[Holtz] Pre-eruptive conditions prior to and after magma mixing at Unzen volcano: constraints from high pressure experimental investigations

German Title: Pre-eruptive conditions prior to and after magma mixing at Unzen volcano: constraints from high pressure experimental investigations

Abbreviation: 183

Current Status: completed

Main Applicant:Prof. Dr. Francois Holtz

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Year: 2004


The 1991-1995 eruption of Unzen is initiated by a mixing event (as observed in many eruptive systems) between a low-temperature phenocryst-rich dacitic magma and a high temperature andesitic magma Thus, understanding pre-eruptive conditions requires to determine pre-mixing conditions (in the two end-member magmas) and post-mixing conditions, and to model the processes occurring during mixing and ascent. In Unzen volcano, only post-mixing conditions in the magma chamber are well-characterized. The proposed project should contribute to provide new constraints on the pre-mixing magmas, especially the high temperature end-member, (including volatile contents, melt and phenocryst compositions) and on processes occurring during mixing and magma ascent. These constraints will be obtained from high pressure - high temperature experimental investigations on phase relations and volatile solubilities in silicate melts. The comparison of natural samples from the volcanic dome (including andesitic enclaves) and from the ICDP-drilling with experimental results will be used to understand the role of mixing (and possible subsequent degassing) on magma forcing and the role of kinetic processes during magma ascent (degassing, crystallization in a dynamic system).

Related Publications

Botcharnikov, Roman E., Holtz, Francois, Almeev, Renat R., Sato, Hiroaki, Behrens, Harald (2008). "Storage conditions and evolution of andesitic magma prior to the 1991–95 eruption of Unzen volcano: Constraints from natural samples and phase equilibria experiments" Journal of Volcanology and Geothermal Research 175 p168-180

Botcharnikov, Roman E, Holtz, Francois, Behrens, Harald (2007). "The effect of CO2 on the solubility of H2O-Cl fluids in andesitic melt" European Journal of Mineralogy 19 p671-680

Botcharnikov, R. E., Behrens, H., Holtz, F. (2006). "Solubility and speciation of C–O–H fluids in andesitic melt at T = 1100–1300 °C and P = 200 and 500 MPa" Chemical Geology 229 p125-143

Sato, Hiroaki, Holtz, Francois, Behrens, Harald, Botcharnikov, Roman, Nakada, Setsuya (2005). "Experimental Petrology of the 1991–1995 Unzen Dacite, Japan. Part II: Cl/OH Partitioning between Hornblende and Melt and its Implications for the Origin of Oscillatory Zoning of Hornblende Phenocrysts" Journal of Petrology 46 (2) p339-354

Holtz, Francois, Sato, Hiroaki, Lewis, Jared, Behrens, Harald, Nakada, Setsuya (2005). "Experimental petrology of the 1991–1995 Unzen dacite, Japan. Part I: phase relations, phase composition and pre-eruptive conditions" Journal of Petrology 46 (2) p319-337