TY - JOUR

T1 - Storage conditions of Bezymianny Volcano parental magmas

T2 - Results of phase equilibria experiments at 100 and 700 MPa

AU - Almeev, Renat R.

AU - Holtz, Francois

AU - Ariskin, Alexei A.

AU - Kimura, Jun Ichi

N1 - Funding Information: Acknowledgments We thank Otto Dietrich for preparing the thin sections and Oliver Beermann, Parveen Fuchs, and Tatiana Shishkina for the help with capsule preparation and experiments. We thank Maxim Portnyagin for providing unpublished tephra glass compositions. Thoughtful and insightful reviews by D. Blatter and 3 anonymous reviewers significantly improved the clarity of the paper. The editorial work of Candace O’Connor, Pavel Izbekov and Timothy Grove is greatly appreciated. This work was supported by a DFG Grant (HO 1337/21). Copyright: Copyright 2013 Elsevier B.V., All rights reserved.

PY - 2013/11

Y1 - 2013/11

N2 - The crystallization sequence of a basaltic andesite from Bezymianny Volcano, Kamchatka, Russia, was simulated experimentally at 100 and 700 MPa at various water activities (aH2O) to investigate the compositional evolution of residual liquids. The temperature (T) range of the experiments was 950-1,150 °C, aH2O varied between 0.1 and 1, and the log of oxygen fugacity (fO2) varied between quartz-fayalite-magnetite (QFM) and QFM + 4.1. The comparison of the experimentally produced liquids and natural samples was used to constrain the pressure (P)-T-aH2O-fO2 conditions of the Bezymianny parental magma in the intra-crustal magma plumbing system. The phase equilibria constraints suggest that parental basaltic andesite magmas should contain ~2-2.5 wt% H2O; they can be stored in upper crustal levels at a depth of ~15 km, and at this depth they start to crystallize at ~1,110 °C. The subsequent chemical evolution of this parental magma most probably proceeded as decompressional crystallization occurred during magma ascent. The final depths at which crystallization products accumulated prior to eruption are not well constrained experimentally but should not be shallower than 3-4 km because amphibole is present in natural magmas (>150 MPa). Thus, the major volume of Bezymianny andesites was produced in a mid-crustal magma chamber as a result of decompressional crystallization of parental basaltic andesites, accompanied by mixing with silicic products from the earlier stages of magma fractionation. In addition, these processes are complicated by the release of volatiles due to magma degassing, which occurs at various stages during magma ascent.

AB - The crystallization sequence of a basaltic andesite from Bezymianny Volcano, Kamchatka, Russia, was simulated experimentally at 100 and 700 MPa at various water activities (aH2O) to investigate the compositional evolution of residual liquids. The temperature (T) range of the experiments was 950-1,150 °C, aH2O varied between 0.1 and 1, and the log of oxygen fugacity (fO2) varied between quartz-fayalite-magnetite (QFM) and QFM + 4.1. The comparison of the experimentally produced liquids and natural samples was used to constrain the pressure (P)-T-aH2O-fO2 conditions of the Bezymianny parental magma in the intra-crustal magma plumbing system. The phase equilibria constraints suggest that parental basaltic andesite magmas should contain ~2-2.5 wt% H2O; they can be stored in upper crustal levels at a depth of ~15 km, and at this depth they start to crystallize at ~1,110 °C. The subsequent chemical evolution of this parental magma most probably proceeded as decompressional crystallization occurred during magma ascent. The final depths at which crystallization products accumulated prior to eruption are not well constrained experimentally but should not be shallower than 3-4 km because amphibole is present in natural magmas (>150 MPa). Thus, the major volume of Bezymianny andesites was produced in a mid-crustal magma chamber as a result of decompressional crystallization of parental basaltic andesites, accompanied by mixing with silicic products from the earlier stages of magma fractionation. In addition, these processes are complicated by the release of volatiles due to magma degassing, which occurs at various stages during magma ascent.

KW - Bezymianny Volcano

KW - Crystallization experiments

KW - Magma storage

KW - Phase equilibria

UR - http://www.scopus.com/inward/record.url?scp=84885636201&partnerID=8YFLogxK

U2 - 10.1007/s00410-013-0934-x

DO - 10.1007/s00410-013-0934-x

M3 - Article

AN - SCOPUS:84885636201

VL - 166

SP - 1389

EP - 1414

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 5

ER -