[S-IT15] Mass and energy transport properties and processes in the crust and the mantle

[SIT15-P05] Water-induced mantle overturns leading to the origins of Archean continents and subcontinental lithospheric mantle

*Zhongiqng Wu^1,2,3、Jiang Song¹、Guochun Zhao^4,5、Zhongxu Pan¹ (1.Deep Space Exploration Laboratory / School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, China.、2.CAS Center for Excellence in Comparative Planetology, University of Science and Technology of China, Anhui, China.、3.National Geophysical Observatory at Mengcheng, University of Science and Technology of China, Anhui, China.、4.Department of Earth Sciences, The University of Hong Kong, Hong Kong, Hong Kong、5.Department of Geology, State Key Laboratory of Continental Dynamics, Northwest University, Xi'an, China)

キーワード：mantle overturn, deep water cycle, origin of Archean craton

The originations of the Archean continents and sub continental lithospheric mantle (SCLM) are most important events in the early Earth and crucial for understanding how the early Earth worked and the initiation of modern-style plate tectonics. This study suggests that these events were controlled by a special deep-water cycle in the early Earth (Fig. 1). The early Earth may have experienced a deep water cycle totally different from the current. The whole-mantle magma ocean created by the moon-forming giant impact evolved into an outer magma ocean and a basal magma ocean. The basal magma ocean at the beginning must have contained a certain amount of water since extensive studies suggest substantial accretion of water-rich bodies during the core formation. With the solidification going, water in the basal magma ocean moved toward the core-mantle boundary and the basal magma ocean eventually became gravity unstable because of the enrichment of water. The gravity instability triggered the massive mantle overturns and transported a huge amount of water upward to the shallow part of the Earth.

The massive overturn events resulted in the major pulses of the thick SCLM and continental crust generations in the Neoarchean. The mantle overturns probably got rid of the whole basal magma ocean and the mechanism which generated the Archean-type SCLM and continents likely no more worked after the overturns. Thus, the deep-water-cycle model can account for why Archean-type SCLM and continents basically occurred in the Archean. The deep-water-cycle model can avoid a fatal drawback on the popular oceanic plateau model for the origin of continents, which cannot well explain the source of H₂O needed for the generation of the Archean continental crust. The deep-water-cycle model also shows why only the Earth among inner solar system planets was covered with the continental crust since Mars and Mercury are too small to form the basal magma ocean, while Venus may not experience a whole-mantle magma ocean.

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