gwd7-q23

Nickyl90

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 surfaceplate. 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

A   a curved outline
B   constituent volcanoes that differ from each other in age
C   occurrence near a plate boundary where one plate bends under another
D   appearance near many other volcanic chains
         

E   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

lilingfeng

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。

xiaoxiangxixi

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

xiaotangyu

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。