2011年考研英語特訓(xùn)：看閱讀背單詞(6)

　　Scatteredaround the globe are more than 100 small regions of isolated volcanic activity known to geologistsas hot spots. Unlike most of the world’s volcanoes, they are not always found at the boundaries of the great driftingplates that make up the earth’s surface; on the contrary, many of them lie deep in the interiorof 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 milestonesthat mark the passage of the plates.

　　That the plates are moving is not 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 remindersof where the two continents were once joined. The relative motion of the plates carrying these continentshas been constructed in detail, but the motion of one plate with respect to another cannot readilybe translated into motion with respect to the earth’s interior. It is not possible to determinewhether both continents are moving in opposite directions or whether one continent is stationary and the other is drifting away from it. Hot spots, anchored in the deeper layers of the earth, provide the measuring instruments needed to resolve the question. From an analysis of the hot spot population it appears that the African plate is stationary and that it has not moved during the past 30 million years.

　　The significanceof hot spots is not confined to their role as a frameof reference. It now appears that they also have an important influence on the geophysicalprocesses that propel the plates across the globe. When a continental plate come to rest over a hot spot, the material rising from deeper layer creates a broad dome. As the dome grows, it develops seed fissures(cracks); in at least a few cases the continent may break entirelyalong some of these fissures, so that the hot spot initiates the formation of a new ocean. Thus just as earlier theories have explained the mobilityof the continents, so hot spots may explain their mutability(inconstancy).

　　譯文

　　地球上散落分布著100多個(gè)互不相連的小火山活躍區(qū)，地質(zhì)學(xué)家稱之為熱點(diǎn)。與地球上大多數(shù)火山不同的是，它們并不總是在構(gòu)成地球表面的巨大漂流板塊之間的連接處上出現(xiàn);相反，許多熱點(diǎn)處于板塊較深的內(nèi)部。大多數(shù)熱點(diǎn)移動(dòng)極為緩慢，有些時(shí)候，板塊滑過這些熱點(diǎn)便留下了死火山的痕跡。熱點(diǎn)及其火山痕跡是板塊漂移的標(biāo)志。

　　現(xiàn)在對(duì)于板塊漂移這一理論是毋庸置疑的。例如，由于有新的物質(zhì)注入二者之間的海底，非洲和南美洲距離越來越遠(yuǎn)。即使跨越海洋，但是由于相互吻合的海岸線和某些可樂了海洋類似的地質(zhì)特征都能使人會(huì)想到整個(gè)兩個(gè)大陸曾經(jīng)是連在一起的。對(duì)于這些大陸的板塊的相對(duì)運(yùn)動(dòng)已經(jīng)能夠被詳細(xì)地解釋出來，但是以地球內(nèi)部為參照物，不能很好地說明一個(gè)板塊相對(duì)于另一個(gè)板塊的相對(duì)運(yùn)動(dòng)之間的關(guān)系。人們不能確定是兩個(gè)大陸都朝相反的方向運(yùn)動(dòng)漂移而去，還是一個(gè)大陸靜止不動(dòng)另一個(gè)大陸從他身邊漂移而走。處于地球更深層的熱點(diǎn)提供了解決該問題的測(cè)量儀器。通過對(duì)熱點(diǎn)區(qū)域的研究情況發(fā)現(xiàn)，非洲板塊似乎是靜止不動(dòng)的，至少在過去的3000萬年里沒有移動(dòng)過。

　　熱點(diǎn)的重要性不僅只是局限于其作為參照系統(tǒng)所表現(xiàn)的作用�，F(xiàn)在看來，熱點(diǎn)還對(duì)推動(dòng)板塊在地球表面漂移這一地球物理過程有重大影響。當(dāng)大陸板塊漂移到熱點(diǎn)上方時(shí)，來自地球深層的物質(zhì)便形成了巨大的拱形隆起物。隨著該拱形的增長，板塊出現(xiàn)深深的裂縫。至少有些情況下，大陸可能會(huì)沿著其中的某些裂縫完全裂開，該熱點(diǎn)就引發(fā)了一個(gè)新的海洋的形成。因此，正如早期的理論解釋了大陸的漂移性一樣，熱點(diǎn)理論或許能夠解釋大陸板塊的易變性。