巖漿成因外文翻譯

1、<p><b>　　中文1623字</b></p><p><b>　　巖漿成因</b></p><p>　　基于現(xiàn)有的科學(xué)證據(jù)顯示，地球的地殼和地幔主要由堅(jiān)硬的巖石組成。另外，外核呈流體狀態(tài)，這種材料是非常密集并保持在地球內(nèi)部深處的。那么，什么是產(chǎn)生地球上的火山活動(dòng)的巖漿源？</p><p>　　我們知道，巖漿

2、在巖石被加熱到其熔點(diǎn)時(shí)生成。在近地表環(huán)境，花崗巖在800℃左右的溫度下開始融化，而??玄武巖必須達(dá)到1000℃以上。一個(gè)重要的差異存在于單一物質(zhì)和化合物之間，例如冰和幾種不同的礦物混合成的火成巖的熔點(diǎn)。冰融化在一定的溫度下，而大部分火成巖在幾百度的溫度范圍內(nèi)熔融。巖石被加熱時(shí)，第一個(gè)形成液體的包含一個(gè)比原巖百分比高的低融點(diǎn)礦物。如果繼續(xù)熔化，該熔體將穩(wěn)步接近從巖石的整體組成。然而，大多數(shù)情況下，熔融是不完整的。這個(gè)過程被稱為部分熔融，不

3、全部生成巖漿。</p><p>　　部分熔融的結(jié)果明顯比母巖熔融產(chǎn)生的二氧化硅含量高?；叵胍幌?，玄武質(zhì)巖石具有較低的硅含量，花崗質(zhì)巖石具有更高的硅含量。因此，部分熔融產(chǎn)生的巖漿比他們從母巖形成更接近于花崗巖成分。正如我們將看到的，這個(gè)想法將有助于我們了解全球分布的各種類型的火山活動(dòng)。</p><p>　　巖石熱的來源是什么？來源之一被認(rèn)為是集中在上地幔和地殼的放射性元素衰變過程中釋放的熱量

4、。在地下礦井的工人很早就認(rèn)識(shí)到溫度隨深度增加。雖然增長率因地而異，它被認(rèn)為是平均上升每公里增加20℃到30℃。這種溫度隨著深度逐漸增加，稱為地?zé)崽荻取?lt;/p><p>　　如果溫度是決定巖石融化的唯一因素，地球?qū)⒊蔀閮H覆蓋著薄薄一層固體外殼的熔融球。然而，壓力也隨深度而增加。由于巖石受熱膨脹，為了克服圍壓的影響，巖石融化需要額外的熱量。在一般情況下，圍壓的增加會(huì)導(dǎo)致巖石的熔點(diǎn)提高。影響巖石熔點(diǎn)的另一個(gè)重要因素是它

5、的水含量。歸結(jié)到一點(diǎn)，水越多熔點(diǎn)越低。水對(duì)降低熔點(diǎn)的效果被增加的壓力放大。因此，在同壓力下“濕”巖石比具有相同成分“干”巖石的熔點(diǎn)低。因此，除了巖石的組合物，溫度，壓力和水的含量確定巖石作為固體或液體存在。</p><p>　　在自然界中，巖石融化的原因有兩個(gè)。第一，加熱到其熔點(diǎn)時(shí)巖石融化。這可能發(fā)生，例如，當(dāng)熱地幔巖向表面遷移并接觸到地殼巖石具有較低的熔點(diǎn)。在該地區(qū)，包括黃石公園火山的活動(dòng)導(dǎo)致這樣的活動(dòng)。這里玄

6、武質(zhì)巖漿在地幔中形成的熱運(yùn)到地殼，那里的地殼巖石部分熔融產(chǎn)生的富硅巖漿。第二，沒有溫度的增加，圍壓的降低可以降低熔融溫度足以觸發(fā)熔化。每當(dāng)發(fā)生巖石上升，從而移動(dòng)到較低壓力的區(qū)域。這兩個(gè)過程都被認(rèn)為是在巖漿的形成中起重要的作用。</p><p>　　大多數(shù)的玄武質(zhì)巖漿被認(rèn)為起源于橄欖巖部分熔融的巖石，是上地幔的主要成分。實(shí)驗(yàn)室研究證實(shí)，干燥，不富含二氧化硅的巖石部分熔融產(chǎn)生有玄武巖組成的巖漿。因?yàn)樵诟叩臏囟群蛪毫Νh(huán)

7、境下存在的地幔巖石，融化的結(jié)果往往是在圍壓的降低。這可能發(fā)生，例如，其中地幔巖石作為一個(gè)緩慢移動(dòng)的對(duì)流單元的一部分上升。</p><p>　　由于玄武質(zhì)巖漿形成在地表以下幾公里，我們可以預(yù)計(jì)，這些材料大部分將在到達(dá)表面冷卻并結(jié)晶。然而，由于干燥的玄武巖巖漿向上移動(dòng)，圍壓的穩(wěn)步減少，進(jìn)一步降低了熔點(diǎn)。玄武質(zhì)巖漿出現(xiàn)快速上升足以使他們進(jìn)入較冷的環(huán)境中的熱損失的熔點(diǎn)下降所抵消。因此，大爆發(fā)的玄武質(zhì)巖漿是常見在地球表面。

8、</p><p>　　相反，花崗質(zhì)巖漿被認(rèn)為是由富含水的巖石部分熔融進(jìn)行溫度升高產(chǎn)生。作為一個(gè)潮濕的花崗質(zhì)熔點(diǎn)上升，圍壓減小，從而減少水對(duì)降低熔融溫度的影響。此外，花崗質(zhì)熔體比玄武質(zhì)巖漿含二氧化硅更多和更粘。因此，對(duì)比玄武質(zhì)巖漿產(chǎn)生巨大的流出的熔巖，大多數(shù)花崗質(zhì)巖漿在失去流動(dòng)性之前到達(dá)地面，因此往往會(huì)產(chǎn)生較大的侵入特征如巖基。在這些場(chǎng)合時(shí)，富硅巖漿到達(dá)地表，爆炸性的火山碎屑流，如那些產(chǎn)生的黃石高原。</p&

9、gt;<p>　　盡管大多數(shù)巖漿被認(rèn)為是部分熔融產(chǎn)生，一旦形成的巖漿體組合物可以隨時(shí)間顯著變化。例如，作為巖漿體向上運(yùn)移，它可能包含了一些周圍的巖石。由于圍巖同化，巖漿的成分改變。此外，回想起我們討論鮑文反應(yīng)系列，在凝固過程中，巖漿經(jīng)常發(fā)生分離結(jié)晶。這將產(chǎn)生一個(gè)完全不同于母體點(diǎn)巖漿。考慮這些過程，至少部分地，即一個(gè)單一的火山可以具有寬范圍的化學(xué)組成的拉伸性熔巖。</p><p><b>　

10、　外文原文</b></p><p>　　Origin of Magma</p><p>　　Based on available scientific evidence, the earth’s crust and mantle are composed primarily of solid rock. Further, although the outer core is i

11、n 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?</p><p>　　We know that magma can be produced when

12、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 b

13、egin. 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 me

14、lts at a definite te</p><p>　　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 co

15、ntent 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.

16、 As we shall see, this idea will help us to understand the global distribution of the various types of </p><p>　　What is the heat source to melt rock? One source is the heat liberated during the decay of rad

17、ioactive 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 plac

18、e 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. </p><p>　　If temperature were t

19、he 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 he

20、at 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 increase in the rock’s melting point. Another important factor affecti

21、ng the melting point of rock is its wat</p><p>　　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 r

22、ocks 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 act

23、ivity. Here basaltic magma that formed in the mantle transported heat into the crust, where partial melting of crustal roc</p><p>　　Most basaltic magmas are believed to originate from the partial melting of

24、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 envi

25、ronments 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-mo</p><

26、;p>　　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

27、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

28、 melting point. Consequently, large outpourings of basaltic magmas a</p><p>　　Conversely, granitic magmas are thought to be generated by partial melting of water-rich rocks that were subjected to increased t

29、emperature. 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

30、than basaltic melts. Thus, in contrast to basaltic magmas that produce vast outpourings of lava, most granitic magmas lose their mobility before reachi</p><p>　　Even though most magma is thought to be genera

31、ted 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

32、 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