What two types of crust are the tectonic plates made from?

Answer 1

Short Answer:

The Earth has two types of crust, continental crust and oceanic crust. Basaltic rocks are the main component of oceanic crust. Continental crust consists mainly of lower density granitic rocks.

The Better Answer:

Tectonic plates and the Earth's crust are not the same thing.

Tectonic plates are made of the Earth's crust, plus the upper layers of the Earth's mantle. Together the crust and the more solid upper mantle form the lithosphere.

The crust itself is relatively thin, varying from a few kilometers thick to nearly a hundred kilometers. With the material of the mantle, the tectonic plates are 50 to 200 kilometers thick. Some plates are entirely continental and some are entirely oceanic and some are combined.

Continental crust and oceanic crust are different in make up and properties.

The continental crust has a density of about 2.7 g/cm3 and is mostly granitic, made of silicate materials with more aluminum and less iron and magnesium. Continental crust is generally thicker, in the range of 25 to 70 kilometers.

Oceanic crust is more dense (density of about 2.9 g/cm3) and the average oceanic thickness is in the range of 7-10 kilometers. Oceanic crust is primarily basalt, composed of silicate material which is rich in iron and magnesium.

Though only 40% of the Earth's surface is continental crust, there is more of it because it is thicker. Continental crust is about 70% of the volume of Earth's crust.

Both types of crusts are less dense than the material of the Earth's mantle (density of about 3.3 g/cm3), so the "float" on the mantle.