High-pressure Raman scattering study of majorite-Garnet solid solutions in the system Mg4Si4O12-Mg3Al2Si3O12

M. H. Manghnani, V. Vijayakumar, J. D. Bass

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

We report here the results of Raman scattering measurements to 30 GPa on polycrystalline end-member Mj100 tetragonal majorite and two majorite-garnet solid solutions, Mj50Py50 and Mj50Py20 (where Mj = Mg4Si4O12 and Py = Mg3Al2Si3O12), synthesized at 17.7 GPa and 2000°C. The results are discussed in light of previous Raman, X ray, and elasticity studies. At ambient pressure, variations in the Raman spectra indicate changes in the structure and disorder with increasing Py content. For example, the spectra of Mj100 confirm its tetragonal structure, and the two bands in Mj100 at ~885 cm-1 and ~928 cm-1 merge in the case of Mj80Py20 and Mj50Py50- The spectra of Mj50Py50 and Mj80Py20 show similarity to those of Py100 (cubic garnet structure) and (Mg.79Fe.21)4Si4O12 majorite from the Catherwood meteorite, which also has cubic structure. The pressure dependencies of the Raman frequencies for all the modes are found to be linear, without discontinuities, throughout the pressure range of this study, implying no major structural changes. Using the pressure shift of the Raman bands, (∂vi/∂P), the mode Griineisen parameters, γi, are calculated using the bulk modulus values measured by Brillouin spectroscopy. The averaged values of mode γi for the three Mj-Py samples lie in the range 0.81-1.13, lower than those of pyrope garnet (1.5) but close to γth ~1.1 calculated for Mj58Py42.

Original languageEnglish (US)
Title of host publicationProperties of Earth and Planetary Materials at High Pressure and Temperature, 1998
EditorsMurli H. Manghnani, Takehiko Yagi
PublisherBlackwell Publishing Ltd.
Pages129-137
Number of pages9
ISBN (Electronic)9781118664421
ISBN (Print)9780875900834
DOIs
StatePublished - Jan 1 1997

Publication series

NameGeophysical Monograph Series
Volume101
ISSN (Print)0065-8448
ISSN (Electronic)2328-8779

ASJC Scopus subject areas

  • Geophysics

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    Manghnani, M. H., Vijayakumar, V., & Bass, J. D. (1997). High-pressure Raman scattering study of majorite-Garnet solid solutions in the system Mg4Si4O12-Mg3Al2Si3O12 In M. H. Manghnani, & T. Yagi (Eds.), Properties of Earth and Planetary Materials at High Pressure and Temperature, 1998 (pp. 129-137). (Geophysical Monograph Series; Vol. 101). Blackwell Publishing Ltd.. https://doi.org/10.1029/GM101p0129