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Earth’s surface consists of rigid 地球表面由持续移动并互相碰撞的 plates that are constantly shifting and 刚硬板块组成。 jostling one another. Plate movements 板块运动是地幔－地壳和地核之间 Line are the surface expressions of motions 的厚壳－运动的地表表现。 (5) in the mantle—the thick shell of rock that lies between Earth’s crust and its metallic core. Although the hot rock of 虽然地幔的炽热岩石是固体，在 the mantle is a solid, under the tre- 地壳及上层岩石的巨大压力下， mendous pressure of the crust and 它像粘性液体般流动。 (10) overlying rock of the mantle, it flows like a viscous liquid. The mantle’s motions, 地幔的运动就像在一锅开水里的 analogous to those in a pot of boiling 运动，把热的物质传到表面， water, cool the mantle by carrying hot 把冷的物质传到深处，从而冷却 material to the surface and returning 地幔。 (15) cooler material to the depths. When 当一块板块的边缘弯曲在另一块 the edge of one plate bends under 下面，它更冷的物质被地幔消耗， another and its cooler material is con- 熔岩从下面的板块升起并冲破覆盖 sumed in the mantle, volcanic activity 着的板块，火山运动就发生了。 occurs as molten lava rises from the (20) downgoing plate and erupts through the overlying one.地球板块运动及火山爆发产生 Most volcanoes occur at plate 大部分火山出现在板块边界。 boundaries. However, certain “mis- 但是，某些远离板块边缘的”错位” placed” volcanoes far from plate 火山来自第二种冷却地球深层内部 (25) edges result from a second, indepen- 的独立机制。 dent mechanism that cools the deep interior of Earth. Because of its prox- 因为接近地核，地幔基层的岩石 imity to Earth’s core, the rock at the 比上面的更热。 base of the mantle is much hotter than (30) rock in the upper mantle. The hotter the 地幔岩石越热，越要移动。 mantle rock is, the less it resists flow- ing. Reservoirs of this hot rock collect 炽热的岩石在地幔底部蓄集。 in the base of the mantle. When a 当积蓄足够大，一部分的热岩石 reservoir is sufficiently large, a sphere 用力顶破上面的地幔升向地表， (35)
of this hot rock forces its way up 在地形上形成一个广大的凸起。 through the upper mantle to Earth’s surface, creating a broad bulge in the topography. The “mantle plume” thus 形成的”地柱”一旦定型，就会继续 formed, once established, continues to 从地幔基层引导热的物质，直到 (40) channel hot material from the mantle 蓄池变空。 base until the reservoir is emptied. The surface mark of an established 一个定型的地柱的地表标志是一个 plume is a hot spot—an isolated 热点－一个孤立的火山区域，远离 region of volcanoes and uplifted terrain 表面板块边缘的凸起地形。 (45) located far from the edge of a surface plate. Because the source of a hot 由于热点来源是固定的，而地表 spot remains fixed while a surface 板块是移动的，过了一段长时间， plate moves over it, over a long period 一个活动的地柱造成一串火山或 of time an active plume creates a chain 火山岛，即地柱相对于移动板块 (50) of volcanoes or volcanic islands, a 的位置的线路标志。 track marking the position of the plume relative to the moving plate. The natural 夏威夷列岛的自然史清晰表明了 history of the Hawaiian island chain 太平洋板块在一个固定地柱上的 clearly shows the movement of the 移动。 Pacific plate over a fixed plume. 不在边缘火山爆发原因解释 现象解释 逻辑简图： 1P: earth consists of… mantle’s motion analogous to boiling water. One plates bends under another, volcanic activity… 2P: most occur at boundaries. However, certain occur far from edge result from……. The natural history of H shows…. | 
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发表于 2009-2-23 18:09:00
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