Hello, Pat:
I don't work in rhyolites, but here are two modest ideas:
I suppose you only have magnetite as an oxide phase, so you cannot
determine the oxygen fugacity of the rock following the equations of
Andersen & Lindsley. Nevertheless, if you have mica (biotite) coexisting
with K-feldspar and magnetite, you can estimate the oxygen fugacity
following Wones, D.R. & Eugster, H.P. (1965): Amer. Miner. 50: 1228-1272.
Another reference I know on the subject (although not specifically on
rhyolites) is: Carmichael, I.E.S. & Nicholls, J. (1967): Journal of
Geophysical Research 72(18):4665-4687. I think these authors consider that
in the majority of cases, the oxygen fugacities of igneous rocks are
comprised between the HM and the QFM buffers, but they give some
qualitative relations between alkalis, magma evolution and fO2.
Hope that will serve you.
Regards.
Cris
Cristina de Ignacio San José
Departamento de Petrología y Geoquímica
Facultad de Geología
Ciudad Universitaria s/n
28040 Madrid
Spain
e-mail: [log in to unmask]
At 12:34 03/12/99 +0000, you wrote:
>Hi,
>Are there any igneous types out there who can help? I am using the TRACE3
>modelling program and I'm not sure what kind of oxygen fugacities would be
>suitable for a rhyolite system.
>Many thanks,
>Pat
>__________________
>Pat Thompson
>Geology Department
>University of Leicester
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