Two principal models have been proposed to explain the origin of Archean continents: a subduction-dominated island-arc model and a mantle plume–dominated oceanic plateau model. The oceanic plateau model better accounts for geological and geochemical features preserved in Archean continental rocks. However, it faces a critical challenge in explaining the source of water, which is essential for the formation of Archean continents. Concurrently, paleomagnetic studies reveal that paleointensities reached exceptionally high levels during the Archean continental growth. Traditional models for the early geodynamo, such as a silicate dynamo or the exsolution of light elements from the core, have difficulty explaining this phenomenon.
According to current theories, the Moon-forming giant impact is thought to produce a whole-mantle magma ocean. High-pressure studies indicate that the magma ocean separated into an outer magma ocean and a basal magma ocean during crystallization. A research group led by Professor Zhongqing Wu from the University of Science and Technology of China showed that, the basal magma ocean became gravitationally unstable in the Archean because incompatible water accumulated in it, which triggered mantle overturn. The hot, water-rich upwelling magma in this event not only supplied the essential materials and conditions required for the formation of Archean continents, but also offered a unified explanation for many independent observations at that time, such as global lithological transitions and the widespread large igneous provinces (Wu et al., 2023).
In their recent study, the researchers incorporated mantle overturn into models of Earth’s thermal evolution and geodynamo. The results indicate that the upwelling of hot basal magma ocean substantially accelerated the cooling of the core, thereby strengthening the geodynamo, and providing a plausible explanation for the high paleointensities in the Archean. Both the generation of Archean continents and the strong geodynamo result from the mantle overturn, and are therefore temporally correlated. These findings present a coherent picture of how mantle overturn shaped the evolution of Earth from the core to the surface.
Wu, Z., Song, J., Zhao, G., & Pan, Z. (2023). Water-induced mantle overturns leading to the origins of Archean continents and subcontinental lithospheric mantle. Geophysical Research Letters, 50, e2023GL105178. https://doi.org/10.1029/2023GL105178
National Science Review
Computational simulation/modeling