5.16大陆边缘
Section outline
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Can plate tectonics explain the differences in these beaches?
::板块构造能解释这些海滩的差别吗?Plate tectonics explains why some beaches have lots of cliffs and some do not. A beach with lots of cliffs is near a plate boundary . A gentle beach is not. There are exceptions to this rule, but it works in some cases.
::板块构造解释了为什么一些海滩有许多悬崖,有些则没有。 有很多悬崖的海滩在板块边界附近。 温和的海滩不是。 这条规则有例外,但在某些情况下是有效的。Continental Margins
::大陆边缘Think of a continent , like North America. Surrounding the continent are continental margins . Continental crust grades into oceanic crust at continental margins. Continental margins are under water . Almost all of North America sits on the North American Plate ( Figure ). Both sides of the continent have continental margins, but each is very different. One continental margin of North America is an active margin . The other is a passive margin . Can you guess which is which?
::想象一个大陆, 像北美。 环绕这个大陆的大陆是大陆边。 大陆地壳的等级是大陆边的海洋地壳。 大陆边处于水下。 几乎所有的北美都坐在北美板块上( 图表 ) 。 非洲大陆的两边都有大陆边, 但每个边都有非常不同的。 北美的一个大陆边是一个积极的边。 另一个是被动边。 你能猜出哪个是哪个吗?The North American plate and the plates that surround it. Active Margins
::活动边界If a continental margin is near a plate boundary, it is an active margin . The continental margin of western North America is near a set of plate boundaries. There are convergent boundaries, like where there is subduction off of the Pacific Northwest. There is a transform boundary, the San Andreas . The small amount of the North American continent that is not on the North American Plate is across the San Andreas Fault. It is on the Pacific Plate. Western North America has a lot of and . Mountains line the region. California, with its volcanoes and earthquakes, is an important part of this active margin ( Figure ).
::如果大陆边接近板块边界,就是一个活跃的边距。北美西部的大陆边接近一组板块边界。有一些汇合的边界,如从西北太平洋下潜的地方。有一个变形的边界,即圣安德烈亚斯。北美大陆中不位于北美板块上的一小部分是在圣安德烈亚斯断层上。它是在太平洋板块上。西北美有大量的火山和地震,是这个区域的重要部分(图)。Big Sur, in central California, has beautiful cliff-lined beaches. Passive Margins
::被动边缘On the eastern edge of North America, the plate smoothly transitions from continental to oceanic lithosphere . The far eastern edge of the North American Plate is the mid-Atlantic Ridge. There is no plate boundary near the coast. This means that the eastern coast of North America is on a passive margin ( Figure ).
::在北美东部边缘,板块顺利地从大陆向海洋平流层过渡。北美板块的远东边缘是中大西洋海脊。在海岸附近没有板块边界。这意味着北美东部海岸处于被动边缘(图 ) 。There are no volcanoes and very few earthquakes on the eastern edge of North America. However, there are mountains. Mountains on a passive continental margin formed in the distant past, when the region was geologically active. For example, the Appalachian mountains formed around 300 million years ago when Pangea was coming together.
::北美东部边缘没有火山,地震也很少。然而,有山脉。山在遥远的过去形成的一个被动的大陆边缘山脉,当时该地区地质活跃。例如,3亿年前,当潘热亚聚集在一起时,阿巴拉契亚山脉就形成了。The eastern U.S. is a passive margin. Daytona Beach in Florida is flat and sandy, typical of a passive margin. Summary
::摘要- Continental margins can be active or passive depending on whether they are near a plate boundary.
::大陆边的主动或被动程度取决于它们是否接近板块边界。
- Volcanoes and earthquakes are common at active margins. Active margins are near plate boundaries.
::火山和地震在活动边缘很常见,活动边缘靠近板块边界。
- Passive margins are passive. They have little or no geological activity.
::被动边缘是被动的,它们几乎没有或根本没有地质活动。
Review
::回顾- Describe the continental margin of Western North America.
::描述北美西部大陆边。
- Describe the continental margin of Eastern North America.
::描述北美东部大陆边。
- Why are there mountain ranges at passive margins?
::为什么有山脉处于被动边缘?
- Continental margins can be active or passive depending on whether they are near a plate boundary.
