Early Archaean subduction and intracrustal processes: experimental evidence from the East Pilbara Terrane, Australia.

The growth and recycling of continental crust has resulted in the modification of Earth's mantle, hydrosphere, atmosphere, and biosphere. Before the formation of the oldest stable continents, the Earth's surface was composed of 25-45 km thick basaltic crust. From 4.3-3.5 billion years ago (Ga), this basaltic crust began to differentiate, generating the first stable silicic continental crust. The tectonic processes responsible for the formation of 4.3-3.5 Ga continental crust remain controversial. Suggested explanations include deep subduction and/or crustal drip/delamination processes and a variety of relatively shallow intracrustal mechanisms. Here, we conduct high-pressure-temperature experiments on a 3.52 Ga early Earth basaltic source rock from the Pilbara Craton, Australia to show that magmas with early continental granitic compositions can form from contemporaneous shallow intracrustal and deep subduction-like tectonic environments. These results suggest that a primitive type of plate tectonics may have operated on the early Earth.