Difference Between Oceanic Crust And Continental Crust

What Is Oceanic Crust?

Oceanic crust is the outermost solid layer of the lithospheric tectonic plates under the oceans that covers much of the Earth’s surface. It has a distinctive basaltic composition characterized by rocks that have relatively low concentrations of potassium and other highly incompatible trace elements (those typically excluded from minerals that comprise the mantle). 

The oceanic crust lies atop Earth’s mantle, as does the continental crust. Mantle rock is composed mostly of peridotite, which consists primarily of the mineral olivine with small amounts of pyroxene and amphibole.

Oceanic crust is formed by divergent plate boundaries. These zones, located along mid-ocean ridges, represent areas where upwelling magma creates new oceanic crust. As lava flows from these volcanic ridges, it quickly cools, forming extrusive igneous rock.

Oceanic crust is about 6 km (4 miles) thick. It consists of three layers:

• A relatively thin topmost layer which is about 500 metres (1,650 feet) thick, and includes lavas made of basalt (that is, rock material consisting largely of plagioclase [feldspar] and pyroxene).
• A thicker layer of more coarsely crystalline, intrusive basaltic dikes that feed the volcanic layer; and
• A thick lowermost layer of intrusive coarse-grained gabbros that mostly represent minerals that have settled out of slowly cooled melt bodies and lenses in a crystal mush zone below ridge crests.

Oceanic crust differs from continental crust in several ways: it is thinner, denser, younger, and of different chemical composition. Like continental crust, however, oceanic crust is destroyed in subduction zones.

The age of the oceanic crust does not go back farther than about 200 million years. Such crust is being formed today at oceanic spreading centres. Many ophiolites are much older than the oldest oceanic crust, demonstrating continuity of the formation processes over hundreds of millions of years. 

What You Need To Know About Oceanic Crust

• The oceanic crust is the component of the earth’s crust that makes up the ocean basins.
• The oceanic crust is mainly made out of dark basalt rocks that are rich in minerals and substances like silicon, calcium and magnesium.
• Oceanic crust is found under oceans and it is about 4 miles thick in most places.
• Oceanic crust has a higher density than the continental crust. Oceanic crust has a density of about 3.0 g/cm³.
• The oceanic crust is younger than the continental crust. The oldest oceanic rocks are less than 200 million years old.
• Oceanic crust is formed by divergent plate boundaries. These zones, located along mid-ocean ridges, represent areas where upwelling magma creates new oceanic crust. As lava flows from these volcanic ridges, it quickly cools, forming extrusive igneous rock.

What Is Continental Crust?

Continental crust is the outermost layer of the Earth’s lithosphere that makes up the Earth’s continents and continental shelves and is formed near subduction zones at plate boundaries between continental and oceanic tectonic plates. The continental crust forms nearly 90% of all Earth’s land surface.

Continental crust is formed primary by convergent plate boundaries. These zones represent areas where oceanic plates collide with and plunge underneath continental plates-a process referred to as subduction. As oceanic plates subduct, they melt to form magma. This magma cools over millions of years, producing intrusive igneous rock and new continental crust.

Continental crust is broadly granitic in composition and, with a density of about 2.7 grams per cubic cm, is somewhat lighter than oceanic crust, which is basaltic (i.e., richer in iron and magnesium than granite) in composition and has a density of about 2.9 to 3 grams per cubic cm. Continental crust is typically 40 km (25 miles) thick, while oceanic crust is much thinner, averaging about 6 km (4 miles) in thickness.

The effect of the different densities of lithospheric rock can be seen in the different average elevations of continental and oceanic crust. The less-dense continental crust has greater buoyancy, causing it to float much higher in the mantle. Its average elevation above sea level is 840 metres (2,750 feet), while the average depth of oceanic crust is 3,790 metres (12,400 feet). This density difference creates two principal levels of Earth’s surface.

What You Need To Know About Continental Crust

• The continental crust is that part of the crust that makes up the earth’s surface. In fact, about 45% of the surface of earth is made up of this layer. The continental crust helps continents of the world to stay in one place.
• The continental crust is made up of light-colored granite rocks full of substances like oxygen, aluminum, sodium, potassium and silicon.
• Continental crust varies between six and 47 miles in thickness depending on where it is found.
• Continental crust has a lower density when compared to the oceanic crust. The continental crust has a density of about 2.6 g/cm³.
• The continental crust is older than the oceanic crust. Much of the continental crust exceeds 1 billion years in age, and its oldest rocks may be as old as 4 billion years.
• Continental crust is formed primary by convergent plate boundaries. These zones represent areas where oceanic plates collide with and plunge underneath continental plates-a process referred to as subduction. As oceanic plates subduct, they melt to form magma. This magma cools over millions of years, producing intrusive igneous rock and new continental crust.

Also Read: Difference Between Ocean And Sea

Difference Between Oceanic Crust And Continental Crust In Tabular Form