板块结构与海床扩展

1、板块结构与海床扩展（Plate Tectonicsand Sea板块结构与海床扩展(Plate Tectonics and Sea-floor Spreading)板块结构与海床扩展(Plate Tectonics and Sea-floor Spreading) comparatively rigid outer layer of the earth that includes all the crustand part of the underlying mantle. the lithosphere is divided into a fewdozen plates of various

2、 sizes and shapes, in general theplates are inmotion with respect to one another. a mid-ocean ridge isa boundarybetween plates where new lithospheric material is injected from belows. asthe plates diverge from a mid-ocean ridge they slide on amore yieldinglayer at the base of the lithosphere.since t

3、he size of the earth is essentially constant, new lithosphere canbe created at the mid-ocean ridges only if an equalamount of lithosphericmaterialis consumedelsewhere.the site of thisdestruction is anotherkind of plate boundary:a subduction zone. there oneplate dives under theedge of another and is

4、reincorporated into the mantle. both kinds of plateboundary are associated with fault systems, earthquakesand volcanism, butthe kinds of geologic activity observed at the two boundaries are quitedifferent.the idea of sea-floor spreading actually preceded the theory of platetectonics. in its original

5、 version, in the early 1960s, it described thecreation and destruction of the ocean floor, but it did notspecify rigidlithospheric plates. the hypothesis was substantiated soon afterward by thediscovery that periodic reversals of the earths magneticfield arerecorded in the oceanic crust. as magma ri

6、ses under the mid-oceanridge, ferromagnetic minerals in the magma become magnetized in thedirection of the geomagnetic field. when the magma cools and solidifies,the direction and the polarity of the field are preserved inthe magnetizedvolcanic rock. reversals of the field give rise to a series of m

7、agneticstripes running parallel to the axis of the rift. the oceaniccrust thusserves as a magnetic tape recording of the history of the geomagnetic fieldthat can be dated independently; the width of the stripes indicates therate of the sea-floor spreading.板块结构与海床扩展英语译文：板块结构理论描述岩石圈的运动。岩石圈是相对坚硬的地球外层，包

8、括全部地壳和部分地幔。岩石圈被划分为几十个大小不同形状各异的板块，一般而言这 些板块都处于相对 运动之中。一道中海脊是板块之间的边界，在那 里新的岩石圈的物质从下部注入。当板块 从中海脊脱离时，它们滑向在岩石圈基部较易变形的地 层上。因为地球的大小本质上是不变的，只有同等数量的岩石圈物质在其它地方被吞没，新的岩石圈才能生成。销毁旧岩石圈的地方形成另外一种板块边界：一块潜没的区域。在这里，一块板块潜没到另一板块的 边缘之下并结合入地幔之中。两种板块边界均与地层系统、地震以及火山活动有关，但在两 种边界处观察到的诸般地质活动却迥然不同。海床扩展说实际上早于板块结构理论。在20世纪60年代它的理论雏形中，描述了海底的生成和毁灭， 但没有详细介绍坚硬的岩石圈 板块。这个假定不久之后为发现所证 实。该发现表明地球磁场周期性的逆转被记录在海洋地壳中。当岩浆从中海脊下涌起的时候，岩