Magma mixing during the 2010 Eyjafjallajökull eruption.

Portnyagin, Maxim, Borisova, A. Y., Plechov, P., Shkurski, B. and Stefansson, A. (2011) Magma mixing during the 2010 Eyjafjallajökull eruption. [Poster] In: AGU Fall Meeting 2011. , 05.-09.12.2011, San Francisco, USA .

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We performed detailed study of matrix glasses, olivines and melt inclusions in 6 samples of tephras of the 2010 Eyjafjallajökull eruption. Tephras erupted during the early basaltic stage (March 20 – April 13) are very homogeneous with respect to matrix glass compositions and host assemblage of primitive phenocrysts (olivine Fo75-87, Cr-spinel Cr# = 0.14 - 0.55). The olivines have normal or rhythmic zoning which suggests multiple episodes of mixing with more primitive magmas and crystallization before eruption. Glasses of the initial andesitic stage (April 14 - 30) fall into three groups: basaltic (group 2a, <10 %), andesitic (group 2b, >80% ) and dacitic (group 2c, <10%). Silicic 2c group glasses are very similar to those from the 1821 - 1823 tephra. The wide range of glass compositions suggests incomplete mixing of mafic and silicic magmas during the early eruption stage. Glasses from the late andesitic stage (May 1 - 22, group 3) have exclusively andesitic composition, slightly more primitive than on the early stage. The compositions of olivine cores and Cr-spinel inclusions in olivine in the late stage andesites are identical to those in basalts and suggest injection of basaltic magma into silicic magma shortly before eruption of andesite. The composition of shallow magma reservoir before the 2010 eruption could have composition similar to the group 2c glasses. A remarkable peculiarity of silicic Eyjafjallajökull glasses is high Cl (0.2-0.45 wt%) and high Cl/K2O (0.07-0.13) which are higher compared to basaltic glasses and primitive inclusions in olivine (Cl=0.02-0.09 wt%, Cl/K2O=0.04-0.09). The Cl enrichment in silicic Eyjafjallajökull melts may be an indicator of assimilation of crustal rocks altered via interaction with Cl-rich surface or oceanic waters.

To estimate the residence time of basaltic xenocrysts in andesitic magma erupted on May 11, we measured compositional profiles in olivine xenocrysts and calculated the time required to form such a zoning via Fe-Mg diffusion. Orientation of the studied olivine sections has been determined with universal table and verified by comparing the facet angles with the ideal olivine crystal shape. Our modeling indicates that the high-Mg olivine phenocrysts interacted with andesitic magma no longer than 3 - 15 days. This is consistent with increased seismic activity beneath the volcano during first days in May 2010 and indicates repeated intrusions of basaltic magma from depth into shallow silicic magma reservoir. These intrusions were likely the reason for the renewed explosive activity of Eyjafjallajökull in May 2010. Narrow range of volcanic glasses from tephra erupted on the May, 11 implies that complete mixing of silicic and basaltic melts had occurred within a few days.

Document Type: Conference or Workshop Item (Poster)
Keywords: Volcanology; Explosive volcanism; Geochemical modeling; Fluid and melt inclusion geochemistry; Magma chamber processes
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
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Date Deposited: 12 Jan 2012 10:42
Last Modified: 23 Feb 2012 06:18

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