Figure 6.13P-T paths indicate the trajectory of rocks during metamorphism. (a) Metamorphism of mélange at an ocean-continent convergence zone. (b) Metamorphism at a continent-continent convergence zone. The different P-T paths of rocks formed in these different plate tectonic settings indicate differences in geothermal gradients. Rocks transported to similar depths—and pressures—beneath mountain belts become much hotter than rocks transported to an equivalent depth by subduction.