Lava or magma in contact with other rock causes Contact Metamorphism . Hornfels is a common contact metamorphic rock. Diabase weathers tan. Host rocks are red siltstones. Pressure Burial Pressure .
Pressure increases with depth due to the weight of the overlying rocks.
A cubic foot of granite weighs 167.9 pounds. Increase of pressure and temperature with depth causes Regional Metamorphism . Regional metamorphism occurs at depths of 5 - 40 km. Tectonic pressures associated with convergent plate boundaries and continental collision also cause Regional Metamorphism . Pressure along fault zones causes Dynamic Metamorphism , the crushing and ductile flow of rock.