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地球表面并不是由一整块构成地壳的岩石构成的，而是由许多紧密相连的“构造板块”组成，就像巨大的拼图一样。

Earth’s surface is not made up of a single sheet of rock that forms a crust but rather a number of “tectonic plates” that fit closely, like the pieces of a giant jigsaw puzzle.

有些板块携带岛屿或大陆；其他的则形成海底。

Some plates carry islands or continents; others form the seafloor.

所有这些板块都在缓慢移动，因为它们都漂浮在密度更大的半流体地幔上，也就是地壳和地核之间的那一层。

All are slowly moving because the plates float on a denser semiliquid mantle, the layer between the crust and Earth’s core.

这些板块的边缘有扩张的脊线（两个板块正在分离，新的海底正在形成），俯冲带（两个板块碰撞，一个板块俯冲到另一个板块之下），或者转换断层（两个板块既不聚合也不分离，只是互相移动）。

The plates have edges that are spreading ridges (where two plates are moving apart and new seafloor is being created), subduction zones (where two plates collide and one plunges beneath the other), or transform faults (where two plates neither converge nor diverge but merely move past one another).

地球上大部分的火山活动和地震活动都发生在板块之间的边界上。

It is at the boundaries between plates that most of Earth’s volcanism and earthquake activity occur.

一般来说，板块的内部在地质上是平静的。

Generally speaking, the interiors of plates are geologically uneventful.

只要看一眼太平洋的地图就会发现，在遥远的海面上有许多岛屿实际上是火山——许多岛屿不再活动，有些岛屿上长满了珊瑚——它们起源于构成太平洋海底的太平洋板块内部的活动。

A glance at a map of the Pacific Ocean reveals that there are many islands far out at sea that are actually volcanoes—many no longer active, some overgrown with coral—that originated from activity at points in the interior of the Pacific Plate that forms the Pacific seafloor.

火山活动是如何在远离板块边界的地方发生的呢？

How can volcanic activity occur so far from a plate boundary?

夏威夷群岛提供了一个很有启发性的答案。

The Hawaiian Islands provide a very instructive answer.

像许多其他的岛群一样，它们形成了一个岛链。

Like many other island groups, they form a chain.

夏威夷岛链从夏威夷岛向西北延伸。

The Hawaiian Island Chain extends northwest from the island of Hawaii.

19世纪40年代，美国地质学家詹姆斯·戴利（James Daly）曾观察到，夏威夷群岛的不同地区似乎有着相似的地质演化过程，但在向西北方向发展的过程中，岛屿受到侵蚀的程度越来越严重，因此，这些岛屿可能更古老。

In the 1840s American geologist James Daly observed that the different Hawaiian Islands seem to share a similar geologic evolution but are progressively more eroded, and therefore probably older, toward the northwest.

然后在1963年，在板块构造理论发展的早期，加拿大地球物理学家图佐·威尔逊（Tuzo Wilson）意识到，如果这些岛屿是在一个移动在内部固定的火山源上的表面板块上形成的，那么这个年龄的发展是可能的。

Then in 1963, in the early days of the development of the theory of plate tectonics, Canadian geophysicist Tuzo Wilson realized that this age progression could result if the islands were formed on a surface plate moving over a fixed volcanic source in the interior.

威尔逊认为，从夏威夷向西北延伸的长链火山仅仅是位于地幔构造板块之下的一个长期存在的火山源的表面表现。

Wilson suggested that the long chain of volcanoes stretching northwest from Hawaii is simply the surface expression of a long-lived volcanic source located beneath the tectonic plate in the mantle.

今天最西北的岛屿可能是最早形成的。

Today’s most northwestern island would have been the first to form.

然后，当板块缓慢地向西北移动时，新的火山岛就会在板块移动到火山源上方时形成。

Then, as the plate moved slowly northwest, new volcanic islands would have formed as the plate moved over the volcanic source.

最近的一个岛屿是夏威夷岛，它位于这条岛链的末端，现在位于火山源头的上方。

The most recent island, Hawaii, would be at the end of the chain and is now over the volcanic source.

尽管这个想法没有立即被接受，夏威夷（和其他）岛链的年代表明，它们的年龄在远离当前活火山的地方增加，正如戴利提出的那样。

Although this idea was not immediately accepted, the dating of lavas in the Hawaiian (and other) chains showed that their ages increase away from the presently active volcano, just as Daly had suggested.

威尔逊对这些数据的分析现在是板块构造学的核心部分。

Wilson’s analysis of these data is now a central part of plate tectonics.

人们认为，出现在板块内部的大多数火山是由地幔柱形成的，地幔柱是指从地幔深处升起的熔融岩石。

Most volcanoes that occur in the interiors of plates are believed to be produced by mantle plumes, columns of molten rock that rise from deep within the mantle.

只要火山在地幔柱之上，它就仍然是一个活跃的“热点”。

A volcano remains an active “hot spot” as long as it is over the plume.

这些地幔柱显然起源于很深的地方，可能深达地核和地幔之间的边界，而且已经活跃了很长时间。

The plumes apparently originate at great depths, perhaps as deep as the boundary between the core and the mantle, and many have been active for a very long time.

夏威夷热点地带最古老的火山已经有将近8000万年的历史了。

The oldest volcanoes in the Hawaiian hot-spot trail have ages close to 80 million years.

其他岛屿，包括太平洋上的塔希提岛和复活节岛，印度洋上的留尼旺岛和毛里求斯，以及世界上大多数大洋上的大岛，都是由于地幔柱的存在而形成的。

Other islands, including Tahiti and Easter Island in the Pacific, Reunion and Mauritius in the Indian Ocean, and indeed most of the large islands in the world’s oceans, owe their existence to mantle plumes.

因此，海洋火山岛和它们的热点轨迹对地质学家来说特别有用，因为它们记录了固定火山源上板块过去的位置。

The oceanic volcanic islands and their hot-spot trails are thus especially useful for geologists because they record the past locations of the plate over a fixed source.

因此，它们允许重建海底扩张的过程，从而重建过去大陆和海洋盆地的地理。

They therefore permit the reconstruction of the process of seafloor spreading, and consequently of the geography of continents and of ocean basins in the past.

例如，考虑到太平洋板块的当前位置，夏威夷位于太平洋热点之上。

For example, given the current position of the Pacific Plate, Hawaii is above the Pacific Ocean hot spot.

因此，5000万年前的太平洋板块的位置可以通过移动它来确定，这样一个5000万年前的火山就坐落在热点地带的位置，也就是今天的夏威夷。

So the position of the Pacific Plate 50 million years ago can be determined by moving it such that a 50-million-year-old volcano in the hot-spot trail sits at the location of Hawaii today.

然而，由于海洋盆地在地质时间尺度上确实是短期的特征，通过沿着热点轨迹回溯来重建世界地理只在地质时期的最后5%左右起作用。

However, because the ocean basins really are short-lived features on geologic time scales, reconstructing the world’s geography by backtracking along the hot-spot trail works only for the last 5 percent or so of geologic time.

The author mentions “spreading ridges”, “subduction zones”, and “transform faults” in order to

The word “converge” in the passage is closest in meaning to

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

The word “instructive” in the passage is closest in meaning to

The word “eroded” in the passage is closest in meaning to

According to paragraph 3, what is the relationship between the scientific contributions of James Daly and Tuzo Wilson?

Why does the author provide the information that “the dating of lavas in the Hawaiian (and other) chains showed that their ages increase away from the presently active volcano”?

According to paragraph 4, which of the following is true of mantle plumes?

According to paragraph 5, volcanic islands help geologists to

What can be inferred about the Pacific Plate from paragraph 5?

The word “current” in the passage is closest in meaning to

According to paragraph 5, why are geologists unable to trace back the entire geologic history of continents from hot-spot trails?

Look at the four squares  that indicate where the following sentence could be added to the passage. This pattern remained unexplained for a long time.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

The Formation of Volcanic Islands Earth’s surface is not made up of a single sheet of rock that forms a crust but rather a number of “tectonic plates” that fit closely, like the pieces of a giant jigsaw puzzle. Some plates carry islands or continents; others form the seafloor. All are slowly moving because the plates float on a denser semiliquid mantle, the layer between the crust and Earth’s core. The plates have edges that are spreading ridges (where two plates are moving apart and new seafloor is being created), subduction zones (where two plates collide and one plunges beneath the other), or transform faults (where two plates neither converge nor diverge but merely move past one another). It is at the boundaries between plates that most of Earth’s volcanism and earthquake activity occur. Generally speaking, the interiors of plates are geologically uneventful. However, there are exceptions. A glance at a map of the Pacific Ocean reveals that there are many islands far out at sea that are actually volcanoes—many no longer active, some overgrown with coral—that originated from activity at points in the interior of the Pacific Plate that forms the Pacific seafloor. How can volcanic activity occur so far from a plate boundary? The Hawaiian Islands provide a very instructive answer.  Like many other island groups, they form a chain.  The Hawaiian Island Chain extends northwest from the island of Hawaii.  In the 1840s American geologist James Daly observed that the different Hawaiian Islands seem to share a similar geologic evolution but are progressively more eroded, and therefore probably older, toward the northwest.  Then in 1963, in the early days of the development of the theory of plate tectonics, Canadian geophysicist Tuzo Wilson realized that this age progression could result if the islands were formed on a surface plate moving over a fixed volcanic source in the interior. Wilson suggested that the long chain of volcanoes stretching northwest from Hawaii is simply the surface expression of a long-lived volcanic source located beneath the tectonic plate in the mantle. Today’s most northwestern island would have been the first to form. Then, as the plate moved slowly northwest, new volcanic islands would have formed as the plate moved over the volcanic source. The most recent island, Hawaii, would be at the end of the chain and is now over the volcanic source. Although this idea was not immediately accepted, the dating of lavas in the Hawaiian (and other) chains showed that their ages increase away from the presently active volcano, just as Daly had suggested. Wilson’s analysis of these data is now a central part of plate tectonics. Most volcanoes that occur in the interiors of plates are believed to be produced by mantle plumes, columns of molten rock that rise from deep within the mantle. A volcano remains an active “hot spot” as long as it is over the plume. The plumes apparently originate at great depths, perhaps as deep as the boundary between the core and the mantle, and many have been active for a very long time. The oldest volcanoes in the Hawaiian hot-spot trail have ages close to 80 million years. Other islands, including Tahiti and Easter Island in the Pacific, Reunion and Mauritius in the Indian Ocean, and indeed most of the large islands in the world’s oceans, owe their existence to mantle plumes. The oceanic volcanic islands and their hot-spot trails are thus especially useful for geologists because they record the past locations of the plate over a fixed source. They therefore permit the reconstruction of the process of seafloor spreading, and consequently of the geography of continents and of ocean basins in the past. For example, given the current position of the Pacific Plate, Hawaii is above the Pacific Ocean hot spot. So the position of the Pacific Plate 50 million years ago can be determined by moving it such that a 50-million-year-old volcano in the hot-spot trail sits at the location of Hawaii today. However, because the ocean basins really are short-lived features on geologic time scales, reconstructing the world’s geography by backtracking along the hot-spot trail works only for the last 5 percent or so of geologic time.