gwd7-q23看了讨论贴还是不明白，请教NN

yuanzi15

Q22 to Q25:

Earth’s surface consists of rigid
            

plates that are constantly shifting and

jostling one another. Plate movements

Line are the surface expressions of motions

(5) in the mantle—the thick shell of rock

that lies between Earth’s crust and its

metallic core. Although the hot rock of

the mantle is a solid, under the tre-

mendous pressure of the crust and

(10) overlying rock of the mantle, it flows like

a viscous liquid. The mantle’s motions,

analogous to those in a pot of boiling

water, cool the mantle by carrying hot

material to the surface and returning

(15) cooler material to the depths. When

the edge of one plate bends under

another and its cooler material is con-

sumed in the mantle, volcanic activity

occurs as molten lava rises from the

(20) downgoing plate and erupts through the

overlying one.

Most volcanoes occur at plate

boundaries. However, certain “mis-

placed” volcanoes far from plate

(25) edges result from a second, indepen-

dent mechanism that cools the deep

interior of Earth. Because of its prox-

imity to Earth’s core, the rock at the

base of the mantle is much hotter than

(30) rock in the upper mantle. The hotter the

mantle rock is, the less it resists flow-

ing. Reservoirs of this hot rock collect

in the base of the mantle. When a

reservoir is sufficiently large, a sphere

(35) of this hot rock forces its way up

through the upper mantle to Earth’s

surface, creating a broad bulge in the

topography. The “mantle plume” thus

formed, once established, continues to

(40) channel hot material from the mantle

base until the reservoir is emptied.

The surface mark of an established

plume is a hot spot—an isolated

region of volcanoes and uplifted terrain

(45) located far from the edge of a surface

plate. Because the source of a hot

spot remains fixed while a surface

plate moves over it, over a long period

of time an active plume creates a chain

(50) of volcanoes or volcanic islands, a

track marking the position of the plume

relative to the moving plate. The natural

history of the Hawaiian island chain

clearly shows the movement of the

Pacific plate over a fixed plume.

Q23:

It can be inferred from the passage that a chain of volcanoes created by a mantle plume would most likely be characterized by

1. a curved outline
           
2. constituent volcanoes that differ from each other in age
           
3. occurrence near a plate boundary where one plate bends under another
           
4. appearance near many other volcanic chains
           
5. rocks with a wide range of chemical composition

还是不明白大家是怎么infer出B的，请NN指点

yuanzi15

up

yuanzi15

有人么？

yuanzi15

请教好心人，哭求~

yuanzi15

有人么？

yuanzi15

没人么？

yuanzi15

up

hksdhfweiuwh

用排除法很快。文章讲了两种火山，一种是板块碰撞引起的，一种是从地心直接喷发的，前者发生在板块交接处，后者远离板块交接处。AC讲的是板块碰撞火山的特点，错。DE根本没有被提及，所以选B

B对是因为这种火山是由一个口喷射从地心发出的岩浆形成的，虽然喷射地不变，但是地球板块会缓慢移动，因此形成一连串火山，所以这一连串火山自然是不同年龄的了。

jiaming12

解释的很清楚 谢谢 不过我选的是D 考虑的是：既然因为地球板块在移动 那么这种由地心引发的火山爆发会形成chain的火山群

liushangruc

LZ在题中不是已经用蓝色标出来了吗？
就是说火山喷发源头地点没有变，而地壳板块移动造成了在板块上的一连串火山，既然板块移动很慢，那么这些先后形成的火山肯定寿命不同。