Ryoke metamorphic belt

Japanese: 領家変成帯 - りょうけへんせいたい

A regional metamorphic belt consisting mainly of gneiss that is distributed along the north side of the Median Tectonic Line. It is thought to have been formed by the Cretaceous orogeny related to the formation of the Japanese archipelago. It begins near Takato in Nagano Prefecture, and extends from the northern part of the Kii Peninsula through the Seto Inland Sea region to near Yatsushiro in Kumamoto Prefecture. Its eastern extension is cut by the Fossa Magna, but it is thought to include metamorphic rocks from the Tsukuba region of Ibaraki Prefecture to the Abukuma Highlands. The metamorphic rocks consist of various gneisses, including mica gneiss, sillimanite, and andalusite, and are thought to have been formed by high-temperature, low-pressure metamorphism of Paleozoic argillaceous rocks, sandstone, and chert. One of the characteristics of this metamorphic rock is that there are many granitic intrusions associated with the gneisses. There are two theories about the time of metamorphism: one is that it occurred at the end of the Paleozoic era, and the other is that it occurred from the Cretaceous period of the Mesozoic era to the Paleogene period of the Cenozoic era. However, absolute dating has revealed that it occurred 100 million years ago or 60 million years ago, and the latter is correct. The name comes from the place name Oku Ryoke in the upper reaches of the Tenryu River.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

中央構造線の北側に沿って分布する，片麻岩を主体とする広域変成帯。日本列島の形成に関係した白亜紀の造山運動によってできたものと考えられている。分布は長野県高遠付近に始まり，紀伊半島北部から瀬戸内海地域を通って熊本県八代付近に及ぶ。東方延長はフォッサ・マグナによって切られるが，茨城県筑波地方から阿武隈高地にかけての変成岩類もこれに含まれるとみられている。変成岩は，雲母片麻岩やケイ線石，紅柱石などを含む種々の片麻石からなり，古生界の泥質岩，砂岩，チャートなどが高温・低圧型の変成作用を受けてできたものと考えられる。片麻岩類に伴って花崗岩類の貫入岩体が多いのもこの変成岩の特徴の一つである。変成作用の時期については，古生代末という見解と，中生代の白亜紀から新生代の古第三紀にかけてという 2説があったが，絶対年代の測定では，1億年前あるいは 6000万年前で，後者が正しいことが明らかになった。なお名称は天竜川上流の地名奥領家に由来する。

出典　ブリタニカ国際大百科事典小項目事典ブリタニカ国際大百科事典小項目事典について　情報

<<: Hound - Ryoken

>>: Ryogenokan - Officials outside the government