GMAT閱讀機(jī)經(jīng)整理：火山熔巖.

　　3月2日換庫(kù)后，小編為大家整理這個(gè)月的GMAT閱讀機(jī)經(jīng)，這篇GMAT閱讀機(jī)經(jīng)是關(guān)于火山熔巖的文章，考生朋友可以看看，下面的內(nèi)容為考古內(nèi)容，分享給大家，希望對(duì)大家有所幫助，文中觀點(diǎn)僅供參考。

　　[V1]

　　那篇文章說(shuō)的是under the sea 的火山，有說(shuō)lava怎么melt怎么形成，然后說(shuō)它會(huì)在往上的過(guò)程中和周?chē)奈镔|(zhì)發(fā)生元素交換什么的，但是這種痕跡只在較深(或者是較淺)的地方有，另外一段就沒(méi)有。第二段，有科學(xué)家猜測(cè)是因?yàn)樗俣忍炝藖?lái)不及交換，但是實(shí)驗(yàn)證明在那種壓強(qiáng)下是不可能快的。然后又提出一種假設(shè)說(shuō)是之前交換完了，就不再交換了

　　[V2]

　　第一篇是講熔巖lava的但是和寂靜里面說(shuō)的都不一樣，不是講如何補(bǔ)充的，而是第一段先講了一個(gè)理論，說(shuō)是越接近c(diǎn)loser表面surface，lava的exchange越頻繁;然后第二段講了一個(gè)反例，就是科學(xué)家發(fā)現(xiàn)海底火山與眾不同，在海平面450米以下的火山根本就不exchange!按理來(lái)說(shuō)海底火山更接近地球表面應(yīng)該更多地exchange，但是這個(gè)結(jié)果就讓科學(xué)家覺(jué)得很puzzled. 然后就有兩種假說(shuō)，第一種是說(shuō)不是不exchange，而是flow too rapid(這里好像還有一個(gè)什么什么crack...的詞)，第二種解釋是啥我忘了，好像是直接反駁第一段的結(jié)論的。后面有主旨題，我選的是argue了第一段的假設(shè)(我也覺(jué)得不是很貼切，但是其他四個(gè)都不是特別好...)。

　　[V3]

　　1)“后面有主旨題，我選的是argue了第一段的假設(shè)(我也覺(jué)得不是很貼切，但是其他四個(gè)都不是特別好...)。 ” 完了我又沒(méi)選這個(gè) 這是A選項(xiàng)，其他確實(shí)不好這篇主旨題大家好好看看!!!

　　2)"feifeizoe 750 V39 文中什么情況下indicate 那種正常的exchange：lab experiment中實(shí)現(xiàn)了那種現(xiàn)象" “gyz12 740 一道是選chemical composition為特征 sashimiyuki 720 V37 選“l(fā)ab experiments” indicate 那個(gè)melt 的變化的，沒(méi)有選chemical composition, 細(xì)節(jié)題定位后決定的，確認(rèn)后到現(xiàn)在還沒(méi)有深深后悔過(guò)”

　　我表示我好像選錯(cuò)了 750 740 大牛都這么說(shuō)了 大家跟吧。。。。。。深深地憂傷 錯(cuò)了好多555…

　　3)“The author mention “the melt to rise so rapidly” in order to：提出了一種hypothesis，這種hypothesis在后面被反駁 ” 確認(rèn)考題!!!!!!就這么干!!!!

　　[V4]

　　說(shuō)lava是怎么怎么形成，上升過(guò)程中不斷和某種東西交換物質(zhì)，就是寂靜上說(shuō)的那個(gè)orthopyroxene和olivine。然后第二段轉(zhuǎn)折說(shuō)不對(duì)啊，什么海洋中有個(gè)什么sample，在45Km處就停止交換了，所有條件和第一段一樣，所以詫異。然后有一個(gè)假設(shè)說(shuō)什么忘記了(此處有題highlight了一整個(gè)假設(shè)的內(nèi)容，問(wèn)這個(gè)是干什么的干活。)，但是立馬被否定了，作者提出了另一種假設(shè)，就是已經(jīng)交換完了，沒(méi)有了，不能交換了，說(shuō)這個(gè)比較合理。

　　還有個(gè)題問(wèn)第一段中說(shuō)放出orthopyroxene和olivine是哪里得到的結(jié)論，答案做實(shí)驗(yàn)(讀下一整個(gè)句子，最開(kāi)始說(shuō)experiments explained之類(lèi)的話)

　　考古已確認(rèn)(本月狗主說(shuō)考題像下面原文的縮減，作為重點(diǎn)讀一下吧~)

　　★火山熔巖的來(lái)由

　　V1

　　關(guān)鍵詞：45KM, Olivine, Orthopyroxene (rerenced by gitarrelieber)。這篇文章的題目不難，狗的骨架也很清晰。

　　第一段講火山爆發(fā)來(lái)源于Mantle中的Lava，而Lava來(lái)源于Melt ，Melt在向地表上升的過(guò)程中會(huì)與Mantle中的Rock反應(yīng)并不斷互相交換物質(zhì)、變化結(jié)構(gòu)，即吸收Orthopyroxene并排出Olivine。

　　第二段說(shuō)一個(gè)跟理論不太相符的事情，一種海底里的lava sample，在距離地表45千米突然發(fā)現(xiàn)已經(jīng)停止這種物質(zhì)交換，Melt的結(jié)構(gòu)不變了。一種假設(shè)是那里的Mantle太松散了，使Melt無(wú)法與他們接觸并交換物質(zhì)，但立即被否定了(因?yàn)?5KM還很深東西都很軟，沒(méi)有裂縫)。另一種假設(shè)是Melt在之前的上升過(guò)程中已經(jīng)吸收了足夠的Orthopyroxene， 并將能排出的Olivine都排了，無(wú)法繼續(xù)反應(yīng)。

　　1 是什么可以證明這種exchange的存在：熔巖的成分

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

　　3 一道是選chemical composition為特征 選“l(fā)ab experiments” indicate 那個(gè)melt 的變化的，沒(méi)有選chemical composition, 細(xì)節(jié)題定位后決定的，確認(rèn)后到現(xiàn)在還沒(méi)有深深后悔過(guò)

　　4 是什么發(fā)生反應(yīng)：選melt

　　5 文中什么情況下描述了那種正常的exchange：lab experiment中實(shí)現(xiàn)了那種現(xiàn)象

　　6 The author mention “the melt to rise so rapidly” in order to：提出了一種hypothesis，這種hypothesis在后面被反駁

　　(疑似)原文未縮減

　　節(jié)選自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上升時(shí)，溶解Ort產(chǎn)生Oli, 所以melt higher， 溶解的Ort越多，產(chǎn)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 rlect 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? (疑大概為狗狗第一段的背景內(nèi)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 bore 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 lt 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.

　　以上就是關(guān)于火山熔巖這篇GMAT閱讀機(jī)經(jīng)的全部?jī)?nèi)容，考生可以有選擇的看看，機(jī)經(jīng)雖好，但是也要適度喲。最后祝大家都能考出好成績(jī)。