阿武隈変成帯の"越代ダイアフトライト岩体"の変成交代収斂現象 : 越代-高帽山-大雄院構造帯の研究(その4)

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The diaphthoresis concept" speculated by Sugi (1933, 1938) in the Abukuma terrain, Japan, has attracted the interests of many geologists for a long time. However, it is rather difficult to note that most of their works on it could really materialize his concept. In 1978, the present authors found and described the diaphthorite (Takaboyama diaphthorite mass) in the Koshidai-Takaboyama-Daioh-in Structural Belt (Abbrev. K-T-D SB). Ever since, the diaphthorite problem in question has been shed light on in detail. The "Koshidai diaphthorite mass" in question, located in 25 km north of the abovementioned "Takaboyama diaphthorite mass" is distributed along the K-T-D SB as well and occupies an extent of about 10km in length and 0.5 to 1km in width. The mass is petrogenetically divided into six rock facies, viz. (1) porphyrolastic quartzose gneiss, (2) andalusite porphyroblast-bearing porphyroclastic biotite gneiss, (3) gabbro-amphibolite, (4) blastomylonitic biotite gneiss to schist, (5) chlorite schist and (6) tremolite-cummingtonite-anthophyllite schist. The pre-existing metamorphics, prior to the diaphthoresis superimposed to the mass, are originally estimated to be high-grade quartzose gneiss and biotite gneiss of the "Takanuki Series". As tabulated in Table 2, the questioned diaphthoresis is characterized by metamorphic degradation (Kata-, Meso- to Epi-zone), rock facies deterioration (S1〜S6), textural degradation (granoblastic to extremely lepidoblastic texture) and petrochemical change (basification): decrement for SiO_2, increment-decrement for Al_2O_3, Na_2O and K_2O, increment for Fe_2O_3, FeO, MgO and CaO. It is conclusively emphasized that the above-mentioned "metamorphic-metasomatic Convergence" owing to diaphthoresis had happened before thrusting up along the "Koshidai Thrust Zone" to Obergebirge ("Ishizumi and Saibachi zones" of the "Gozaisyo Series") as an allochthonous septa.
地学団体研究会の論文
1989-09-25

阿武隈変成帯の"越代ダイアフトライト岩体"の変成交代収斂現象 : 越代-高帽山-大雄院構造帯の研究(その4)

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