新GRE考试辅导：阅难难句的攻克（20）

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37.The best evidence for the layered-mantle thesis is thewell-established fact that volcanic rocks found on oceanicislands，islands believed to result from mantle plumes arising from thelower mantle，are composed of material fundamentally different from thatof the midocean ridge system， whose source，most　geologists contend，isthe upper mantle.  
1 B1 |; p3 v6 H! l3 [' E1 @　　对于地幔分层论点来说，最好的证据乃这样一个确认的事实，即在那些海洋岛屿——这些岛屿据信是源于由下层地幔升上来的地幔柱状溶岩流(mantleplume)——上发现的火山岩石，是由与海洋中部山脊系统的物质根本不同的物质构成的，而这一海洋中部山脊系统的成因，大多数地质学家论辩道，为上部地幔。
" @% ~1 L$ r, i! c! w38.Some geologists，however，on the basis of observations concerningmantle　xenoliths，argue that the mantle is　not layered，but thatheterogeneity is created by fluids rich in “incompatible elements”(elements tending toward　liquid rather than solid state)percolatingupward and transforming　portions of the uppermantle　irregularly，according to the vagaries of the fluids’ pathways.
　　但是，某些地质学家，以对地幔捕虏岩体(xenolith)所作的观察为依据，指出地幔并非是分层排列的，相反，地幔的异质性是由那些富含“不相容成分”的流质构成的，这些成分趋向于流体而非固体的状态，自下而上渗透扩散，并依照这些流质流向的任意性，不规则地将上部地幔的某些部分予以改变。