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Science 23 May 1997:
Vol. 276. no. 5316, pp. 1245 - 1248
DOI: 10.1126/science.276.5316.1245
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Reports

Silicon and Oxygen Self-Diffusivities in Silicate Liquids Measured to 15 Gigapascals and 2800 Kelvin

Brent T. Poe, * Paul F. McMillan, David C. Rubie, Sumit Chakraborty, Jeff Yarger, Jason Diefenbacher

Mass transport properties of silicate liquids exhibit complex behavior as a function of pressure, as the tetrahedral framework structure of the liquid shifts to a more compact arrangement of atoms. For highly polymerized aluminosilicate liquids, oxygen diffusivities pass through a maximum at pressures below 10 gigapascals, whereas up to 15 gigapascals diffusivities continue to increase for sodium tetrasilicate liquid. A diffusivity maximum indicates a change in the mechanism of formation of 5-coordinated silicon or aluminum in the liquid. In the case of aluminosilicate liquids, this mechanism is restricted to aluminum sites in the network, suggesting that not only degree of polymerization, but also the ratio of aluminum to aluminum plus silicon strongly influences the behavior of magmatic processes at depth.

B. T. Poe and D. C. Rubie, Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany.
P. F. McMillan, J. Yarger, J. Diefenbacher, Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287, USA.
S. Chakraborty, Mineralogisch-Petrographisches Institut, Universität Köln, D-50674 Köln, Germany.
*   To whom correspondence should be addressed. E -mail: Brent.Poe{at}uni-bayreuth.de

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