When did plate tectonics begin? evidence from the orogenic record

Evidence of modern-style plate tectonics is preserved in the continental rock record as orogens and rifts; these orogens represent regions of mountain building resulting from compression between converging plates. Recognition of orogens in the ancient rock record can help identify when plate tectonics began on Earth. Evidence of Paleoprotero-zoic collisional orogeny is widely accepted. The development, however, of Archean col-lisional orogens is highly controversial, as is the operation of plate tectonics in general. We review the tectonic evolution of three well-studied Archean terranes-the Pilbara craton of Western Australia, the Barberton granite-greenstone terrane of South Africa, and the Superior Province of Canada-in terms of their geological development and evidence for Archean collisional and accretionary plate-tectonic processes in the context of secular evolution of the planet. The Pilbara craton preserves geological, geochemi-cal, and geochronological evidence for continental rifting at 3.2 Ga, development of an oceanic-arc subduction complex at 3.12 Ga, and terrane accretion at 3.07 Ga. The Bar-berton granite-greenstone terrane of the Kaapvaal craton provides thermobarometric evidence for subduction-related high-pressure-low-temperature metamorphism juxtaposed against medium-pressure-high-temperature metamorphism associated with exhumation of high-grade rocks via orogenic collapse, which together are interpreted to represent a paired metamorphic belt. The Superior Province in the Canadian Shield records widespread accretionary and collisional assembly at ca. 2.7 Ga. This evidence argues for "modern-style" plate tectonics on Earth since at least 3.2 Ga.