Japan Geoscience Union Meeting 2014

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Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG61_2AM2] Petrology, Mineralogy and Resource Geology

Fri. May 2, 2014 11:00 AM - 12:45 PM 311 (3F)

Convener:*Toshiaki Tsunogae(Faculty of Life and Environmental Sciences (Earth Evolution Sciences), University of Tsukuba), Koichiro Fujinaga(Department of Systems Innovation, School of Engineering, University of Tokyo), Akira Miyake(Department of Geology and Mineralogy, Graduate School of Science, Kyoto University), Nobutaka Tsuchiya(Department of Geology, Faculty of Education, Iwate University), Chair:Koichiro Fujinaga(Department of Systems Innovation, School of Engineering, University of Tokyo), Akira Miyake(Department of Geology and Mineralogy, Graduate School of Science, Kyoto University)

11:00 AM - 11:15 AM

[SCG61-08] Al/Si disordered anorthite in anorthite megacryst from Miyake-jima: effect of non-stoichiometry on Al/Si distribution

*Takuya ECHIGO1, Mihoko HOSHINO2, Mitsuyoshi KIMATA3, Masahiro SHIMIZU3, Tomoaki MATSUI4, Norimasa NISHIDA5 (1.Faculty of Education, Shiga University, 2.Mineral Resources Research Group, AIST, 3.Earth Evolution Sciences, University of Tsukuba, 4.Faculty of Education, Kagoshiama University, 5.Research Facility Center for Science and Technology, University of Tsukuba)

Keywords:Anorthite, Al/Si order-disorder, Anorthite megacryst, Structual heterogeneity

The crystal chemistry of anorthite with the low content of albite (An92.0Ab3.4), part of a rapid cooled, anorthite megacryst occurring in 1940 ejecta from Miyake-jima volcano, Japan, has been investigated using single-crystal X-ray diffractometer and electron microprobe analyzer with wavelength dispersive X-ray spectroscopy (EMPA-WDS). The structure was refined in space group P-1 and cell parameters, a = 8.182(6) Å, b = 12.883(4) Å, c = 7.092(4) Å, α = 93.19(4) ⁰, β = 115.91 (4)⁰, γ = 91.18 (4)⁰. The final weighted R-factor is 3.77 % for 1549 reflections. Averaged T-O distances are 1.681 Å for T1(0), 1.674 Å for T1(m), 1.677 Å for T2(0) and 1.680 Å for T2(m), indicating each Al occupancy of 0.501, 0.453, 0.472, and 0.496, respectively. These results suggest that the Al/Si-distribution in the tetrahedral framework is highly disordered (QOD = 0.06), which results in having the c-axis in half along that determined in Al/Si ordered anorthites (c ~ 14 Å).