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Tectonic Plates—What are the lithospheric plates? (Educational)

The cool, rigid, outer layer of the earth,
the lithosphere, is broken into massive plates. There are about a dozen major plates and many
smaller plates in continuous motion as they collide with, slide under, or move past
each other in a process known as plate tectonics. A plate may be entirely oceanic lithosphere, like the Pacific Plate, or, like the NorthAmerican plate can be part oceanic and part continental lithosphere. We will return to lithosphere types in a minute,
but first, let’s look inside the EArth to clarify the layers. The mantle is a 2900 km-thick
rock layer between the crust and core. The composition is high-magnesium silicate. The
uppermost part, the lithospheric mantle, is cooler and more rigid than the deeper mantle.
It lies above a hotter and more-ductile layer of similar composition called the asthenosphere.
As an analogy to how a rock can be either brittle or ductile, consider a taffy bar,
like the Big Hunk. When force is applied it is brittle when cold, and ductile when warm.
Zooming in to a tectonic cross section we see that the lithospheric plates are composed
of crust on top of the outermost rigid part of the mantle. Although the mantle has a different
composition and higher density than the crust, these two layers migrate as a single mechanical
layer called a lithospheric, or tectonic plate. This is where earthquakes occur as brittle
rock fractures and breaks. The hotter and more-ductile asthenospheric rock does not
fracture to produce earthquakes. Continental lithosphere, with continental
crust above lithospheric mantle, typically ranges from 150 to 200 km thick. Continental
crust stands above sea level because it has an average thickness of 40 km and is mostly
more buoyant silica-rich low-density granitic, sedimentary and metamorphic rocks which form
the continents. OCEANIC lithosphere, formed at spreading ridges,
is typically 50–140 km thick. Oceanic crust is only around eight kilometers thick and
is denser than continental crust because it contains less low-density silica, and more
high-density iron and magnesium. Thus, it forms the ocean floor with its top surface
below sea level. Relative motion between plates can be broadly
grouped into three main categories: Transform, Divergent, and Convergent. RETURNING to the
world map view, we show. 1) Transform, or strike-slip, boundaries: where plates move horizontally against each other, 2) Divergent, or constructive, boundaries: where plates move apart from one another, and 3) Places were plates press into one another
are called convergent, or destructive, boundaries. Lithosphere is neither created nor destroyed
along transform boundaries which connect segments of spreading oceanic ridges and other plate
boundaries. Transform boundaries can also cut across continents as the San Andreas Fault Zone
does in California where it connects the East Pacific Rise  to the Cascadia subduction
zone. Shallow earthquakes on long transform boundaries that cut continental crust, can
approach magnitude 8 whereas those on oceanic transform boundaries tend to be smaller.
At divergent boundaries, oceanic crust forms at spreading ridges where plates pull away
from each other. A small volume of the mantle melts to create the crust. The hot, buoyant
upwelling mantle supports the oceanic ridges that forms Earth’s longest mountain systems.
Because temperature increases rapidly with depth at divergent boundaries, there is only
a thin layer of brittle rock to fracture in earthquakes. Most earthquakes occur within
the upper ten kilometers and have magnitudes that are generally less than six.
More than 75% of all earthquakes occur on or near convergent boundaries. Here,
an oceanic plate is forced beneath a continental in a process called subduction. Indeed, the
world’s largest earthquakes occur near the shallow edge of the boundary where magnitude
9’s have been recorded.. At this location stress builds up over 10’s to 100’s of
years until it releases like a spring. and can produce tsunamis. A broad zone of shallow
earthquakes occurs within the overriding plate due to compressive forces near the convergent
boundary. earthquakes can reach depths of 700 km within the subducting plates because
the oceanic plate can remain cold and brittle as it dives into the deeper mantle.
Similar processes occur when an oceanic plate subducts beneath another oceanic plate. Here,
an ocean trench marks the location where the plate is pushed down into the mantle. In this
case, the line of volcanoes that grows on the upper oceanic plate is an island arc.
Not all convergent boundaries involve subduction. When the continental parts of converging plates
come together, neither can subduct. Instead the two continents collide, producing horizontal
deformation and uplift of continental crust to build mountains and plateaus. Frequent
shallow earthquakes in continental collision zones can exceed magnitude 8 and are generally
less than 40 km deep. In addition to these three boundaries, there
are also diffuse boundary zones in which deformation occurs over a wide region. Although less common
than earthquakes along the plate boundaries, earthquakes in the interior part of plates,
called intraplate earthquakes, do occur. Nevertheless, tectonic activity and earthquakes
are chiefly concentrated at, or near plate boundaries where many geological features
including volcanoes, mountains, trenches occur.

41 Replies to “Tectonic Plates—What are the lithospheric plates? (Educational)”

  • HAH where does the other side go?!! one side goes down moving away from something on the other side?? !! How about nonsense

  • I recently made a discovery that if proven correct will change our current understanding of the workings of plate tectonics, do you know anyone that I could contact to discuss and test my findings?

  • 6:10 judging by these plates i dont understand the animation of tectonic activity shown tearing Super continent to shreds towards formation of modern day landscapes … I think that is all wrong … the plates over since they were first formed perhaps have at times elevated land on one side while drowning it on the other but not slingshot India from the corner of south america towards its present day location. I strongly disagree with the explanation scientists offer in text books! Its senseless to make sense of something so complicated to simplified level so to it may become standard procedures of understanding geology! The American plate would always be opposite to Asia, while pacific plate may have been dry land in the past millions upon millions of years ago but its steady downwards flow of movement far explains how the american plate came to be dry land sticking out of water and rubbing against pacific and african plates today.

  • That’s a lot of information platetonics and the
    convecting mantle system process overall. Irene Bethel GOL-106 Summer 2018

  • I am finding uniformitarianism to be quite illogical. Take folded rock layers for instance. We only witness earthquakes at fault lines currently. The folding lies within each continental plate. How did the folding occur? Most folded rock are brittle sedimentary rock. You can’t bend rock very far without breaking . The global catastrophic flood sounds logical having all sedimentary layers soft at the same time to create the folds I see worldwide.

  • Plate: a flat, usually round dish with a slightly raised edge.
    a flat piece of something that is hard and does not bend:.

    Is this what you mean by Tectonic Plate?

  • Hi, thank you for the nice explanatory animation. wonder if yo could do a few videos on how to create this clip with Google earth, or any other packages, specially an animation of all the tectonic plates only without the Occeans and seas. Perhaps only then can I visualize and understand better the net effect forces and then add the oscillating forces of the Oceans. It would be much appreciated. Thanks.
    Further, just out of curiosity, given all the earth quakes to current date, suppose one could predict 9 earth quakes out of 10, what kind of patterns one could pick and investigate further?

  • It sad that people believe this with one side of Earth pushing in an the other out it would great a super mountain. There are plates in the inner core though along the "plate boundaries". Magnetics are the science behind gravity because everything is magnetic everything has an orbit and this is the center of mass between it and what it's orbiting, once it touches it can't escape it's there, unless you use and upward force. And with this you can make an object float in the air. This is true and that would make tectonic plates into a super mountain. Plus Pangea sounds very similar to Paganea. And yes it is a Pagan belief. The mid ocean ridges are the rivers of Eden. Now with this into consideration rethink this article. I'm glad you read this before disliking. Because now you know a truth.

  • It looks like there is a plate that goes through the length of North America based on the earthquake photo at the end. Can you comment on that please?

  • Amy Atkins Gol 105 v1 Fall 2019
    Watching this video for class. I did not know that earthquakes of trans-Oceanic crust pathways are of less magnitude.

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