...Therefore, it is possible that the continent that existed when the orthoquartzite layer was formed (probably in the late Precambrian era) later separated and moved as a microcontinental fragment (group), and reached the eastern edge of East Asia after the Cretaceous period, where it was incorporated as an allochthonous element into a part of the island arc system with island arc-type magmatism, and became a source of clastic material. In addition, the existence of the Oyashio paleocontinent from the Paleogene period, which contrasts with the Kuroshio paleocontinent in southwestern Japan, has been proposed based on deep-sea drilling data in the current forearc region between northeastern Japan and the Japan Trench (Huene, Nasu Noriyuki, et al., 1978). [Ichikawa Koichiro]... From [Japan Trench]…The subduction rate in the Japan Trench is estimated at about 8 cm per year. In late 1977, drilling by the Glomar Challenger uncovered a layer on the landward slope of the Japan Trench (about 120 km off the coast of Kuji) that showed evidence of being above sea level until the end of the Oligocene (23 million years ago), and it was named the Oyashio Paleocontinent. Today, this surface has sunk 2,600 m below sea level, and a layer of sediments about 1,000 m thick has formed a deep-sea flat surface. … *Some of the terminology used to refer to the "Oyashio Ancient Land" is listed below. Source | Heibonsha World Encyclopedia 2nd Edition | Information |
…そこで,オーソコーツァイト層形成当時(おそらく先カンブリア時代後期と推定されている)に存した大陸も,後にその一部分が微大陸片(群)として分離・移動し,白亜紀以降には東アジア東縁に到達し,島弧型火成活動を伴う島弧系の一部に,異地性要素としてくりこまれ,砕屑物供給源となったとも考えうる。なお,西南日本の黒潮古陸と対照するような,古第三紀当時の親潮古陸の存在が東北日本と日本海溝との間の現在の前弧域で深海掘削のデータから提唱されている(ヒューネ,奈須紀幸ら,1978)。【市川 浩一郎】。… 【日本海溝】より…日本海溝における沈み込み速度は約8cm/年と見積もられている。 1977年末のグローマー・チャレンジャー号による掘削によって,日本海溝の陸側斜面(久慈沖約120km)に,漸新世末(2300万年前)まで海面上に顔を出していた証拠をもつ地層が見いだされ,親潮古陸と名付けられた。現在ではこの表面は海面下2600mまで沈降し,その上に厚さ約1000mの堆積物をのせて深海平たん面をつくっている。… ※「親潮古陸」について言及している用語解説の一部を掲載しています。 出典|株式会社平凡社世界大百科事典 第2版について | 情報 |
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