浅说板块构造论

The idea that our planet's comtinents drift around the globe,periodically glomming together and breaking apart,is at least 200 years old.But most geologists didn't believe it until the 1960's,when mounting evidence made it clear that the Earth's crust is broken up into fragments,and that those fragments,called tectonic plates,are moving.

地球上的板块漂浮在全球各地,板块间会发生聚合和张裂,这种说法由来已月00多年,但在20世纪60年代之前,许多地质学家并不认同这种说法,直到越来越多的证据表明,地球的地壳会分裂成碎片,而这些被称为构造板块的碎片是会移动的。
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And these days we directly track that motion-with millimeter precision-from space.The common,simplified explanation for why tectonic plates are moving is that they're carried along on currents in the upper mantle,the slowly flowing layer of rock just below Earth's crust.Converging currents drive plates into each other,diverging currents pull them apart.

如今我们能够以毫米级的精确度,从太空直接观察到这种现象,目前普遍认为,造成构造板块移动的原因,简单说来就是板块随上地幔热对流而动,地幔岩流层就位于地壳下方,汇聚的对流导致板块分裂,分散的对流则会聚合板块。
This is mostly true;hot mantle rock rises from the core and moves along under the crust until it grows cool and heavy and sinks back down again.But the plates aren't just passively riding these conveyer-belt-like currents around like a bunch of suitcases at the baggage claim.They can't be,because some of the plates are moving faster than the currents underneath them.
这基本是对的,热的地幔岩从地核处上升至地壳,直到慢慢冷却变重沉积回去,但是板块不会像行李认领处,传送带上的箱包那般顺从,它们做不到,国为有些板块的移动速度比下层的岩石更快。
For example,the Nazca plate-a chunk of ocean crust off the west coast of South America-is cruising eastward at about 10cm per year,while the mantle underneath it oozes along at just five.Neither tectonic plates nor luggage can move faster than the belt they're riding on unless something else is helping to push or pull them along.
例如,位于南美洲西海岸的大洋板块----纳斯卡板块,它正以每年10厘米的速度向东移动,而其下方的地幔每年只移动5厘米,无论是构造板块还是行李箱,都不可能动的比传送带快,除非还存在其他对它们产生推拉力的东西。
And some of Earth's plates,it turns out,are pulling themselves.When an ocean plate collides with another ocean plate or a plate bearing the thick crust of continental landmasses,the thinner of the two plates bends and slides under the other.As the edge of the seafloor sinks into the mantle,it pulls on the plate behind it,they same way a chain dangling further and further off a table will eventually start to slide.
事实证明,有些地球板块会对自身产生牵引力,当一片大洋板块与另一块大洋板块,或是一片承载着厚重岩层的大陆板块相撞,那么薄的那片板块会发生弯曲滑入另一片板块下方,随着海底的边缘陷入地幔,这会拉动位于其上的板块,就像桌边的锁链一点一点的下坠,最后总会掉下去。
The bigger the sunken portion of the plate becomes,the harder it pulls and the faster the remaining plate behind it moves.You can find where this is happening by looking at google earth-the incredibly deep,narrow ocean trenches visible off the coasts of some continents and island chains mark the creases formed as ocean crust plunges downward,bending the edge of its neighbor in the process.
板块下沉的面积越大,产生的拉力就越大,余下板块运动速度也越快,你可以通过谷歌地图找出发生过下沉的地方,那些远离大陆海岸,极深的狭窄海沟和岛链,标示着大洋板块下沉形成的褶皱,那是相邻板块在碰撞过程中弯曲而形成的。
What's more,helping to drive convection in the mantle beneath them.Sunken slabs of ocean crust block flowing rock from moving further sideways,forcing it to turn downward and sink.
此外,有助于它们下方地幔的热流运动,沉没的大洋板块阻止岩流向更深处移动,迫使它向下沉。
Eventually those slabs get too heavy and break off,plunging slowly toward the core and creating a suction force that pulls mantle material along behind it.So,in some ways,seafloor crust really is more like part of the conveyor belt than something riding on top of it.The continents,on the other hand,are baggage.
最后,这些板块由于太重而断裂,慢慢插入地核,并且形成牵引力拉动后方的地幔物质,所以,从某个角度来说,与行李相比,海底地壳其实更像是传送带的一部份,换句话说，大陆就是行李。

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