Extended Data Fig. 2: Comparison between T/P values for the Orocopia–Pelona–Rand schist and for the entire dataset used in this study.

a, All data are divided into low-, intermediate- and high-T/P after ref. ⁴. b, Moving averages (300-Myr window) and one-standard-deviation envelopes of the data shown in a. The OPRS is thought to have formed in response to a transition from steeper, colder subduction (‘Franciscan-type’) to shallower (more gently dipping), hotter subduction related to the incoming of an oceanic plateau (thicker, more buoyant oceanic lithosphere)²⁶. Many Mesoproterozoic and Palaeoproterozoic orogenic belts preserve bimodal distributions of metamorphism, with the lower-T/P rocks (‘intermediate-T/P’ in this figure) being characterized by average T/P similar to that of the OPRS (about 500–650 °C GPa⁻¹)²⁶, including the Grenville, Sveconorwegian, Trans-North China, Trans-Hudson, Eburnean, Ubendian–Usagaran and Belomorian belts.