Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Médard, E. Articles by Grove, T. L. Search for Related Content GeoRef GeoRef Citation

Oxygen fugacity, temperature reproducibility, and H₂O contents of nominally anhydrous piston-cylinder experiments using graphite capsules

¹ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, U.S.A.
² Institut für Mineralogie und Petrographie, ETH Zürich, Clausiusstrasse 25, CH-8092 Zürich, Switzerland
³ Bayerisches Geoinstitut, Universität Bayreuth, POB 101251, D-95440 Bayreuth, Germany

Correspondence: ^* E-mail: etienne.medard{at}erdw.ethz.ch

The Pt-graphite double-capsule technique is a very commonly used method in high-temperature, high-pressure experimental petrology, particularly for anhydrous experiments relevant to primitive basaltic magmas and mantle melting. We have performed a series of experiments that place better constraints on the range of oxygen fugacity imposed by this capsule material, on the Fe³⁺/Fe²⁺ ratios in experimentally produced melts and minerals, and on the temperature reproducibility in Pt-graphite capsules. Oxygen fugacity in our piston-cylinder experiments using Pt-graphite capsules is CCO-0.7 (IW+1.5, QFM-2.2) at 1.5 GPa and 1360 °C. Comparison with other estimates and thermodynamic calculations indicate that a value of CCO-0.8 ± 0.3 can be used as a first approximation at least over the P-T range relevant for MORB and OIB magma generation (0.5–3.0 GPa, 1100–1500 °C). Under those conditions, the amount of Fe³⁺ in silicate phases (pyroxenes, olivine, glass) and spinel is negligible (Fe³⁺/Fe < 0.05) and would not significantly affect thermodynamic properties. Significantly higher values of f_O2 cannot be achieved using Pt-graphite or graphite only capsules, but f_O2 can be tuned to lower values by using small pieces of PtFe alloys. The potential range of f_O2 that can be reached in graphite or Pt-graphite capsules is CCO to CCO-4. Temperature reproducibility in piston-cylinder experiments has been examined and can be as low as ±10 °C. Finally, unless capsules are dried overnight at 400 °C before the experiment, small amounts of H₂O are always present in nominally dry experiments. These small amounts of H₂O should not, however, significantly change phase relations.

Key Words: Experimental petrology • oxygen fugacity • piston-cylinder • graphite • phase equilibria • reproducibility • Mössbauer spectroscopy • pyroxenes

This article has been cited by other articles:

				G. Van Den Bleeken, O. Muntener, and P. Ulmer Reaction Processes between Tholeiitic Melt and Residual Peridotite in the Uppermost Mantle: an Experimental Study at 0{middle dot}8 GPa J. Petrology, January 13, 2010; (2010) egp066v1. [Abstract] [Full Text] [PDF]

				J. Filiberto and A. H. Treiman Martian magmas contained abundant chlorine, but little water Geology, December 1, 2009; 37(12): 1087 - 1090. [Abstract] [Full Text] [PDF]