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Iron and water losses from hydrous basalts contained in Au80Pd20 capsules at high pressure and temperature

Published online by Cambridge University Press:  05 July 2018

L. J. Hall
Affiliation:
Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
J. Brodie
Affiliation:
Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
B. J. Wood*
Affiliation:
Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
M. R. Carroll
Affiliation:
Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK

Abstract

We have performed experiments to determine the extents to which Fe and H2O are lost from hydrous basaltic melts contained in Au80Pd20 and graphite-lined Pt capsules at 0.7 –1 GPa and 1300–1350°C. All experiments were performed in the piston-cylinder apparatus. In order to minimize the possibility of rupture of the AuPd capsule and to control H2O loss we used a double-capsule method. The inner welded 2 mm diameter Au80Pd20 capsule was placed inside a welded 3 mm diameter Pt capsule, the intervening space being packed with hydrous sample. Loss of FeO* from the sample was found to be ≤4% relative in both the Au80Pd20 and graphite-lined Pt capsules in experiments of up to 24 h duration. Loss of H2O is greater and it depends on the oxidation state of the starting materials and the nature of the capsule. For starting mixes fired at 1 log fO2 unit above the quartz-fayalite-magnetite (QFM) buffer at 1 atm, H2O loss from Au80Pd20 capsules averaged 9% relative. Starting mixes fired at 1 log fO2 unit below the QFM buffer at 1atm lost, on average, 32% of their H2O when run in Au80Pd20 capsules at high pressure. All samples run in graphite-lined Pt capsules experienced dramatic H2O loss, averaging 52% relative, irrespective of initial oxidation state. We conclude that Au80Pd20 capsules are suitable for high-pressure hydrous melting experiments and that the sample loses very little Fe. In order to minimize H2O-loss, however, it is important that the starting materials be relatively oxidized.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2004

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Footnotes

**

Present address: Dipt. di Scienze della Terra, Università di Camerino, 62032 Camerino, Italy

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