Continental Crust Objectives: To be able to define what continental crust is; To be able to explain how continental crust forms; To be able to describe the composition of continental crust; and To be able to draw a diagram of the structure of continental crust.

Definition The continental crust is the layer of granitic and sedimentary rock which forms the continents and the areas of shallow seabed close to their shores, known as continental shelves.

Formation Accretion - process by which material is added to a tectonic plate laterally - material may be sediment, volcanic arcs, seamounts or other igneous features 2. Volcanism - process by which an opening in the earth's crust occurs, through which molten lava, ash, and gases are ejected - material is added vertically to the continent 3. Erosion & Deposition - rock material is removed from the interior of a continent, then deposited along the margins - materially is added laterally to the continent 4. Underplating - addition of magma from the mantle to the underside or bottom of a plate as it accumulates and solidifies - materially is added vertically to the continent

Composition It is less dense than the material of the mantle and thus "floats" on top of it. The relative low density keeps the continental crust from being re-cycled or subducted back into the mantle. For this reason the oldest rocks on Earth are within the continents rather than in repeatedly re-cycled oceanic crust.

Structure It is also less dense than oceanic crust and considerably thicker averaging 20 to 80 km versus the average oceanic thickness of around 5-10 km. Continental crust is thickest beneath mountain ranges with a deep root. About 40% of the Earth's surface is underlain by continental crust.

Continental Crust Model of the Eastern United States

Continental Crust Model of the Western United States

Subduction and Accretion due to Compression

This map shows elongate belts of rocks with similar types and ages that make up the Earth’s continental crust.

Conclusion Continental Crust is a layer of granitic and sedimentary rock at the Earth’s surface It forms from accretion, volcanism, erosion and deposition, and underplating It is composed of minerals richer in Silica and is less dense than Oceanic Crust It is 20-80 km thick and underlies approximately 40% of the Earth’s surface It is important to study in order to understand where resources form as well as to understand natural hazards associated with it