九州肥後帯水越層中の花崗岩礫のK-Ar年代(古領家帯と黒瀬川帯の構成要素と改変過程)  [in Japanese] K-Ar ages of the granitic clasts from the Mizukoshi Formation in the Higo Belt, western Kyushu(Geotectonic evolution of the Paleo-Ryoke and Kurosegawa Terranes)  [in Japanese]

九州西部, 肥後帯水越層中の花崗岩礫について, K-Ar年代とSr同位体比の測定が行われた.K-Ar角閃石年代は260±13Maで, その年代を用いて計算したSrIは0.7049,0.7050となる.鉱物組成と浅所貫入を特徴づける組織などの岩石学的特徴, 低いK_2O量, ペルム紀の年代値および低いSrIから, 水越層中の花崗岩礫は南部北上帯の薄衣花崗岩礫に対比することができる.また, 南部北上帯上部古生界に対比できる竜峰山変成岩類や, 年代と原岩構成から阿武隈帯竹貫変成岩に対比できる肥後変成岩などが存在する肥後帯は, 古領家帯そのものであるといえよう.

K-Ar ages and Sr isotopic ratios were determined for the granitic clasts from the Mizukoshi Formation in the Higo Belt, western Kyushu. A K-Ar hornblende age is 260±13Ma and initial Sr isotope ratio is calculated as 0.7049 and 0.7050. Petrographical characteristics, K-Ar age, chemical composition such as low K_2O content, low initial Sr isotope ratio all suggest that the granitic clasts from the Mizukoshi Formation are correlative to those in the Usuginu-type conglomerate in the South Kitakami Belt and Kurosegawa Belt in Kyushu. The constituents of the Higo Belt, such as upper Paleozoic Ryuhozan and Mizukoshi Formation correlative with the Upper Paleozoic of the South Kitakami Belt and Higo metamorphic rocks correlative with the Takanuki metamorphic rocks in the Abukuma Belt, suggest that the Higo Belt is included in the Paleo-Ryoke Belt. The geotectonic relationship between the Higo and Kurosegawa Belts where the Usuginu-type conglomerates are distributed must be solved in future.