Deep formation of Earth's earliest continental crust consistent with subduction

About four billion years ago, Earth's outer layer is thought to have been composed mostly of a 25- to 50-km-thick basaltic crust that differentiated to form the oldest stable continental crust. However, the tectonic processes responsible for the formation of this continental material remain controversial. Suggested explanations include convergent plate boundary processes akin to subduction operating today and a variety of relatively shallow (< 50 km) non-plate-tectonic intracrustal mechanisms. Here we perform high-pressuretemperature melting experiments on an oceanic plateau analogue for the early basaltic crust and show that magmas with the composition of the early continental crust cannot form at pressures < 1.4 GPa (> 50 km depth). This suggests that Eoarchaean continental magmas are formed in deep > 50 km) subduction-like environments. Our results support previous Eoarchaean field evidence and analyses of igneous rocks that date to 4.0-3.6 billion years ago, which are consistent with subduction-like processes and suggest a primitive type of plate tectonics operated as long as 4 billion years ago on early Earth.