Pre-eruptive conditions prior to and after magma mixing at Unzen volcano: constraints from high pressure experimental investigations
Final Report Abstract
New experimental constraints on the pre-eruptive conditions of 1991-1995 eruption at Unzen volcano were gained. This eruption was initiated by a mixing event between a low-temperature phenocryst-rich dacitic magma and a high-temperature nearly-aphyric andesitic magma. The project was focused on the conditions of the high temperature andesitic magmas, (including volatile contents, melt and phenocryst compositions) and on processes occurring during mixing and magma ascent. The pre-eruptive constraints were obtained from high pressure - high temperature experimental investigations of (1) phase relations in silicate melts, (2) volatile solubilities, (3) mixing processes between rhyodacitic and andesitic magmas and (4) decompression-induced vesiculation of Unzen groundmass composition. Finally, the investigation of natural samples from the volcanic dome and the comparison with experimental results were used to quantify temperature and volatile concentrations in the andesitic magma, to understand the role of mixing (and possible subsequent degassing) on magma forcing and the role of kinetic processes during magma ascent (degassing in a dynamic system).
Publications
- (2005) Experimental petrology of the 1991-1995 Dacite of Unzen volcano, 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, 339-354
Sato H., Holtz F., Behrens H., Botcharnikov R.E., Nakada, S.
- (2005) Experimental petrology of the 1991-1995 Unzen Dacite, Japan. Part I: phase relations, phase composition and preemptive conditions. Journal of Petrology, 46, 319-337
Holtz F., Sato H., Lewis J., Behrens H., Nakada S.
- (2005) Mixing properties and speciation in magmatic fluids: A significance for fluid-saturation conditions of magmas. 9th CCVG-IA VCEI, Italy
Botcharnikov, R.E., Holtz, F., Behrens, H., and Preise, M.
- (2005) Petrology of mafic inclusions in the 1991-1995 dacite of Unzen volcano. Unzen Workshop 2005, Unzen, Shimabara, Japan, 26-28.02.2005, O-17
Sato, H., Nakada, S., Holtz, F., Botcharnikov, R.E., and Behrens, H.
- (2005) Solubility of C-O-H mixtures in natural melts: new experimental data and application range of recent models. Annals of Geophysics, 48 (4-5), 633-646
Botcharnikov, R., Freise, M., Holtz, F., and Behrens, H.
- (2005) The effect of redox state on the solubility of C-O-H fluids in silicate melts: new experimental evidences. EGU meeting, Wien, Austria, EGU-05-A- 09237
Botcharnikov, R.E., Holtz, F., Behrens, H., and Freise, M.
- (2005) Volatiles as tracers for understanding mixing processes in Unzen magmas: constraints from experiments. Joint colloquium IODP-ICDP, Potsdam, Germany, 14-16.03.2005
Botcharnikov, R.E., Holtz, F., Behrens, H., and Sato, H.
- (2005) Volatiles as tracers for understanding mixing processes in Unzen magmas: constraints from experiments. Unzen Workshop 2005, Unzen, Shimabara, Japan, 26-28.02.2005, O-18
Holtz, F., Sato, H., Behrens, H., Botcharnikov, R.E., Vetere, F., and Nakada, S.
- (2006) Pre-eruptive conditions prior to and after magma mixing at Unzen volcano: constraints from high pressure experimental investigations. Proc. ICDP-IODP meeting, Greifswald, Germany, 35-36
Botcharnikov R.E., Holtz F., Behrens H., and Sato H.
- (2006) Solubility and speciation of C-O-H fluids in andesitic melt at T=l 100 - 1300°C and P=200 and 500 MPa. Chemical Geology, 229,125-143
Botcharnikov, R.E, Behrens, H., and Holtz, F.
- (2006) The effect of H2O on mixing between rhyolitic and andesitic magmas. Proc. EMPGX1, Bristol, England, 10
Botcharnikov R. E., Vetere F., Behrens H., and Holtz F.
- (2007) Changes in magmatic conditions on magma ascent during 1991-95 eruption of Unzen volcano, Japan as deduced from core and dome samples and high pressure experiments. Proc. ICDP-IODP meeting, Potsdam, Germany
Botcharnikov R.E., Holtz F., Behrens H., Cichy S., Dziony W., and Sato H.
- (2007) The effect of CO2 on the solubility of H2O-Cl fluids in andesitic melt. European Journal of Mineralogy, 19, 671-680
Botcharnikov, R.E, Holtz, F., and Behrens, H.
- (2008) Experimental constraints on the redox and compositional control of S solubility in hydrous felsic to mafic magmas. EGU meeting, Wien, Austria, EGU2008-A-10859
Botcharnikov, R.E., Wilke, M., Jugo, P.J., Holtz, F.
- (2008) The origin of S4+ detected in silicate glasses by XANES. American Mineralogist, 93, 235-240
Wilke, M., Jugo, P.J., Klimm, K., Susini, J., Botcharnikov, R., Kohn, S.C., Janousch, M.
