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 semi-liquid 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at a map of the Pacific Ocean reveals that there are many islands far out at sea that are actually volcanoes----many no longer active, some overgrown with coral----that originated from activity at points in the interior of the Pacific Plate that forms the Pacific seafloor.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 Islands Chain extends northwest from the island of Hawaii. In the 1840s American geologist James Daly observed that the different Hawaii islands seem to share a similar geologic evolution but are progressively more eroded, and therefore probable 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 northwest island would have been the first to form. They as the plate moved slowly northwest, new volcanic islands would have forms 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 Hawaii (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 Hawaii hot-spot trail have ages close to 80 million years. Other islands, including Tahiti and Easter Islands in the pacific, Reunion and Mauritius in the India 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 geologist 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-oil 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 times scale, reconstruction the world’s geography by backtracking along the hot-spot trail works only for the last 5 percent or so of geologic time.
Paragraph 1: 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 gain jigsaw puzzle. Some plates carry islands or continents, others form the seafloor. All are slowly moving because the plates float on a denser sem-iliquid 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.
1.The author mentions “spreading ridges”, “subduction zones”, and “transform faults” in order to
O illustrate that the boundaries of tectonic plates are neat, thin lines
O explain why some tectonic plates carry islands or continents while others form the seafloor
O explain the complex nature of the edges of tectonic plates
O provide examples of areas of tectonic plates where little geologic action occurs
2. The word “converge” in the passage is closest in meaning to
O expand
O form
O rise
O move closer
Paragraph 2: Generally speaking, the interiors of plates are geologically uneventful. However, there are exceptions. A glance at a ma 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.
3.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
O Volcanic activity is responsible for the formation of the Pacific seafloor in the interior of the Pacific Plate.
O Many volcanoes in the Pacific Ocean are no longer active and have become islands that support coral.
O There are many islands in the Pacific Ocean that originated as volcanoes in the interior of the Pacific Plate.
O The map of the Pacific Ocean reveals fewer volcanic islands than there truly are because many are no longer active and some are completely overgrown with coral.
Paragraph 3: 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 Islands Chain extends northwest from the island of Hawaii. In the 1840s American geologist James Daly observed that the different Hawaii islands seem to share a similar geologic evolution but are progressively more eroded, and therefore probable 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 northwest island would have been the first to form. They as the plate moved slowly northwest, new volcanic islands would have forms 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.
4. The word “instructive” in the passage is closest in meaning to
O clear
O detailed
O informative
O familiar
5. The word “eroded” in the passage is closest in meaning to
O worm down
O scattered
O developed
O deserted
6.In paragraph 3, what is the relationship between the scientific contribution of James Daly and Tuzo Wilson?
O Wilson provided an explanation for the observations made by Daly.
O Wilson challenged the theory proposed by Daly.
O Wilson found numerous examples of island chains that supported Daly’s theory.
O Wilson popularized the explanation of volcanic island formation formulated by Daly.
Paragraph 4: Although this idea was not immediately accepted, the dating of lavas in the Hawaii (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 Hawaii hot-spot trail have ages close to 80 million years. Other islands, including Tahiti and Easter Islands in the pacific, Reunion and Mauritius in the India Ocean, and indeed most of the large islands in the world’s oceans, owe their existence to mantle plumes.
7.Why does the author provide the information that “the dating of lavas in the Hawaii (and other) chains showed that their ages increase away from the presently active volcano”?
O To point out differences between the Hawaii island chain and other volcanic island chains
O To question the idea that all the islands in an island chain have been formed by volcanic activity
O To explain why Wilson hypothesis was initially difficult to accept
O To provide evidence in support of Daly’s and Wilson’s ideas about how the Hawaii islands were formed
8.According to paragraph 4, which of the following is true of mantle plumes
O They exist close to the surface of tectonic plates.
O They cause most of the volcanic activity that occurs in the interiors of plates.
O They are rarely active for long period of time.
O They get increasingly older away from the present hot spots.
Paragraph 5: The oceanic volcanic islands and their hot-spot trails are thus especially useful for geologist 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-oil 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 times scale, reconstruction the world’s geography by backtracking along the hot-spot trail works only for the last 5 percent or so of geologic time.
9.According to paragraph 5, volcanic islands help geologists to
O reconstruct past geography
O detect changes in mantle plumes
O measure the rigidity of tectonic plates
O explain why the seafloor spreads
10.What can be inferred about the Pacific Plate from paragraph 5?
O The hot spots on the Pacific Plate are much older than the ones located on the other tectonic plates.
O Most of the volcanic sources beneath the Pacific Plate have become extinct.
O The Pacific Plate has moved a distance equal to the length of the Hawaiian Island chain in the past 80 million years.
O The Pacific Plate is located above fewer mantle plumes than other plates are.
11. The word “current” in the passage is closest in meaning to
O original
O ideal
O relative
O present
12.According to paragraph 5, why are geologists unable to trace back the entire geologic of continents from hot-spot trails?
O Hot spots have existed for only about 5 percent of geologic time.
O Hawaii did not exist 50 millions years ago.
O Oceanic basins that contained old hot-spot trails disappeared a long time ago.
O Hot-spot trails can be reconstructed only for island chains.
Paragraph 3: 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 Islands Chain extends northwest from the island of Hawaii. ■In the 1840s American geologist James Daly observed that the different Hawaii islands seem to share a similar geologic evolution but are progressively more eroded, and therefore probable 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 northwest island would have been the first to form. They as the plate moved slowly northwest, new volcanic islands would have forms 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.
13.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?
14 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.
Although volcanic activity is concentrated on the edge of tectonic plates, such activity can occur in the interiors of plates as well.
Answer Choices
●
●
●
O Our understanding of islands comes from Daly’s and Wilson’s observations of the Hawaiian Islands, which was later confirmed by plate-tectonic theory.
O The hot-spot trails formed by volcanic island chains indicate the positions of tectonic plates as for back as the present ocean basins have existed.
O Whereas volcanic islands formed by mantle plumes are typically small, most of the world’s largest islands are formed at the edges of tectonic plates.
O It has only recently been discovered that tectonic plates are closely fitting rather than loosely constructed, as geologist previously believed.
O Volcanic island chains such as the Hawaiian Islands form in the interior of a tectonic plate as the plate moves over a fixed volcanic source in the mantle.
O The Pacific Plate has existed for as long as the Hawaiian Islands have existed, namely for more than 80 million years.
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14. Our understanding of islands comes…
Whereas volcanic islands…
It has only recently been…
地球的外殼并不是由單塊巖石形成的，而是許多的“構(gòu)造板塊”嚴密的組合在一起的，就像是一個巨大的拼圖。一些板塊承載著島嶼或是大陸，其它的則形成海底。所有板塊都在緩慢移動，因為它們都漂浮在密度更大的半液態(tài)的介于地殼和地核之間的地幔上。板塊的邊緣是擴張脊（兩個板塊分離，新的海底形成的地方），俯沖帶（兩板塊碰撞，一個傾入到另一個下面），或者是形成斷層（兩板塊既不聚集也不分散，但只是互相錯位）。板塊邊界是地球上的火山和地震的高發(fā)地。
一般地，板塊內(nèi)部在地質(zhì)上是平靜的，但也有例外。掃一眼太平洋的地圖就知道那里有許多在大海深處的島嶼，它們其實都是火山，其中有許多已經(jīng)不活動了，一些長滿了珊瑚。這些火山都起源于當(dāng)時太平洋板塊內(nèi)部一些部位在形成太平洋海底時的地質(zhì)活動。
為什么火山活動發(fā)生在離板塊邊緣這么遠的地方呢？夏威夷群島提供了一個非常有啟發(fā)性的答案。就像其它的群島一樣，它們形成了一個島鏈。夏威夷群島鏈從夏威夷島向西北擴張。在十八世紀40年代，地質(zhì)學(xué)家James Daly觀察到不同的夏威夷島嶼看起來經(jīng)歷了相似的演變過程，但它們所受腐蝕一個比一個嚴重，所以越往西北方向的島嶼形成時間可能越早。1963年，在大陸板塊理論的早期，加拿大的地質(zhì)學(xué)家Tuzo Wilson意識到島嶼年齡的增加可能是因為這些島嶼是板塊表面從一個板塊內(nèi)部的固定火山源上方移動的結(jié)果。Wilson解釋說，夏威夷向西北延伸的火山長鏈只是一個長期存于板塊下、地幔中的火山源在板塊表面的表現(xiàn)�，F(xiàn)今最靠西北的島嶼可能是最先形成的。它們隨著板塊向西北移動。新的火山會隨著板塊的移動在火山源處形成。最年輕的島嶼，夏威夷島，應(yīng)該是在島鏈的末端，現(xiàn)在應(yīng)該在火山源上。
雖然這個理論并沒有被很快接受，夏威夷和其它群島巖漿的年齡測試表明了它們的年齡都從活躍的火山開始依次增加，正如Daly所說。Wilson對數(shù)據(jù)的分析已經(jīng)成為了板塊構(gòu)造論的核心部分。大多的發(fā)生在板塊內(nèi)部的火山爆發(fā)都是由地幔柱造成的；地幔柱是從地幔深處涌出的熔巖柱體。只要火山在一個地幔柱上面，它就是一個活動的“熱點”。地幔柱很顯然是起源于很深的地方，很可能位于地核和地幔的交界處，并且已經(jīng)活躍了很久。由夏威夷熱點形成的最老的火山已經(jīng)有近8千萬年的時間了。其它的島嶼，包括太平洋的塔希提島和東部群島，印度洋留尼汪島和毛里求斯群島，實際上，多數(shù)世界上大洋中大島都是由地幔柱的擴展形成的。
海洋火山島和它們的熱點軌跡對于地質(zhì)學(xué)家尤其有用，因為它們記錄了過去的板塊在固定火山源上方的位置。他們因此可以重現(xiàn)海底擴張的過程，以及大陸和大洋盆地過去的地理位置發(fā)展過程。比如，根據(jù)太平洋板塊現(xiàn)在的位置，夏威夷島在太平洋熱點上面。所以太平洋板塊5千萬年前的位置可以通過移動太平洋板塊使得一座有5五千萬年歷史的島嶼位于夏威夷島現(xiàn)在所在的熱點上以獲得。但是，由于海洋盆地在地質(zhì)年代上是相對短命的，用熱點追蹤的方法重建世界的地形只適用于最近的百分之五左右的地質(zhì)時間。
