HR: 0800h
AN: V31A-1412 [Abstracts]
TI: Heat Capacity of Hollandite-Type KAlSi3O8 and Related Phase Equilibria
AU: * Yong, W
EM: wenjuny@umich.edu
AF: Wenjun Yong and Eric J.Essene, Dept. of Geological Sciences,
The University of Michigan, Ann Arbor, MI 48109
United States
AU: Dachs, E
EM: Edgar.Dachs@sbg.ac.at
AF: Edgar Dachs, Inst. Mineralogie,
Univ. Salzburg, Salzburg, 345020
Austria
AU: Tony, A C
EM: withe012@umn.edu
AF: Anthony C. Withers, Dept. of GEology and Geophysics, Univ. Minnesota, Minneapolis, MN 55455
United States
AU: Essene, E J
EM: essene@umich.edu
AF: Wenjun Yong and Eric J.Essene, Dept. of Geological Sciences,
The University of Michigan, Ann Arbor, MI 48109
United States
AB:
The behavior of potassium in the deep mantle is of great significance from geophysical and geochemical points of view.
Several experimental studies of phase transitions of stoichiometric KAlSi3O8 have been undertaken (Ringwood et al., 1967;
Liu, 1978; Kinomura et al., 1975; Yagi et al., 1994; Urakawa et al., 1994; Fasshauer et al., 1998; Akaogi et al., 2004).
Hollandite-type KAlSi3O8 is suggested to be a possible reservoir of potassium in the earth_s lower mantle. Tutti et al.
(2001) showed in experiments that hollandite-type KAlSi3O8 was a stable phase under the pressure of at least 2200 km deep in
the lower mantle and suggested that it is important host for potassium in that region. However, because of the lack of
low-temperature heat capacity data of hollandite-type KAlSi3O8, the Sa(298) is not well determined, hence the phase
equilibria related to hollandite-type KAlSi3O8 are still not well constrained in terms of slopes of the reactions.
In this study, we first synthesized hollandite-type KAlSi3O8 from sanidine glass as starting material at ca. 10 GPa and 1273K
using a multi-anvil device at the Univ. of Minnesota. The hollandite structure was confirmed by XRD analysis. The heat
capacity was measured in the range of 5-303 K using a PPMS at Salzburg. The low-temperature heat capacity data merge
smoothly with data measured on hollandite-type KAlSi3O8 between 160 and 700 K by Akaogi et al. (2004). The entropy of
hollandite-type KAlSi3O8 is calculated as 147.6 J/mol.K at 298.15 K. In combination with the existing thermodynamic and
experimental data, the phase boundary between hollandite-type KAlSi3O8 and wadeite, kyanite, and coesite is more accurately
fixed.
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 3630 Experimental mineralogy and petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting