HR: 09:00h
AN: MR11A-05    [Abstracts]
TI: Aluminum coordination and density of 4 and 5 component high-pressure aluminosilicate glasses
AU: * Allwardt, J R
EM: allwardt@pangea.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Dept. of GES, Bldg. 320, Stanford, CA 94305 United States
AU: Stebbins, J F
EM: stebbins@pangea.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Dept. of GES, Bldg. 320, Stanford, CA 94305 United States
AU: Du, L
EM: lsdu@pangea
AF: Department of Geological and Environmental Sciences, Stanford University, Dept. of GES, Bldg. 320, Stanford, CA 94305 United States
AU: Frost, D J
EM: Dan.Frost@uni-bayreuth.de
AF: Bayerisches Geoinstitut, UniversitAt Bayreuth, Bayerisches Geoinstitut UniversitAt Bayreuth, Bayreuth, D-95440 Germany
AU: Withers, A C
EM: withe012@tc.umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr SE, Minneapolis, MN 55455-0219 United States
AU: Hirschmann, M M
EM: Marc.M.Hirschmann-1@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr SE, Minneapolis, MN 55455-0219 United States
AB: The density and viscosity of silicate melts are strongly dependent on pressure and composition, owing in part to atomic-scale structural changes that occur at high pressure. In an attempt to further understand these changes, we have used Al-27 MAS NMR to determine the speciation of the aluminum cations and measured the density of glasses quenched from four and five component aluminosilicate melts in the pressure range of 2 to 8 GPa. Our previous work on ternary aluminosilicate glasses (Allwardt et al., 2005) established that high field strength (i.e., Ca) modifier cations induce more high-coordinated Al than lower field strength (i.e., Na and K) cations and the amount of high-coordinated Al gradually increases with increasing synthesis pressure to percentages as high as 81 % for the Ca-aluminosilicate glass at 10 GPa. Density determinations show that they are also up to 16 % more dense than the ambient pressure glass and that the density and the Al-coordination show a linear correlation. Quantification of spectra from the present study shows an increasing Al-coordination with increasing average field strength of modifier cation. These data also show that when multiple modifier cations are present (e.g. Ca and K), the Al coordination is lower than what would be expected due to linear mixing of the appropriate aluminosilicate endmembers. This experimental observation likely suggests that mixing of modifier cations in specific structural sites influences the formation of high coordinated Al in high-pressure glasses and melts.
DE: 3619 Magma genesis and partial melting (1037)
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005