1、板塊結構與海床擴展（Plate Tectonicsand Sea板塊結構與海床擴展(Plate Tectonics and Sea-floor Spreading)板塊結構與海床擴展(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.板塊結構與海床擴展英語譯文：板塊結構理論描述巖石圈的運動。巖石圈是相對堅硬的地球外層，包

8、括全部地殼和部分地幔。巖石圈被劃分為幾十個大小不同形狀各異的板塊，一般而言這 些板塊都處于相對 運動之中。一道中海脊是板塊之間的邊界，在那 里新的巖石圈的物質從下部注入。當板塊 從中海脊脫離時，它們滑向在巖石圈基部較易變形的地 層上。因為地球的大小本質上是不變的，只有同等數量的巖石圈物質在其它地方被吞沒，新的巖石圈才能生成。銷毀舊巖石圈的地方形成另外一種板塊邊界：一塊潛沒的區域。在這里，一塊板塊潛沒到另一板塊的 邊緣之下并結合入地幔之中。兩種板塊邊界均與地層系統、地震以及火山活動有關，但在兩 種邊界處觀察到的諸般地質活動卻迥然不同。海床擴展說實際上早于板塊結構理論。在20世紀60年代它的理論雛形中，描述了海底的生成和毀滅， 但沒有詳細介紹堅硬的巖石圈 板塊。這個假定不久之后為發現所證 實。該發現表明地球磁場周期性的逆轉被記錄在海洋地殼中。當巖漿從中海脊下涌起的時候，巖