岡山縣小田郡陶山村のホルンフェルス中の閃長岩質アプライトの成因
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概要
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Syenitic aplite patches are found in biotite-hornfels at Suyama-Mura, Oda-Gun, Okayama Prefecture (Fig., 1)., These aplitic patches are mainly composed of oligoclase and orthoclase of 0.,5-1mm in size, showing the granitic texture., It is a remarkable fact that quartz is lacking in them., The biotite-hornfels consists of biotite, quartz, oligoclase and orthoclase., The mean size of the felsic constituents is 0.,005-0.,01mm., The biotite-hornfels of the district are almost equal in their petrographic features, except near the contacts of granites and porphyries., Minute pools composed of oligoclase porphyroblasts and orthoclase granules are found in the biotite-hornfels(Fig., 3)., The genesis of the syenitic aplite patches is interpreted as follows., 1., Glomeroporphyroblastic aggregates of twinned oligoclase were formed in the biotite-hornfels of argillaceous rock origin., As the oligoclase porphyroblasts grew, the orthoclase granules were combined, forming xenoblastic crystals., Quartz was removed and finally the syenitic aplite patches were formed., 2., In the course of the process, soda was added, and silica, iron, and magnesia were subtracted., A part of the materials subtracted was fixed in quartz and epidote-chlorite-veinlets in the hornfels., 3., These metasomatic changes were set in after the bulk of biotite-hornfels had been formed., The extent of the metasomatic effect in the area was as regional as that of the pure thermal effect., The metasomatism had no direct relation to the distribution of granites and porphyries indicated on the map (Fig., 2).,
- 日本地質学会の論文
- 1949-02-20