Cryptoperthites in fayalite-hedenbergite trachyte from Oki-Dogo island, Japan

Three types of feldspar phenocrysts, mantled feldspars (anorthoclase cores and sanidine mantles), microperthitic feldspars and microscopically featureless sanidine are observed in a hand specimen of fayalite-hedenbergite trachyte from Oki-Dogo island in the Sea of Japan. Microscopically featureless sanidine phenocrysts of about Or46Ab49An5 were examined by X ray method and a transmission electron microscope. Diffuse streaks in X-ray diffraction patterns suggest the existence of coherent cryptoperthites. TEM observations confirmed cryptoperthitic textures in the sanidine phenocrysts. Two types of cryptoperthites are observed: finer tweed (about 2-4nm in periodicity) and coarser lamellar ones (around 8nm). The former is attributed to a spinodal decomposition. The latter may be slightly coarsened from the former.

[1]  S. Nakano.  Internal textures and chemical compositions of anti-rapakivi mantled feldspars from Oki-Dogo Island, Japan , 1992 .

[2]  中野 聰志.  Internal textures and chemical compositions of anti-rapakivi mantled feldspars from Oki-Dogo, Japan , 1992 .

[3]  K. Aoki,et al.  Temporal variations of Sr isotopic compositions for the rocks from Dogo, Oki islands, Shimane Prefecture , 1991 .

[4]  S. Nakano.  Behavior of alkali feldspar during hydrothermal alteration in the Koto Rhyolites, Southwest Japan , 1990 .

[5]  I. Parsons,et al.  Zoned ternary feldspars in the Klokken intrusion: exsolution microtextures and mechanisms , 1988 .

[6]  R. Yund,et al.  Thermal history of a Bishop Tuff section as determined from the width of cryptoperthite lamellae , 1985 .

[7]  H. Kurasawa.  Strontium isotopic ratios of the volcanic rocks from Dogo of the Oki Islands, Japan , 1984 .

[8]  I. Parsons,et al.  Feldspars and the Thermal History of Igneous Rocks , 1984 .

[9]  R. Yund,et al.  Thermal histories of two lava flows estimated from cryptoperthite lamellar spacings , 1980 .

[10]  G. Lofgren,et al.  Simultaneous crystallization of feldspar intergrowths from the melt , 1977 .

[11]  Gnnv E. LorcRnN.  Simultaneous crystallization of feldspar intergrowths from the melt , 1977 .

[12]  Y. Yusa.  A RAPID METHOD FOR QUANTITATIVE MICROPROBE ANALYSIS OF OLIVINES, PYROXENES AND FELDSPARS , 1975 .

[13]  M. Gandais,et al.  An electron-microscopic and X-ray study of complex exsolution textures in a cryptoperthitic alkali feldspar , 1973 .

[14]  M. Akizuki,et al.  The lamellar structure in moonstone and anorthoclase from Korea , 1970 .

[15]  J. Mcconnell.  Electron optical study of incipient exsolution and inversion phenomena in the system NaAlSi3O8-KAlSi3O8 , 1969 .

[16]  A. Albee,et al.  Empirical Correction Factors for the Electron Microanalysis of Silicates and Oxides , 1968, The Journal of Geology.

[17]  M. Uchimizu.  Geology and petrology of alkali rocks from Dogo, Oki Islands , 1966 .

[18]  T. Tomita.  Geology of Dôgo, Oki Islands, in the Japan Sea , 1936 .