Water-Induced Mantle Overturns Leading to the Origins of Archean Continents and Subcontinental Lithospheric Mantle

The origins of Archean continents and subcontinental lithospheric mantle (SCLM) were important events in the early Earth. The mechanisms for the origins of Archean continents and the SCLM remain unclear. This study suggests that these events were controlled by the evolution of the hydrous magma ocean (MO). With solidification, the basal MO eventually became gravitationally unstable because of the enrichment of water. The triggered massive mantle overturns resulted in the major pulses of the crust and thick SCLM generations. The model avoids a fatal drawback of the oceanic plateau model for the origin of continents: the source of H2O needed for the formation of tonalite-trondhjemite-granodiorite (TTG). The model can also account for why the TTG and thick SCLM basically occurred in the Archean. Among the inner solar system planets, the Earth is the only planet that has continental crust, plate tectonics, and life. The formation of Archean continents, which should play a crucial role in the initiation of plate tectonics and the evolution of life, remains hotly debated. In this study, we show that water in the basal magma ocean plays a fundamental role in the formation of Archean continents. With progressive crystallization, the basal magma ocean becomes increasingly enriched in water because the major lower-mantle minerals have limited water storage capacity. The basal magma ocean eventually becomes gravitationally unstable because of the enrichment of water and generates mantle overturns. The mantle overturns transported a large amount of water upward to the shallow part of the Earth and controlled the formation of the continental crust and can account for many observations including the source of H2O needed for generation of the continental crust and the major pulse of crustal growth around the end of the Archean. Water in the basal magma ocean plays a fundamental role in the formation of Archean continents and subcontinental lithospheric mantleThe basal magma ocean eventually became gravitationally unstable and generated the mantle overturns because of the enrichment of waterThe water-induced mantle overturns resulted in the major pulses of the thick subcontinental lithospheric mantle and continental crust generations in the Neoarchean