What Are The Types Of Tectonic Plates?
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Tectonic plates are divided into two main types based on composition. Continental plates are thicker (20-30 miles), less dense, and made mainly of granitic rocks. Oceanic plates are thinner (3-6 miles), denser, and made mainly of basaltic rocks. Most actual plates contain both continental and oceanic crust portions.
Tectonic plates aren't all the same. They're divided into two main types based on the crust they carry: continental and oceanic. The distinction matters because the two types behave differently at plate boundaries, with denser oceanic plates typically sinking beneath continental plates during subduction. Understanding the two types reveals key principles of how plate interactions shape Earth's surface.
What is a continental plate?
A continental plate is a tectonic plate that consists mainly of continental crust, the type of rock that forms the continents. Continental crust is thicker (20-30 miles, or 30-50 km), less dense (averaging about 2.7 g/cm³), and composed mostly of granitic rocks rich in silicon and aluminum. The thickness and low density let continental crust float higher on the asthenosphere, forming the elevated continents we see. Most continental crust is very old, with some rocks dating back 4 billion years. Continental crust is buoyant enough that it generally avoids being subducted into the mantle.
What is an oceanic plate?
An oceanic plate is a tectonic plate that consists mainly of oceanic crust, the type of rock that forms the ocean floor. Oceanic crust is thinner (3-6 miles, or 5-10 km), denser (averaging about 3.0 g/cm³), and composed mostly of basaltic rocks rich in iron and magnesium. The greater density makes oceanic plates float lower on the asthenosphere, forming the ocean basins. Oceanic crust is relatively young geologically, with the oldest being about 200 million years old; everything older has been subducted. New oceanic crust continuously forms at mid-ocean ridges.
How do continental and oceanic plates differ?
Continental and oceanic plates differ in several important ways. Continental crust is granitic (lighter color, less dense, more silica) while oceanic crust is basaltic (darker, denser, less silica). Continental plates can be much older (billions of years) than oceanic plates (maximum about 200 million years). Continental crust is much thicker than oceanic. Continental crust floats higher, forming continents above sea level; oceanic crust forms basins below sea level. The chemical and physical differences explain why continents persist while ocean floors continuously recycle through the mantle.
What happens where the two types meet?
When continental and oceanic plates meet at a boundary, the denser oceanic plate subducts (sinks) beneath the lighter continental plate. This process creates several distinctive features. Deep ocean trenches form at the subduction zone (the Peru-Chile Trench off South America is an example). Volcanic mountain ranges develop on the continental side as the subducting plate melts in the hot mantle (the Andes formed this way). Earthquakes occur along the subduction zone, including some of the most powerful ever recorded. The interaction is dramatic compared to two oceanic or two continental plates colliding.
Tectonic plates are divided into two main types based on the crust they carry. Continental plates are thicker, less dense, and mostly granitic, floating higher to form continents. Oceanic plates are thinner, denser, and mostly basaltic, forming ocean basins. When the two meet, the denser oceanic plate subducts beneath the continental plate, creating deep trenches, volcanic mountains, and major earthquakes.
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