How can pieces of oceanic crust become preserved on continents?

Pieces of oceanic crust are typically consumed at subduction zones, where dense oceanic plates descend into the mantle. However, rare fragments of this crust can be preserved on continents through a process known as obduction.123

During tectonic collisions—such as when an oceanic plate interacts with a continental margin or when island arcs and continental plates collide—small sections of the oceanic crust may break away from the subducting slab. Instead of being pulled into the mantle, these slices are thrust upward and over the overriding plate.34

These preserved fragments are known as ophiolites. They typically consist of a characteristic sequence of rocks, including:3
* Oceanic sediments (such as cherts)
* Pillow-bearing basalts
* Sheeted basic dikes
* Gabbros
* Ultramafic rocks (such as serpentinized harzburgite)4

Because the preservation of oceanic crust is rare, ophiolite complexes serve as vital natural laboratories for geologists to study the composition of the ocean floor and the complex mechanisms of plate tectonics.3