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