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GRE阅读题目解析:地幔的结构

2017-03-30 08:39:00来源：新东方在线整理

　　【GRE阅读题目解析:地幔的结构】GRE考试考什么？GRE阅读是重点。新东方在线GRE频道为大家带来GRE阅读题目解析:地幔的结构，答案见下一页，希望对大家GRE备考有所帮助。更多精彩尽请关注新东方在线GRE频道!

　　查看全部：GRE阅读答案解析(汇总)

　　GRE阅读题目解析:地幔的结构

　　P4

　　Geologists have long known that the Earth‘s mantle is heterogeneous, but its spatial arrangement remains unresolved — is the mantle essentially layered or irregularly heterogeneous? The best evidence for the layered-mantle thesis is the well-established fact that volcanic rocks found on oceanic islands, islands believed to result from mantle plumes arising from the lower mantle, are composed of material fundamentally different from that of the midocean ridge system, whose source, most geologists contend, is the upper mantle.

　　Some geologists, however, on the basis of observations concerning mantle xenoliths, argue that the mantle is not layered, but that heterogeneity is created by fluids rich in "incompatible elements" (elements tending toward liquid rather than solid state) percolating upward and transforming portions of the upper mantle irregularly, according to the vagaries of the fluids‘ pathways. We believe, perhaps unimaginatively, that this debate can be resolved through further study, and that the underexplored midocean ridge system is the key. (157 words)

　　10. According to the passage, it is believed that oceanic islands are formed from

　　(A) the same material as mantle xenoliths

　　(B) the same material as the midocean ridge system

　　(C) volcanic rocks from the upper mantle

　　(D) incompatible elements percolating up from the lower mantle

　　(E) mantle plumes arising from the lower mantle

　　For the following question, consider each of the choices separately and select all that apply

　　11. It can be inferred from the passage that the supporters of the "layered-mantle" theory believe which of the following?

　　□A The volcanic rocks on oceanic islands are composed of material derived from the lower part of the mantle.

　　□B The materials of which volcanic rocks on oceanic islands and midocean ridges are composed are typical of the layers from which they are thought to originate.

　　□C The differences in composition between volcanic rocks on oceanic islands and the midocean ridges are a result of different concentrations of incompatible elements.

　　12. In the context of the passage, "unimaginatively" is closest in meaning to

　　(A) pedestrian

　　(B) controversial

　　(C) unrealistic

　　(D) novel

　　(E) paradoxical

　　点击下一页查看答案：

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