Theory of plate tectonics
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Theory of Plate Tectonics
When the concept of seafloor spreading came along, scientists recognized that it was the mechanism to explain how continents could move around Earth’s surface. Like the scientists before us, we will now merge the ideas of continental drift and seafloor spreading into the theory of plate tectonics
Earth’s Tectonic Plates
Seafloor and continents move around on Earth’s surface, but what is actually moving? What portion of the Earth makes up the “plates” in plate tectonics? This question was also answered because of technology developed during war times – in this case, the Cold War. The plates are made up of the lithosphere.
A map of the world with all earthquakes from 1963 to 1998 plotted. The earthquakes all line up around the plate boundaries.
Figure 1. Earthquakes outline the plates.
During the 1950s and early 1960s, scientists set up seismograph networks to see if enemy nations were testing atomic bombs. These seismographs also recorded all of the earthquakes around the planet. The seismic records could be used to locate an earthquake’s epicenter, the point on Earth’s surface directly above the place where the earthquake occurs.
Earthquake epicenters outline the plates. Mid-ocean ridges, trenches, and large faults mark the edges of the plates, and this is where earthquakes occur (figure 1).
The lithosphere is divided into a dozen major and several minor plates (figure 2). The plates’ edges can be drawn by connecting the dots that mark earthquakes’ epicenters. A single plate can be made of all oceanic lithosphere or all continental lithosphere, but nearly all plates are made of a combination of both.
Map of lithospheric plates
Figure 2. The lithospheric plates and their names. The arrows show whether the plates are moving apart, moving together, or sliding past each other.
Movement of the plates over Earth’s surface is termed plate tectonics. Plates move at a rate of a few centimeters a year, about the same rate fingernails grow.
How Plates Move
Cross-section of the earth. At the center of the earth is the inner core. Surrounding that is the outer core and surrounding that is the mantle, which has convection cells. At the surface is the ocean, upon which is the mid-oceanic ridge
Figure 3. Mantle convection drives plate tectonics. Hot material rises at mid-ocean ridges and sinks at deep sea trenches, which keeps the plates moving along the Earth’s surface.
If seafloor spreading drives the plates, what drives seafloor spreading? Picture two convection cells side-by-side in the mantle, similar to the illustration in figure 3.
Hot mantle from the two adjacent cells rises at the ridge axis, creating new ocean crust.
The top limb of the convection cell moves horizontally away from the ridge crest, as does the new seafloor.
The outer limbs of the convection cells plunge down into the deeper mantle, dragging oceanic crust as well. This takes place at the deep sea trenches.
The material sinks to the core and moves horizontally.
The material heats up and reaches the zone where it rises again.
what are tectonic plates.?
⚫The lithosphere is broken up into plates called as tectonic plates.
⚫On Earth, there are seven or eight major plates and many minor plates.
⚫the shaking or colliding of these tectonic plates causes earthquakes and volcanoes.
=> Tectonic Plates are the plates on which the continents stands.
=> There are 7 major tectonic plates and there are many minor tectonic plates also.
=> The tectonic plates are the large pieces of rock under the earths surface .
=> that are constantly moving and responsible for causing earthquakes and volcanic eruption.
=> Tectonic plates refer to the small bit of layers of earth's crust and topmost layer of mantle.
=> These plates are main cause of mountain formation, volcanoes and tsunamis.
=> A tectonic plate is a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.