2015年2月GMAT阅读机经(火山熔浆的形成)

有条不紊的复习才能让你更好的应对考试。以下是查字典出国留学网GMAT考试栏目为大家整理的2015年2月GMAT阅读机经，供大家参考!

2015年2月GMAT阅读机经——火山熔浆的形成

(关键词: Lava，melting, 希望对考古有帮助)

通篇反正就是在说科学家在研究火山熔浆形成的过程中发生了哪些化学反应(有题问这文章主要讲什么，选这个)，然后说了几个实验，具体内容不记得，然后第二段说在海底发现的lava sample里面又出现了和第一段相反的情况，然后又说了对于这个情况的两种解释，第一种还是有问题，作者认为第二种更靠谱，第二种有提到通过small channels之类的东西在什么之前就完成了化学反应，之后就不会再有反应了(这里有题)

还有一篇是lava的，我找的13年7月的，我看到的和这个基本一致，这篇不长，1屏不到

P1讲火山爆发来源于Mantle中的Lava，而Lava来源于Melt ，Melt在向地表上升的过程中会与Mantle中的Rock反应并不断互相交换物质、变化结构，即吸收Orthopyroxene并排出Olivine。越接近closer表面surface，lava的exchange越频繁

P2一个跟理论不太相符的事情，一种海底里的lava sample，在距离地表45千米突然发现已经停止这种物质交换，Melt的结构不变了。一种假设是那里的Mantle太松散了，使Melt无法与他们接触并交换物质，但立即被否定了(因为45KM还很深东西都很软，没有裂缝)。另一种假设是Melt在之前的上升过程中已经吸收了足够的Orthopyroxene， 并将能排出的Olivine都排了，无法继续反应。

最后一篇我连一个关键词都想不起来了，想要考古找内容帮大家也不行啦，大家参考别的狗狗吧~

V1 duke3d001 750, wade777, echosweet 700 & yueqianchen

关键词：45KM, Olivine, Orthopyroxene (referenced by gitarrelieber)。这篇文章的题目不难，狗的骨架也很清晰。

第一段讲火山爆发来源于Mantle中的Lava，而Lava来源于Melt ，Melt在向地表上升的过程中会与Mantle中的Rock反应并不断互相交换物质、变化结构，即吸收Orthopyroxene并排出Olivine。

第二段说一个跟理论不太相符的事情，一种海底里的lava sample，在距离地表45千米突然发现已经停止这种物质交换，Melt的结构不变了。一种假设是那里的Mantle太松散了，使Melt无法与他们接触并交换物质，但立即被否定了(因为45KM还很深东西都很软，没有裂缝)。另一种假设是Melt在之前的上升过程中已经吸收了足够的Orthopyroxene， 并将能排出的Olivine都排了，无法继续反应。

1 darkchoco 710是什么可以证明这种exchange的存在：熔岩的成分

2 gyz12 740 一道文章最后句定位：Olivine的用完了,exchange就停止了

3 gyz12 740 一道是选chemical composition为特征 sashimiyuki 720 V37 选“lab experiments” indicate 那个melt 的变化的，没有选chemical composition, 细节题定位后决定的，确认后到现在还没有深深后悔过

4 tianmo0512 是什么发生反应：选melt

5 feifeizoe 750 V39 文中什么情况下描述了那种正常的exchange：lab experiment中实现了那种现象

6 The author mention “the melt to rise so rapidly” in order to：提出了一种hypothesis，这种hypothesis在后面被反驳

(疑似)原文未缩减 gitarrelieber (sereneys 730 V40 基本确认)

节选自The Origin of the Land under the Sea (Scientific American Magazine @ February 2009)

Author: Peter B. Kelemen

Knowledge of the intense heat and pressure in the mantle led researchers to hypothesize in the late 1960s that ocean crust originates as tiny amounts of liquid rock known as melt—almost as though the solid rocks were “sweating.” Even a minuscule release of pressure (because of material rising from its original position) causes melt to form in microscopic pores deep within the mantle rock. Explaining how the rock sweat gets to the surface was more difficult. Melt is less dense than the mantle rocks in which it forms, so it will constantly try to migrate upward, toward regions of lower pressure. But what laboratory experiments revealed about the chemical composition of melt did not seem to match up with the composition of rock samples collected from the mid-ocean ridges, where eruptedmelt hardens. Using specialized equipment to heat and squeeze crystals from mantle rocks in the laboratory, investigators learned that the chemical composition of melt in the mantle varies depending on the depth at which it forms; the composition is controlled by an exchange of atoms between the melt and the minerals that makeup the solid rock it passes through. The experiments revealed that as melt rises, it dissolves one kind of mineral, orthopyroxene, and precipitates, or leaves behind, another mineral, olivine. Researchers could thus infer that the higher in the mantle melt formed, the more orthopyroxene it would dissolve, and the more olivine it would leave behind.(melt上升时， 溶解Ort产生Oli, 所以melt higher， 溶解的Ort越多，产生的/留在身后的Oli也越多) Comparing these experimental findings with lava samples from the mid-ocean ridges revealed that almost all of them have the composition of melts that formed at depths greater than 45kilometers. This conclusion spurred a lively debate about how meltis able to rise through tens of kilometers of overlying rock while preserving the composition appropriate for a greater depth. If melt rose slowly in smallpores in the rock, as researchers suspected, it would be logical to assume that all melts would reflect the composition of the fashallowest part of the mantle,at 10 kilometers or less. Yet the composition of most mid-ocean ridge lavas amples suggests their source melt migrated through the uppermost 45 kilometers of the mantle without dissolving any orthopyroxene from the surrounding rock. But how? (疑大概为狗狗第一段的背景内容)

In the early 1970s scientists proposed an answer: the melt must make the last leg of its upward journey along enormous cracks. Open cracks would allow the melt to rise so rapidly that it would not have time to interact with the surrounding rock, nor would melt in the core of the crack ever touch the sides. Although open cracks are not a natural feature of the upper mantle— the pressure is simply too great—some investigators suggested that the buoyant force of migrating melt might sometimes be enough to fracture the solid rock above, like an icebreaker ship forcing its way through polar pack ice. Adolphe Nicolas of the University of Montpellier in France and his colleagues discovered tantalizing evidence for such cracks while examining unusual rock formations called ophiolites. Typically, when oceanic crust gets old and cold, it becomes so dense that it sinks back into the mantle along deep trenches known as subduction zones, such as those that encircle the Pacific Ocean. Ophiolites, on the other hand, are thick sections of old seafloor and adjacent, underlying mantle that are thrust up onto continents when two of the planet’s tectonic plates collide. A famous example, located in the Sultanate of Oman, was exposed during the ongoing collision of the Arabian and Eurasian plates. In this and other ophiolites, Nicolas’s team found unusual, light-colored veins called dikes, which they interpreted as cracks in which melt had crystallized before reaching the seafloor. The problem with this interpretation was that the dikes are filled with rock that crystallized from a melt that formed in the uppermost reaches of the mantle, not below 45 kilometers, where most mid-ocean ridge lavas originate. In addition, the icebreaker scenario may not work well for the melting region under mid-ocean ridges: below about 10 kilometers, the hot mantle tends to flow like caramel left too long in the sun, rather than cracking easily.

To explain the ongoing mystery, I began working on an alternative hypothesis for lava transport in the melting region. In my dissertation in the late 1980s, I developed a chemical theory proposing that as rising melt dissolves orthopyroxene crystals, it precipitates a smaller amount of olivine, so that the net result is a greater volume of melt. Our calculations revealed how this dissolution process gradually enlarges the open spaces at the edges of solid crystals, creating larger pores and carving a more favorable pathway through which melt can flow. As the pores grow, they connect to form elongate channels. In turn, similar feedbacks drive the coalescence of several small tributaries to form larger channels. Indeed, our numerical models suggested that more than 90 percent of the melt is concentrated into less than 10 percent of the available area. That means millions of microscopic threads of flowing melt may eventually feed into only a few dozen, high porosity channels 100 meters or more wide. Even in the widest channels, many crystals of the original mantle rock remain intact, congesting the channels and inhibiting movement of the fluid. That is why melt flows slowly, at only a few centimeters a year. Over time, however, so much melt passes through the channels that all the soluble orthopyroxene crystals dissolve away, leaving only crystals of olivine and other minerals that the melt is unable to dissolve. As a result, the composition of the melt within such channels can no longer adjust to decreasing pressure and instead records the depth at which it last “saw” an orthopyroxene crystal. One of the most important implications of this process, called focused porous flow, is that only the melt at the edges of channels dissolves orthopyroxene from the surrounding rock; melt within the inner part of the conduit can rise unadulterated.

V1

第一段：说的是火山爆发中熔岩(lava)是来自地幔的(mantle)，说是由地下升起来的，在此过程中成分变化,一种物质O1(O打头)增加，另一个O2(也是O打头)减少。

第二段：海底火山样本大概都证明了，但是奇怪的是45KM时成分就不变了，这是怎么回事呢?若是不变它如何上来的呢?第一种解释说是沿着裂缝上来的(crack)，然后说不可能啊，因为45KM还很深东西都很软，没有裂缝。第二种解释又说，到45KM时O2就用完了 - 题目实在记不起来记得都挺好找的

V2

还有lava的那个

第一段是一个试验说从mantle 怎样就变成了melt 然后说越靠近surface越多 Ose。。很长一个单词 然后越少 Olive之类的一个单词。

第二段说在可是ocean land里面 45km以下就没有这种substance的exchange 然后就分析原因 有一个是rock太软不会裂开怎么流不出去还有几个解释忘记了

文言文 nowwsy & XYXB 未确认

V1 bhj & parkmm V34 & zebracxy 730 V38 (Golden 综合版)

是火山，说火山喷发，喷出来一种叫什么"mamgo"(M)的东西(不确定是不是这个词)

地质学家一直认为M这个东西是在地底下很久了，这个东西一旦喷出来以后，更下面的这个东西会重新填满喷出去的区域。但是有人站出来说这种观点是不对的，因为如果是这样，是不稳定的，火山会继续喷发。然后说，最近研究了一个在火山岩里面的一个晶体，叫"Zinroc"的东西(不确定是不是这个词)。说这里面的氧的含量和在很深的地底下的M的含氧量是不一样的。按照前面的假说，这两个含氧量应该是一样的。而含氧量又和雨水里面的含氧量一致。所以说，那个M喷发出来以后是地表的石头掉下去又形成的新的M。

1、主题题。

2、在很深的地底下的M会怎么样。一个选项是说那些东西在那里几百万年了，还有一个选项说这个东西没有那个Z什么的，还有一个选项说含氧量不一样。我不确定答案。

3、地下的mamgo怎么了，答“丛地面陷下去的” (这题很sure)

4、知道第一次喷发的岩浆怎么样，我选了含氧量不一样，供参考!

希望以上《2015年2月GMAT阅读机经(火山熔浆的形成)》一文能给大家提供帮助!

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