A classification of the Earth's interior, the intermediate layer between the crust and the core. The part of the Earth between the Mohorovicic discontinuity, which is about 35 km deep under the continents and 5-10 km deep under the oceans, and the upper surface of the core, which is 2,900 km deep. Its volume accounts for 83% of the Earth's mass. It is composed of peridotite, whose main components are silicon, magnesium, and iron. Between 410 and 660 km deep, there is a layer where the speed of seismic waves increases rapidly, which corresponds to the change in the crystal structure of peridotite with pressure. This layer is called the transition zone, and the part shallower than this (which may include the transition zone) is called the upper mantle, and the part deeper than 660 km is called the lower mantle. The density of the top of the mantle is about 3.4 g/ cm3 , and increases with depth, reaching about 5.6 g/ cm3 at the bottom. The temperature is about 500°C at the top, increases with depth, and is estimated to be 4,000°C near the boundary with the core. Although the mantle is solid, it also has the property of flowing extremely slowly. The area up to a depth of about 100 km, including the crust, is called the lithosphere, which is difficult to flow, the rest of the upper mantle below that is called the asthenosphere, which is easy to flow, and the lower mantle below that is called the mesosphere, which is again difficult to flow. (→ Mantle convection) Mantle |
地球内部の分類の一つで,地殻と核との中間層。大陸の下では平均約 35km,海洋の下では 5~10kmの深さにあるモホロビチッチ不連続面と,深さ 2900kmにある核の上面の間の地球部分。体積は地球の 83%を占める。ケイ素,マグネシウム,鉄を主成分とする橄欖岩で構成される。深さ 410~660kmの間で地震波の速度が急激に増加する層があり,橄欖岩の結晶構造が圧力とともに変わることに対応している。この層を遷移層と呼び,これより浅い部分(遷移層を含めることもある)を上部マントル,660kmより深い部分を下部マントルという。マントル最上部の密度は 3.4g/cm3程度,深さとともに密度が大きくなり,最下部では 5.6g/cm3程度である。温度は最上部で 500℃程度,深さとともに高くなり,核との境界付近では 4000℃と推定されている。マントルは固体であるが,きわめてゆるやかに流れる性質も持ち合わせている。地殻を含めた深さ 100km程度まではリソスフェアと呼ばれる流れにくい領域で,その下にある上部マントルの残りの部分はアセノスフェアと呼ばれる流れやすい領域,さらにその下の下部マントルはメソスフェアと呼ばれ,再び流れにくい性質の領域になる。(→マントル対流)
マントル
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