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  3. Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots. Unlik

Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots. Unlik

admin2016-11-21  61
问题     Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots. Unlike most of the world’s volcanoes, they are not always found at the boundaries of the great drifting plates that make up the earth’s surface. On the contrary, many of them lie deep in the interior of a plate. Most of the hot spots move only slowly, and in some cases the movement of the plates past them has left trails of dead volcanoes. The hot spots and their volcanic trails are milestones that mark the passage of the plates.
    That the plates are moving is now beyond dispute. Africa and South America, for example, are moving away from each other as new material is injected into the sea floor between them. The complementary coastlines and certain geological features that seem to span the ocean are reminders of where the two continents were once joined. The relative motion of the plates carrying these continents has been constructed in detail, but the motion of one plate with respect to another cannot readily be translated into motion with respect to the earth’s interior. It is not possible to determine whether both continents are moving in opposite directions or whether one ocean is stationary and the other is drifting away from it. Hot spots, anchored in the deeper layer of the earth, provide the measuring instruments needed to resolve the question. From an analysis of the hot-spot population it appears that it has not moved during the 30 million years.
    The significance of hot spots is not confined to their role as a frame of reference. It now appears that they also have an important influence on the geophysical processes that propel the plates across the globe. When a continental plate comes to rest over a hot spot, the material rising from deeper layers creates a broad dome. As the dome grows, it develops deep fissures(cracks): in at least a few cases the continent may break entirely along some of these fissures, so that the hot spot initiates the formation of new ocean. Thus just as earlier theories have explained the mobility of the continents, so hot spots may explain the mobility of the continents, and their mutability(inconstancy).
The hot-spot theory may prove useful in explaining______.
选项 A、the structure of the African plate
B、the revival of dead volcanoes
C、the mobility of the continents
D、the formation of new oceans
答案D
解析 事实细节题。从最后一段可以看出，不稳定地带的意义并不仅仅局限于作为一种参照，它们对推动板块移动的地质物理过程似乎也有重要影响。当大陆板块移动到不稳定地带之上时，地下更深层产生的物质会形成一个巨大圆顶。圆顶在增长过程中产生裂缝，有时大陆沿着一些裂缝完全断裂，导致新海洋的形成。可见D为答案。A和B文中并未提及，而“不稳定地带”理论无法解释C。
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