What causes the pressure that allows diamons to form in the mantle?

Diamonds form in the Earth's mantle under conditions of high pressure and temperature, typically at depths of 140 to 190 kilometers (87 to 118 miles). The immense pressure, often exceeding 725,000 pounds per square inch, is caused by the weight of the overlying rock layers. Additionally, tectonic processes, such as subduction, can further enhance the pressure and facilitate the formation of diamonds from carbon sources, including organic material and carbonate minerals.