Above the yield strength, or elastic limit , a rock will begin to flow in response to high pressure. Plastic deformation results in permanent shape change without rock failure due to rupture. At these constructive sites the plates move extensionally apart from one another. Examples include mid-ocean ridges and continental rift regions. Convergent plate boundaries occur where crust of one plate collides with crust of another plate.
Compression deforms both lithospheric components at such destructive margins.
Large mountain ranges form at sites of continent-continent collision. Transform plate boundaries occur where crust of one plate moves adjacent to crust of another plate. At shear boundaries, forces neither create nor destroy large volumes of crust. Transfer motion essentially conserves crust as plates move laterally past one another. Three tectonic plates meet at triple junctions .