What are Crustal Plates?

Geology, the study of our planet Earth, is essentially a science of keen observation of all the natural processes of the planet that go on around us all the time. Consequently, a great deal is known about the earth, although, of course, there is still a great deal to be learned. Let’s know detail about what are crustal plates.

You have already  seen, for example, what  makes the rain  fall,  how rivers  form,  how volcanoes  work,  even that whole continents  are able to  move, and so on. What has been needed, however, is an idea, a theory, which would knit together all that is known about the separate processes into one unified whole.

This would be a theory to explain how continents drift, why earthquakes occur only in certain parts of the Earth, why there are deep ocean trenches in some areas or oceanic ridges in others.

Today we seem to have such a theory explaining all, or most of what has been puzzling the experts for many years. This is the all-embracing theory of plate tectonics. The word ‘tectonics’ comes from the Greek tecton, a builder. In other words, tectonics refers to building and structure, in this case of the Earth itself. Thus, the idea of plate tectonics suggests that the surface of the Earth is made up of a number of rigid plates comprising the thickness of the crust and the upper part of the mantle.

The plates are free to move, and indeed are doing so today, floating on the plastic substance of the deeper layer of the Earth’s mantle, called the asthenosphere. They may well be kept in motion by the convection currents that have been mentioned before.

What are crustal plates

This is a simple map of the major crustal plates of the world and the directions in which they are moving at present.

The important point  to remember  is that the  plates are solid  and rigid  so that  almost all the  activities  that we  have mentioned such as  volcanoes  and earthquakes, are to be found  associated with the edges of these  plates, or the plate  margins, as they are more usually called.

What are crustal plates

This block of the Earth’s crust and mantle shows how the movements of plates, the formation of ocean ridges, mountain buildings, etc., are related.

There are three main types of margin. The plates may just slide past each other, such as the San Andreas Fault in California, and this is called a conservative margin. The mid-oceanic ridges, where mantle material is welling up from the crust, are known as constructive margins.

In other  places, such as the  west coast of South  America, where the  island  arcs occur that you have  already learned about, one crustal  plate  is slipping  beneath the other  at a destructive  margin.

The deep ocean trenches, such as the Marianas Trench, are to be found here, where the sea floor is pulled down. Earthquake activity is often concentrated in a zone known as the Benioff zone in these areas.

What are crustal plates

The Earth’s magnetism may be ‘frozen’ into cooling igneous rocks. Its direction changes periodically and these stripes record the changes progressively – older rocks moving away from the mid-ocean ridge. This is more evidence for sea-floor spreading.

You can see, then, that in one unifying idea, the Earth’s activities can be viewed as a whole, rather than as a number of isolated processes.

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