Zincian hercynite from the Ryoke Zone in the Seto Inland Sea area Zincian hercynite-bearing pelitic gneiss is found from the Ryoke Zone of the Seto In

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1 Zincian hercynite from the Ryoke Zone in the Seto Inland Sea area Zincian hercynite-bearing pelitic gneiss is found from the Ryoke Zone of the Seto Inland Sea area, southwest Japan. The rock has the mineral association of biotite, muscovite, hercynite, sillimanite, plagioclase, quartz, graphite, ilmenite, tourmaline and apatite. Andalusite, cordierite and K-feldspar are sometimes associated with the above paragenesis. The hercynite is always included in the porphyroblastic sillimanite and shows the chemical composition of He62.7 `73.6Ga13.5 `25.4Sp11.9 `,3.1. Based on the microscopic texture and chemistry of hercynite and sillimanite, it has been inferred that the hercynite is recrystallized at the climax of the regional metamorphism at the expense of staurolhte. Fig. 1. Index map of the Uo-shima area. T, Takaigami-jima ; U, Uo-shima; E, Eno-shima.

2 Fig. 2. Geologic map and geologic profile of the Eno-shima showing the locality of sample containing zincian hercynite in the Uo-shima area, Southwest Japan. 1, tonalite; 2, psammitic gneiss; 3, pelitic gneiss; 4, siliceous gneiss; 5, basic gneiss; 6, fault; 7, strike-dip; 8, locality of zincian hercynite bearing rock.

3 Table 1. Chemical compositions of zincian hercynites (sample No. N80"4-1) Fig. 3. Photomicrograph taken without nicol and sketch of zincian hercynite (stipple) en closed in sillimanite porphyroblast (line) in pelitic gneiss from Eno-shima. Scale bar is 0.2 millimeter. sil, sillimanite; her, zincian hercynite. * Total Fe as FeO (Analyst: M. Suzuki)

4 Fig. 4. Electron microprobe profiles for Fe2O3 across two hercynite-bearing sillimanites in pelitic gneiss.

Richardson, S. W. (1968), Staurolite stability in a part of the system Fe-Al-Si-O-H. J. Petrol., 9, 467-488. Seo, T. and Hara, I.

5 Richardson, S. W. (1968), Staurolite stability in a part of the system Fe-Al-Si-O-H. J. Petrol., 9, Seo, T. and Hara, I. (1980), The development of schistosity in biotite schists from southwestern part of Mikawa Plateau, Central Japan. J. Geol. Soc. Japan, 86, Asami, M. and Hoshino, M. (1980), Staurolite bearing schists from the Hongu-san area in the Ryoke metamorphic belt, central Japan. J. Geol. Soc. Japan, 86, Atkin, B.P. (1978), Hercynite as a breakdown product of staurolite from within the aureole of the Ardara Pluton, Co. Donegal, Eire. Min eral. Mag., 42, Burns, R. C. (1970), Mineralogical applications of crystal field theory. pp University Press, Cambridge, England. Dietvorst, E. J. L. (1980), Biotite breakdown and the formation of gahnite in metamorphic rocks from Kemio, Southwest Finland. Contrib. Mineral. Petrol., 75, Griffen, D. T. and Ribbe, P. H. (1973), The crystal chemistry of staurolite. Amer. J. Sci., 273-A, Kwak, T. A. P. (1974), Natural staurolite break down reactions at moderate to high pressure. Contrib. Mineral. Petrol., 44, Loomis, T. P. (1972), Contact metamorphism of pelitic rocks by the Ronda ultramafic intrusion, southern Spain. Geol. Soc. Amer. Bull., 83, Seo, T., Yokoyama, S. and Hara, I. (1981), Metamorphism and tectonism of the Ryoke metamorphic belt. In Tectonics of paired metamorphic belts. Symposium Hiroshima 1980, Stoddard, E. F. (1979), Zinc-rich hercynite in high grade metamorphic rocks: a product of the dehydration of staurolite. Amer. Mineral., 64, Suzuki, M. and Osakabe. T. (1982), On the zincian spinel of the Hida Metamorphic Belt, central Japan. Mem. Geol. Soc. Japan, 21, Woodworth, G. J. (1979), Metamorphism, deforma tion and plutonism in the Mount Raleiph pend ant, Coast Mountains, British Columbia. Geol. Surv. Canada Bull., 295, 53 pp.

地質調査研究報告/Bulletin of the Geological Survey of Japan

地質調査研究報告/Bulletin of the Geological Survey of Japan Makoto Saito and Kazuhiro Miyazaki (2006) Jadeite-bearing metagabbro in serpentinite melange of the Kurosegawa Belt in Izumi Town, Yatsushiro City, Kumamoto Prefecture, central Kyushu. Bull. Geol. Surv.