Earth is a giant fluid factory, according to Santosh and coworkers, researchers from Japan. The authors propose a new model for the nature and distribution of fluids from the core to Earth’s based on modern concepts of plate tectonics and argue that fluids within Earth play a critical role in constraining both the interior Earth dynamics and the evolution of the surface and near-surface environment.
They are of the opinion that the global material circulation in our planet is controlled by a combination of processes that operate on the surface of Earth (plate tectonics), in the intermediate depths (plume tectonics), and at the core-mantle boundary region (anti-plate tectonics). They envisage that hot, rising plumes act as giant pipes connecting the deeper portions of Earth with the surface.
Santosh et al. propose that free fluid circulation within Earth occurs only within restricted zones, such as along regions were tectonic plates are subducted. The water subducted along the plate boundaries reaches up to the 410-660 km boundary termed as the mantle transition zone. Water stored in dense hydrous silicates in this region constitutes a huge water tank with a capacity of nearly five times the volume of the water in modern oceans.
The authors also propose that for the major part of Earth's history, the fluid transport was mostly one way -- from the outer core to the surface. The return flow of water probably started 750 million years ago and the penetration of water to deep levels through plate subduction provided adequate lubrication to transport some of the deeply subducted rocks back to the surface in the younger Earth. Such rocks returned from depth are identified from their ultrahigh-pressure mineral assemblages.
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