薄衣型礫岩の堆積とその造構環境 : 中部ペルム系粗粒砕屑岩における砂岩組成と堆積相の解析(古領家帯と黒瀬川帯の構成要素と改変過程)  [in Japanese] The sedimentary system and the tectonic implication of the Usuginu-type conglomerate in the South Kitakami Terrane, northeast Japan : especially to the sandstone petrography and the sedimentary facies of the Middle Permian coarse clastic deposits(Geotectonic evolution of the Paleo-Ryoke and Kurosegawa Terranes)  [in Japanese]

南部北上帯各地の薄衣型礫岩の堆積システムの相互比較とその供給地について検討した.その結果, 薄衣型礫岩の堆積相は地域ごとに大きく異なり, 砂岩組成も明瞭な差異を有することが明らかとなった.そのため, それぞれの地域の堆積システムは相異なる環境で形成され, かつ後背地構成や供給水系を異にしていたと考えられる.また, 薄衣型礫岩に付随する砂岩は一般に火成弧を起源とすると考えられ, 中でも大洞層・薄衣礫岩は火山岩が卓越する後背地を持つが, 落合層では後背地が未開析の火成弧から開析された火成弧へ変化している.中部ペルム系の岩相層序や当時の堆積盆分布を考慮すると, 氷上花崗岩やその周辺を含めて, 礫岩の一時的集積地や起源となる地質体を南部北上帯内部には見いだすことはできない.また, 薄衣型礫岩の堆積は火成弧的な環境のもとでの基盤運動の活発化・後背地の上昇を反映し, 当時の南部北上帯が衝突境界などに位置していた可能性を示す.

The Usuginu-type conglomerate (UTC) which mainly contains resedimented conglomerates and associated turbidite occur in the Middle to Upper Permian sequence of the South Kitakami Terrane, northeast Japan. The comparative study of the sedimentary system and the sandstone composition was carried out.A sedimentological studies of the UTC in the several areas (eastern Ichinoseki, Ochiai and Daido districts) have revealed that the submarine channel and slope-type fan-delta models in the shelf to slope environments are appropriate for the depositional system of the UTC. The granitic pebbles in the UTC suggest the presence of Permian intrusive rocks in the hinterland. Additionally, the composition of the sandstone associated with the UTC is rich in acidic - intermediate volcanic rock fragments probably derived from the Permian arc and pre-Permian strata which consist of acidic volcanic and volcani-clastic rocks.The difference of sedimentary facies and clastic composition among the several areas seems to be caused by : (a) differences in feeding system : conglomeratic clastic material was not supplied by one large discharge system, but rather from several small ones; and (b) the synsedimentary block faulting affected to the juxtaposition of shallow marine bank and deep sea subsiding basin. The relationship between the thick sequence of UTC and the composition of the clastic material has been documented in rapid uplifting of the hinterland and related sediment accumulation in the discriminative subsiding basin.Considering the stratigraphy and the relationship among the each basin during Middle Permian time, the provenance and/or the temporal sedimentary budget such as deltaic deposits of the UTC are not found out in the South Kitakami Terrane even if around the Hikami Granites.