Felsic magmatism during Precambrian flat subduction

The modern Earth's crust is predominantly preserved in continents, marking a significant shift from early Earth when oceanic crust was far more dominant. The growth of continental crust, composed largely of felsic rocks, began ∼4 billion years ago in the Archean eon. The origins of these felsic rocks and thus the mechanism behind continental crust formation remains debatable, with contrasting tectonic regimes proposed for the Archean. Our new numerical modeling of intraoceanic plate convergence at elevated mantle potential temperatures (150‒200 °C higher than present day) corresponding to the early Earth shows a shallow-dipping (flat) regime of subduction and voluminous felsic magmatism (plutonic and related volcanic) forming a thin felsic crust on top of the overriding oceanic plate. This is in strong contrast to the modern deep and steep subduction regime, which results in notably less generation of both basaltic and felsic magmas. Further modeling shows that during subsequent flat subduction of oceanic crust containing thin felsic domains, these buoyant crustal segments detach from the shallow slab portions. They rise as diapirs through the serpentinised mantle wedge, thereby forming a thick nucleus of continental crust within the oceanic crust of the upper plate. The modeled migration of felsic melts and rocks through the mantle wedge is in agreement with the presence of Precambrian sanukitoids and to some extent by Mg, Ni, and Cr enrichment in rocks from tonalite-trondhjemite-granodiorite (TTG) suites. Therefore, we conclude that shallow Precambrian subduction likely contributed notably to the formation and recycling of continental crust in Earth's early history.