⑹外文翻译-

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxx本科毕业论文外文资料翻译系别：xxxxxxxxxxxxxx专业： xxxxxxxx姓名： xxxxxxxxxxx学号： xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx岩浆成因基于现有的科学证据显示，地球的地壳和地幔主要由坚硬的岩石组成。

另外，外核呈流体状态，这种材料是非常密集并保持在地球内部深处的。

那么，什么是产生地球上的火山活动的岩浆源？我们知道，岩浆在岩石被加热到其熔点时生成。

在近地表环境，花岗岩在800℃左右的温度下开始融化，而玄武岩必须达到1000℃以上。

一个重要的差异存在于单一物质和化合物之间，例如冰和几种不同的矿物混合成的火成岩的熔点。

冰融化在一定的温度下，而大部分火成岩在几百度的温度范围内熔融。

岩石被加热时，第一个形成液体的包含一个比原岩百分比高的低融点矿物。

如果继续熔化，该熔体将稳步接近从岩石的整体组成。

然而，大多数情况下，熔融是不完整的。

这个过程被称为部分熔融，不全部生成岩浆。

部分熔融的结果明显比母岩熔融产生的二氧化硅含量高。

回想一下，玄武质岩石具有较低的硅含量，花岗质岩石具有更高的硅含量。

因此，部分熔融产生的岩浆比他们从母岩形成更接近于花岗岩成分。

正如我们将看到的，这个想法将有助于我们了解全球分布的各种类型的火山活动。

岩石热的来源是什么？来源之一被认为是集中在上地幔和地壳的放射性元素衰变过程中释放的热量。

在地下矿井的工人很早就认识到温度随深度增加。

虽然增长率因地而异，它被认为是平均上升每公里增加20℃到30℃。

这种温度随着深度逐渐增加，称为地热梯度。

如果温度是决定岩石融化的唯一因素，地球将成为仅覆盖着薄薄一层固体外壳的熔融球。

然而，压力也随深度而增加。

由于岩石受热膨胀，为了克服围压的影响，岩石融化需要额外的热量。

在一般情况下，围压的增加会导致岩石的熔点提高。

影响岩石熔点的另一个重要因素是它的水含量。

归结到一点，水越多熔点越低。

水对降低熔点的效果被增加的压力放大。

因此，在同压力下“湿”岩石比具有相同成分“干”岩石的熔点低。

因此，除了岩石的组合物，温度，压力和水的含量确定岩石作为固体或液体存在。

在自然界中，岩石融化的原因有两个。

第一，加热到其熔点时岩石融化。

这可能发生，例如，当热地幔岩向表面迁移并接触到地壳岩石具有较低的熔点。

在该地区，包括黄石公园火山的活动导致这样的活动。

这里玄武质岩浆在地幔中形成的热运到地壳，那里的地壳岩石部分熔融产生的富硅岩浆。

第二，没有温度的增加，围压的降低可以降低熔融温度足以触发熔化。

每当发生岩石上升，从而移动到较低压力的区域。

这两个过程都被认为是在岩浆的形成中起重要的作用。

大多数的玄武质岩浆被认为起源于橄榄岩部分熔融的岩石，是上地幔的主要成分。

实验室研究证实，干燥，不富含二氧化硅的岩石部分熔融产生有玄武岩组成的岩浆。

因为在高的温度和压力环境下存在的地幔岩石，融化的结果往往是在围压的降低。

这可能发生，例如，其中地幔岩石作为一个缓慢移动的对流单元的一部分上升。

由于玄武质岩浆形成在地表以下几公里，我们可以预计，这些材料大部分将在到达表面冷却并结晶。

然而，由于干燥的玄武岩岩浆向上移动，围压的稳步减少，进一步降低了熔点。

玄武质岩浆出现快速上升足以使他们进入较冷的环境中的热损失的熔点下降所抵消。

因此，大爆发的玄武质岩浆是常见在地球表面。

相反，花岗质岩浆被认为是由富含水的岩石部分熔融进行温度升高产生。

作为一个潮湿的花岗质熔点上升，围压减小，从而减少水对降低熔融温度的影响。

此外，花岗质熔体比玄武质岩浆含二氧化硅更多和更粘。

因此，对比玄武质岩浆产生巨大的流出的熔岩，大多数花岗质岩浆在失去流动性之前到达地面，因此往往会产生较大的侵入特征如岩基。

在这些场合时，富硅岩浆到达地表，爆炸性的火山碎屑流，如那些产生的黄石高原。

尽管大多数岩浆被认为是部分熔融产生，一旦形成的岩浆体组合物可以随时间显著变化。

例如，作为岩浆体向上运移，它可能包含了一些周围的岩石。

由于围岩同化，岩浆的成分改变。

此外，回想起我们讨论鲍文反应系列，在凝固过程中，岩浆经常发生分离结晶。

这将产生一个完全不同于母体点岩浆。

考虑这些过程，至少部分地，即一个单一的火山可以具有宽范围的化学组成的拉伸性熔岩。

外文原文Origin of MagmaBased on available scientific evidence, the earth’s crust and mantle are composed primarily of solid rock. Further, although the outer core is in a fluid state, this material is very dense and remains deep within the earth. What then is the source of magma that produces the earth’s volcanic activity?We know that magma can be produced when rock is heated to its melting point. In a near-surface environment, rocks of granitic composition begin to melt at temperatures around 800℃，whereas basaltic rocks must reach temperatures above 1000℃ before melting will begin. One important difference exists between the melting of a substance that consists of a single compound, such as ice, and the melting of igneous rocks, which are mixtures of several different minerals. Whereas ice melts at a definite temperature,most igneous rocks melt over a temperature range of a few hundred degrees. As a rock is heated, the first liquid to form will contain a higher percentage of the low-melting-point minerals than does the original rock. Should melting continue, the composition of the melt will steadily approach the overall composition of the rock from which it is derived. Most often, however, melting is not complete. This process, known as partial melting, produces most, if not all, magma.A significant result of partial melting is the production of a melt with a higher silica content than the parent rock. Recall that basaltic rocks have a relatively low silica content and that granitic rocks have a much higher silica content. Consequently,magmas generated by partial melting are nearer the granitic end of the compositional spectrum than the parent material from which they formed. As we shall see, this idea will help us to understand the global distribution of the various types of volcanic activity.What is the heat source to melt rock? One source is the heat liberated during the decay of radioactive elements that are thought to be concentrated in the upper mantle and crust. Workers in underground mines have long recognized that temperatures increase with depth. Although the rate of increase varies from place to place, it is thought to average between 20℃and 30℃per kilometer in the upper crust. This gradual increase in temperature with depth is known as the geothermal gradient.If temperature were the only factor to determine whether or not a rock melts, the earth would be a molten ball covered with only a thin, solid outer shell. However, pressure also increases with depth. Since rock expands when heated, extra heat is needed to melt buried rocks, in order to overcome the effect of confining pressure. In general, an increase in the confining pressure causes an increa se in the rock’s melting point. Another important factor affecting the melting point of rock is its water content.Up to a point, the more water present, the lower the melting point. The effect of water on lowering the melting point is magnified by increase d pressure. Consequently, “wet”rock under pressure has a much lower melting temperature than “dry” rock of the same composition. Therefore, in addition to a rock’s composition, its temperature, confining pressure, and water content determine whether the rock exists as a solid or liquid.In nature, rocks melt for one of two reasons. First, rocks melt when they are heated to their melting points. This could occur, for example, when hot mantle rocks migrate toward the surface and come into contact with crustal rocks having lower melting points. The volcanic activity in the region that includes Yellowstone National Park is believed to have resulted from such activity. Here basaltic magma that formed in the mantle transported heat into the crust, where partial melting of crustal rocks generated silica-rich magmas. Second, without increasing temperature, a reduction in the confining pressure can lower the melting temperature sufficiently to trigger melting. This occurs whenever rock ascends, thereby moving into a region of lower pressure. Both processes are thought to play significant roles in magma formation.Most basaltic magmas are believed to originate from the partial melting of the rock peridotite, the major constituent of the upper mantle. Laboratory studies confirm that partial melting of this dry, silica poor rock produces magma having a basaltic composition. Since mantle rocks exist in environments that are characterized by high temperatures and pressures ,melting often results from a reduction in confining pressure. This can occur, for example, where mantle rock ascends as part of a slow-moving convection cell.Due to the fact that basaltic magmas form many kilometers below the surface, we might expect that most of this material would cool and crystallize before reaching the suface. However, as dry basaltic magma moves upward, the confining pressure steadily diminishes and further reduces the melting point. Basaltic magmas appear to ascend rapidly enough so that as they enter cooler environments the heat loss is offset by a drop in the melting point. Consequently, large outpourings of basaltic magmas are common on the earth’s surface.Conversely, granitic magmas are thought to be generated by partial melting of water-rich rocks that were subjected to increased temperature. As a wet granitic melt rises, the confining pressure decreases, which in turn reduces the effect of water on lowering the melting temperature. Further, granitic melts are high’in silica and thus more viscous than basaltic melts. Thus, in contrast to basaltic magmas that produce vast outpourings of lava, most granitic magmas lose their mobility before reaching the surface and therefore tend to produce large intrusive features such as batholiths. On those occasions when silica rich magmas reach the surface, explosive pyroclastic flows,such as those that produced the Yellowstone Plateau, are the rule.Even though most magma is thought to be generated by partial melting, once formed the composition of a magma body can change dramatically with time. For example, as a magma body migrates upward, it may incorporate some of the surrounding country rock. As the country rock is assimilated, the composition of the magma is altered. Further, recall from our discussion of Bowen’s reaction series that during solidification, magma often undergoes fractional crystallization. This produces a magma quite unlike the parent material. These processes account, at least in part, for the fact that a single volcano can extrude lavas with a wide range of chemical compositions.。