日本列島の起源と付加型造山帯の成長 : リフト帯での誕生から都城型造山運動へ  [in Japanese] Origin and growth of accretionary orogen of the Japanese Islands : From birth at rift zone to Miyashiro-type orogeny  [in Japanese]

日本列島を含む東アジアの顕生代造山帯は, 海洋プレートの沈み込みによって先カンブリア時代の安定大陸の周囲に新しい大陸地殻が成長した場である。日本の起源は6〜7億年前に超大陸Rodiniaから揚子地塊がリフト化して離れた時の大陸縁に求められる。この受動的大陸縁は約5億年前に活動的大陸縁に転化した。新しい海洋プレート沈み込みは大陸縁に弧-海溝系を生じ, 4億年頃にそれが成熟すると, それ以後はほぼ水平な古生代-新生代付加体のナップ群やカルクアルカリ岩系火成岩をつくった。また間欠的な中央海嶺の海溝への沈み込みは, 低温高圧型変成帯の上昇や, 高温低圧型変成帯を伴う花崗岩バソリス帯の形成をもたらした。日本の造山帯は北米西岸のコルディレラ造山帯と鏡対称の構造をもち, それらの歴史は超海洋太平洋がたどったウィルソンサイクルの前半史にあたる。その後半史は2億年後に北米とアジアが衝突して次の超大陸Amasiaができる時に完結する。

The present Japanese Islands represent a segment of the Phanerozoic orogenic belt in East Asia where a Phanerozoic juvenile continental crust newly formed around the Precambrian cratons mainly by virtue of successive oceanic subduction from the Pacific side. The Japan segment of the continental margin first appeared during the 700-600 Ma rifting of the Yangtze (South China) craton from the Neoproterozoic supercontinent Rodinia. The Japan segment remained as a passive (Atlantic-type) continental margin until its tectonic conversion into an active (Pacific-type) margin around 500 Ma (Ordovician). The newly started oceanic subduction isolated a piece of the oldest oceanic crust connected to the pre-existing continental crust as a 580-520 Ma fore-arc ophiolite stigmatized by 450 Ma calc-alkaline signature. As the arc-trench system matured, continued subduction formed the oldest (ca. 450 Ma) set of high-P/T metamorphosed accretionary complex and calc-alkaline volcano-plutonics in Japan. This arc-trench system along the Yangtze craton fundamentally survived up to the present, leaving a subhorizontal nappe pile of the Paleozoic to Cenozoic accretionary complexes including their high-P/T metamorphic equivalents. Intermittent subduction of mid-oceanic ridge at the trench roughly in every 100 m.y. induced tectonic exhumation of a high-P/T metamorphic belt and formation of a granite batholith belt associated with low-P/T metamorphics. The orogenic edifice of Japan reflects a mirror image of that of the Cordilleran orogen in western North America (Laurentia), which corresponds to a conjugate rifted margin for Yangtze. The history of these orogens represents the earlier half of Wilson cycle of the super ocean called Pacific, and its later half will terminate when Laurentia collides with Asia in another 200 m.y. to form the next super continent Amasia. The 250 Ma collision between the Yangtze and Sino-Korean cratons and 20 Ma opening of Japan Sea left additional tectonic features in the modern island arc system of Japan.