攒rp系列之五,本月阅读夏威夷岛链文章(附pdf背景全文)

ohohh

今天看到好几个nn都考到了夏威夷岛链,早上做完模考就在网上狂搜相关资料, 望考过的nn确认一下是否相关,
强烈推荐大家下载附件里的整篇夏威夷文章,和考试的思路一致,所有生词里面都有的.

第一篇 ( 我只摘了三段,具体见附件,我觉得和nn刚写的基金一致)

The evidence that clinched the case for plate tectonics in the 1960s, and that has since refined our understanding of hotspots, is the record of plate movement provided by rock magnetization. When lava cools, magnetic minerals within it, principally magnetite and titanomagnetite, crystallize. These miniature bar magnets lock in the direction of the earth’s magnetic field at that moment in time and that location on the surface.

Because the earth’s magnetic field varies in both time and space, rock magnetization provides two ways to determine how plates have moved. First, geologists can study the time variation. At irregular time intervals, the planet’s field reverses polarity: the North and South magnetic poles switch places. Consider what that means for lava erupting at mid-ocean ridges. When the rock emerges and cools, the magnetization of its minerals lines up like magnetic filings pointing, say, to the north. Plate tectonics then carries the rocks away from the ridge. After several hundred thousand years or so, the polarity flips, and from that moment newly formed rocks are magnetized the opposite way. These, too, are carried away from the ridge. The polarity eventually flips back, and the cycle continues. The result is a series of horizontal stripes recorded in the oceanic crust, alternating between north-pointing and south-pointing magnetic minerals—a geologic version of tree rings. Geologists date the stripes by matching them against the timeline of polarity reversals. They then use time and distance data to calculate a plate’s direction and speed rela­tive to an adjoining plate.

The second technique exploits the fact that the direction of the earth’s magnetic field has two components: horizontal (declination) and vertical (inclination). When you rely on a com­pass to find the direction of north, you use the declination, but if you look closely at the com­pass needle, you will see that it is also tilted slightly with respect to the horizontal. As Neil Opdyke of the University of Florida demon­strated in a classic study in the late 1960s, the inclination is directly related to latitude. Mea­suring inclination reveals the latitude where the rock originally formed and hence the minimum distance that the plate must have moved since then.
(第二篇)The surface manifestations of plumes, that is, columns of hot material, that rise from deep in the Earth's mantle. Hot spots are widely distributed around the Earth. One of their characteristics is an abundance of volcanic activity which persists for long time periods (greater than 1 million years). When the lithosphere (the rigid outer layer of the Earth) moves over a plume, a chain of volcanoes is left behind that progressively increases in age along its length. Hot spots are believed to be fixed with respect to each other and the deep mantle so that the age and orientation of these chains provide information on the absolute motions of the tectonic plates. See also Lithosphere; Plate tectonics.


The Hawaiian-Emperor seamount chain in the central Pacific Ocean is a good example of a volcanic chain that was generated at a hot spot. The 3400-mi-long (5700-km) chain is made up mainly of tholeiitic lavas and ash tuff and pumice deposits. The lavas may have evolved from an initial submarine shield-building stage, through an explosive stage as they build up to sea level, and finally to a subaerial post-erosional stage. See also Lava; Seamount and guyot.

Not all hot-spot volcanism is expressed in terms of highly lineated, multistage, volcanic chains. Aseismic ridges that extend up to or close to the axes of mid-oceanic ridges are another example of hot-spot volcanism. When a hot spot (for example, Iceland) is centered on the axis, pairs of ridges such as the Iceland-Faeroes Rise and the Greenland Rise are formed. Sometimes the plate (for example, Africa) has migrated off the hot spot (such as Tristan da Cunha), leaving behind ridge systems that no longer extend to the ridge axis (such as Rio Grande Rise and Western Walvis). See also Mid-Oceanic Ridge; Volcano; Volcanology.

Another characteristic of hot spots is their association with broad swells in the Earth's topography. The Hawaiian hot-spot swell is believed to have been formed in response to either thermal or dynamic effects in an underlying mantle plume. The crustal and upper-mantle structure, which is constrained by seismic refraction data, shows that the oceanic crust is of uniform thickness beneath the swell. The long-wavelength correlation that is observed between the gravity anomaly and the topography (about 37 mGal mi?1 or 22 mGal km?1) indicates that the mass excess of the swell is compensated by a low-density, high-temperature region below the crust. The uplift of hot-spot swells is believed to result from thermal perturbations in the underlying plume. The excess heights of swells suggest, on isostatic grounds, that temperature differences of about 450°F (250°C) occur between the plume and the surrounding mantle. Hot ascending plumes may raise the temperature of the overlying lithosphere, thereby thinning it.

Two classes of models have been proposed to explain hot-spot swells. In the reheating model, uplift is produced by thermal expansion that is confined to the conducting portion of the lithosphere (the thermal boundary layer). In the dynamic model, however, there is a contribution to the uplift that is produced by vertical normal stresses exerted to the seismically defined base of the lithosphere (the mechanical boundary layer) by convection.

The main distinguishing feature between the uplift models is that the reheating model predicts a higher heat flow than the dynamic model. Discrimination between these models therefore depends on how the subsidence history, heat flow, and long-term strength (which is controlled mainly by the temperature) differ from those for unperturbed lithosphere of the same age.

童言无忌

thanks for sharing!

DanielSSSS

感谢楼主...

melodyflying

不过考到这篇文章应该算是高分区了吧

xz328

这篇文章不是原文，但有很多专业的词汇都是一样的。建议后面考得同学把这篇文章的背景搞清楚。考试时候的文章又长又难……

feir2004

厉害！！！！！！！！！！！

heavennancy

好厉害啊，谢谢谢谢

ohohh

还有考过的牛牛帮我看看这pdf有相似的地方吗

melodyflying

大家如果觉得夏威夷岛链还是不通透（个人觉得钩钩里实在是让人一头雾水的样子）可以看看ohohh发的这个第一篇。认真分析过就会基本知道什么hotspot和moved plate到底是怎么回事，文章到底想说啥了。
不过文章很长，一上来就看太困难，我找到了一个中文翻译网页（连书的图片版式都一样）可以先看中文，在定位英文~http://www.docin.com/p-6501917.html
看完再结合钩钩就悟了~

-- by 会员 piggyuu (2009/11/9 19:19:26)

好多啊 都不知道应该看到哪里是个头啊

ohohh

XYXB是强悍。。。。

-- by 会员 4mmgirl (2009/11/9 21:50:14)

她是超女,如果说CD有明星的话,她绝对算是其中的巨星.