Heterogeneous vesiculation of 2011 El Hierro xeno-pumice revealed by X-ray computed microtomography

• Published in: Bulletin of Volcanology
• Main Authors: Berg, Sylvia E., Troll, Valentin R., Deegan, Frances M., Burchardt, Steffi, Krumbholz, Michael, Mancini, Lucia, Polacci, Margherita, Carracedo, Juan Carlos, Soler, Vicente, Arzilli, Fabio, Brun, Francesco
• Format: Article in Journal/Newspaper
• Language: English
• Published: Uppsala universitet, Mineralogi, petrologi och tektonik 2016
• Subjects: El Hierro; Xeno-pumice; X-CT imaging; Vesicle morphologies; Vesicle size distribution; Heterogeneous vesiculation; Sedimentary ocean crust; Geology; Geologi; Iceland
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-272316; https://doi.org/10.1007/s00445-016-1080-x

During the first week of the 2011 El Hierro submarine eruption, abundant light-coloured pumiceous, high-silica volcanic bombs coated in dark basanite were found floating on the sea. The composition of the light-coloured frothy material ('xeno-pumice') is akin to that of sedimentary rocks from the region, but the textures resemble felsic magmatic pumice, leaving their exact mode of formation unclear. To help decipher their origin, we investigated representative El Hierro xeno-pumice samples using X-ray computed microtomography for their internal vesicle shapes, volumes, and bulk porosity, as well as for the spatial arrangement and size distributions of vesicles in three dimensions (3D). We find a wide range of vesicle morphologies, which are especially variable around small fragments of rock contained in the xeno-pumice samples. Notably, these rock fragments are almost exclusively of sedimentary origin, and we therefore interpret them as relicts an the original sedimentary ocean crust protolith(s). The irregular vesiculation textures observed probably resulted from pulsatory release of volatiles from multiple sources during xeno-pumice formation, most likely by successive release of pore water and mineral water during incremental heating and decompression of the sedimentary protoliths. The manuscript version of this article was used under the name "Heterogeneous vesiculation of 2011 El Hierro xeno-pumice revealed by synchrotron μ-CT" in the following thesis: Silicic Magma Genesis in Basalt-dominated Oceanic Settings: Examples from Iceland and the Canary Islands http://uu.diva-portal.org/smash/record.jsf?pid=diva2:893923