Magma mixing during the 2010 Eyjafjallajökull eruption

• Main Authors: Portnyagin, Maxim, Borisova, A. Y., Plechov, P., Shkurski, B., Stefansson, A.
• Format: Conference Object
• Language: unknown
• Published: 2011
• Subjects: Eyjafjallajökull
• Online Access: https://oceanrep.geomar.de/id/eprint/13408/; http://agu-fm11.abstractcentral.com/s1aplanner/com.scholarone.s1aplanner.s1aplanner/S1APlanner.html?&CONFIG_ID=2224&USER_ID=1593989&ROLE_ID=11362&ROLE_TYPE_ID=10&PERSON2ROLE_ID=15483859&WORKFLOW_ID=17&CURRENT_PAGE=BROWSE_THE_PROGRAM&ALLOW_EDIT_INSTRUCTION

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 ...