and importantly, the release of volatiles from the xenoliths may be sufficient to increase the volatile load of the magma and temporarily alter the character and intensity of an eruption.

This thesis sheds new light on the generation of silicic magma in basalt-dominated oceanic settings and emphasises the relevance of magma-crust interaction for magma evolution, silicic crust formation, and eruption style from early Earth to present.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 54 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1338
Keyword
Silicic magmatism, Iceland, magma-crust interaction, proto-continental crust, early Earth, zircon geochronology and geochemistry, oxygen isotopes, 2011-2012 El Hierro eruption, crustal xenoliths, 3D X-ray μ-CT, volatiles
National Category
Geochemistry Geology
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-272318 (URN)978-91-554-9454-4 (ISBN)
Public defence
2016-03-03, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2016-02-11 Created: 2016-01-13 Last updated: 2016-02-19

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