Notes

The heat and pressure needed for many changes in the rock cycle are only possible under extreme conditions. The movement of tectonic plates helps provide these conditions. Tectonic plates, which make up the Earth’s crust and upper mantle, are constantly in motion. These movements can create heat and pressure, which can then form metamorphic rock.


The Earth’s crust and upper mantle are broken into tectonic plates. The movement of these plates plays several roles in the rock cycle.



The movement of the plates also contributes to the formation of igneous rock. Plate movement helps form magma, which cools to form igneous rock. One specific way that igneous rock may form is when plates move apart. As plates separate, they create a rift zone with low pressure. The low pressure in the rift zone allows rock to rise up and partially melt to form magma, which can then cool to form igneous rock.


As tectonic plates pulled apart, they formed this rift zone in Hawaii. Igneous rock frequently forms at rift zones.



Plate tectonics also play a role in the formation of sedimentary rock, through the processes of uplift and subsidence. During the process of uplift, parts of the Earth’s crust rise, such as when plates collide to form mountains. These raised areas will eventually weather, and erosion will carry the resulting sediment away. During the process of subsidence, parts of the Earth’s crust sink, forming basins. Sediment may be deposited in basins, where it will compact into sedimentary rock. Through all of these changes, the amount of material stays the same. Rock is constantly being created and destroyed.