抄録
日本海拡大前の日本列島とシホテアリン地域との接合状態の復元と, 中央構造線の後期白亜紀左横すべり変位量の推定とをもとに, 中央構造線-畑川構造線(双葉断層)-シホテアリン中央断層からなる一連の白亜紀後期左横すべり断層系による, 日本列島-シホテアリン地域の諸地質体の再配列過程の復元を行った.さらに, この復元をもとに, 黒瀬川断層帯-中央構造線の一部-棚倉構造線-パルチザンスク断層-シホテアリン中央断層の一部からなる, 白亜紀前期左横すべり断層系を認定し, この断層系による地質体再配列についても議論した.これらの断層系は, 低角に大陸側に傾斜する断層面をもつものであり, 西南日本外帯の三波川帯から黒瀬川帯にかけての範囲の地質構造や, 「古領家帯」の残存物とされているナップ群の存在は, これら断層系の活動による上盤・下盤の挙動や, 断層系とこれらにより変位させられた古期地質体群の位置関係から説明されうる.
Rearrangements of pre-Cretaceous geologic units of Japan and Sikhote-Alin were restored using (1) a pre-Miocene reconstruction model for the geologic continuity between Japan and Sikhote-Alin and (2) an estimation of the left-lateral displacement along the Median Tectonic Line (MTL). The first model allows us to recognize two landward-dipping left-lateral fault systems along the eastern margin of Asia. The relative uplift of the footwall of these fault systems in a transtensional tectonic setting are responsible for the major geologic structure of the Outer Zone of Southwest Japan.We propose that all the older (pre-Jurassic) geologic units in present-day Japan and Sikhote-Alin lay on the landward side of the Jurassic accretionary complex, before the movement of the older Kurosegawa Fault System (KFS) in Early Cretaceous (120 to 90 Ma) time. The movement of the KFS may have carried the older units of the Kurosegawa, Abukuma, Southern Kitakami and Sergeevka belts from the southern extension of the Hida Marginal, Sangun-Renge and Permian "Sangun" belts, although the amount of lateral displacement along the KFS is still uncertain. As a result, the allochthonous older units have occupied the footwall of the KFS on the oceanward side of the Jurassic accretionary complex.The lateral displacement along the younger MTL Fault System (MFS) in Late Cretaceous (90 to 65 Ma) time, estimated to be about 500 km, likely carried the Southern Kitakami Belt and the Sawadani Unit (Northern Chichibu Belt) from the southern extensions of the Abukuma and Akiyoshi + Suo belts, respectively. We suggest that the "Paleo-Ryoke Belt" did not originally exist in all areas along the MTL. The "remnants of the missing Paleo-Ryoke Belt", presently located near the junctions of the KFS and MFS, consist of klippen separated from the allochthonous older geologic units by the uplift of the Sambagawa metamorphic rocks during the movement of the MFS only near the above junctions.
