Experimental phase equilibria constraints on pre-eruptive storage conditions of the Soufreiere Hills magma

Barclay, J. ORCID: https://orcid.org/0000-0002-6122-197X, Carroll, M. R., Rutherford, M. J., Murphy, M. D., Devine, J. D., Gardner, J. and Sparks, R. S. (1998) Experimental phase equilibria constraints on pre-eruptive storage conditions of the Soufreiere Hills magma. Geophysical Research Letters, 25 (18). pp. 3437-3440. ISSN 1944-8007

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Abstract

New experimental results are used to constrain the P, T, X(H2O) conditions of the Soufriere Hills magma prior to ascent and eruption. The experiments were performed on a powdered andesite erupted in January, 1996, at an fO2 corresponding to ∼NNO+1 with PH2O and temperatures in the range 50 to 200 MPa and 800 to 940°C. Amphibole is stable at PH2O >115 MPa and temperatures <875°C. Quartz only becomes stable at low temperatures and after high degrees of crystallization (T <840°C, >72 wt% SiO2 in residual melt) at PH2O >115 MPa. Analyses of rhyolitic glass inclusions in quartz and plagioclase from recently erupted samples indicate melt water contents of 4.27±0.54 wt% H2O and CO2 contents <60 ppm. The evolved Soufriere Hills magma would therefore be H2O-saturated at pressures <130 MPa. These results suggest that the Soufriere Hills magma containing the stable assemblage amphibole, quartz, plagioclase, orthopyroxene, magnetite and ilmenite was stored at PH2O of 115-130 MPa, equivalent to a minimum depth for a water-saturated magma chamber of 5–6 km depth. Magma temperatures were initially low (820–840°C). Quartz is believed to have been destabilised by a heating event involving injection of new basaltic magma. The stability field of hornblende provides a useful upper limit (∼880°C) for the extent of this reheating.

Item Type:	Article
Faculty \ School:	Faculty of Science > School of Environmental Sciences
UEA Research Groups:	Faculty of Science > Research Groups > Geosciences Faculty of Science > Research Groups > Volcanoes@UEA (former - to 2018) Faculty of Science > Research Groups > Geosciences and Natural Hazards (former - to 2017)
Depositing User:	Rachel Snow
Date Deposited:	28 Mar 2011 10:47
Last Modified:	24 Jul 2024 08:41
URI:	https://ueaeprints.uea.ac.uk/id/eprint/27297
DOI:	10.1029/98GL00856

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