Dynamics Mechanism of Deep-Earth Water Cycling and Its Research Progress

Mantle transition zone (MTZ) is the transitional region between the upper and lower mantle, the geological processes occurred within its interior have a profound influence on the related geodynamic processes. The subduction zone is one of the strongest crust-mantle interaction regions, and the widespread continental flood basalt (CFB) on the Earth's surface is one of most important objects to study crust-mantle cyclic dynamics. Mantle transition zone has a large amount of water, which is stored within the nominal anhydrous minerals (NAMs). The fluids were caused by the dehydration of residual slab in the subdution process, and these fluids replaced the continental lithosphere, producing the intra-continental basalts with arc-like signature and leading to the misidentification between continental basalt and island-arc basalt. The traditional discrimination diagrams of basalts are not validity distinguishing two types of basalts (CFB and IAB), and it can be further divided by sensitive elements, thus the tectonic discrimination diagrams need to be used. Newly proposed water-filtering model of mantle transition zone links the deep-Earth fluid cycling, large-scale intra-continental basaltic magmatism, and supercontinent cycles into a system. This model reveals that the assemblage of supercontinent could potentially lead to the accumulation of water-bearing oceanic plates in the mantle transition zone and may also change the mode of mantle convection.