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.
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。
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