Thursday , June 24 2021

The water dives deep into the oceanic tectonic plate.



The subducting subdivision of the subterranean tectonic plate into the deep earth serves as a massive conveyor belt that transports water, liquids and volatile compounds to our planet. The water inside the earth is released back into the ocean and atmosphere by volcanoes. These inputs and outputs constitute the deep seawater circulation in the Earth, but it has proved difficult to quantify the total water entering the marine plate. writing nature, Kai outside.One Reported that the Pacific plate submerged in the Mariana Trench contained much more water than previously assumed. This is a major ripple effect on the Earth's water budget.


Water, like the processes on the surface of the earth, is important for the action inside the earth. Among other things, it induces magma generation under the volcano, lubricates the deep faults, and fundamentally changes the power and behavior of the earth mantle. Sea water seeps through fractures and holes into the marine lithosphere and reacts with the crust and minerals to form hydrous minerals (eg serpentine) that store water in the crystal structure.

Water infiltration occurs at several key stages in the life cycle of the oceanic plate. The first is in the middle of the ocean floor when the water circulates through the hot, newly formed ocean floor.2. However, circulation and hydration are mainly confined to the upper surface of the plate in the rapidly expanding ridge (the main 'diet' of the sedimentation zone across the Pacific). The accumulation of sediments subsequently blocks most of the ocean plate at sea, but submarine (underwater mountains) and fractured zones provide a pathway for more water in and out, allowing the circulation to move away from the center of the ocean floorthree. Final infiltration occurs at & # 39; Outside Rise & # 39; of the seabed entry point. Here, it is thought that a renal defect is formed in response to the bending, and enables a hydration process penetrating deeply into the crust and the upper mantle46.

Evidence of water entering the sinking area is evident, but some knowledge gaps have made it difficult to quantify the amount of water flowing along these hatches in individual subsea areas. What is not known is the depth of water through the marine plate. Much of the restraint on estimates comes from controlled seismic data generated by measuring seismic waves generated from artificial sources using a compact array of recording tools. This data provides excellent constraints on crustal and shallow mantle hydration, but with one notable exception7Do not completely inhibit hydration. It is not possible to count the total amount of sediment water because of the unknown total hydration depth.

Another important task is to release all the elements that change the speed at which the seismic waves pass through different parts of the plate. The measurement of such seismic waves is one of the main means of estimating the amount of water in sedimentary oceanic plates. Most speculation is that the reduction in wave speed is the result of turning olivine (a major mineral found in the mantle) into a twisty one. However, in the crust and shallow mantle, water filled cracks can contribute to the rate reduction8. To further complicate matters, the seismic velocities of the upper ocean mantle are anisotropic – they depend on the direction of propagation. This is because, when a new oceanic plate is made at the ridge of the ocean, the olivine crystals are aligned in the direction that the sea floor spreads. Anisotropy can be caused by cracks formed in the external elevation.

Kai outside. The Mariana Trench addresses all of these problems by presenting restrictions on the signage of the Pacific Ocean about 1.5 million years old. The authors analyzed seismic waves of distant earthquakes by the seafloor of the seabed. This allowed us to model the seismic velocity to a much deeper depth than is possible using controlled seismic data (although the resolution is lower).

The researchers have found impressively that the total hydration depth of the lithosphere extends to about 30 km below the seabed (Figure 1). They were also able to investigate the rate of decline in deep areas where the pressure could be high enough to close all the cracks, thus eliminating the impact of these cracks on speed in these areas. Finally, the author was able to account for the effect of anisotropy on wave velocity because he recorded waves traveling all the way across the array.

Figure 1 | Moisture of Pacific tectonic plates in Mariana settlement area. At the Mariana Trench in the Pacific Ocean, Pacific Plates subducts under adjacent Philippine Plates to transport seawater to a deeper Earth. The water exudes through cracks and pores in the plate and reacts with minerals in the crust and mantle to form hydrated earth consisting of minerals that store water in crystal structures. Kai outside.One Earthquake measurements were used to show that water penetrates about 30 km deep from the sea floor. (Approximated in Figure 2d of Ref. 1)

Kai outside. Four times as much water as previously estimated was reported to flow into the Mariana capture area.9. The old and cold sedimentation plates, such as the Mariana trench, are particularly effective at transporting water to the deepest earth because the water minerals contained in the deep plates are more stable than the younger and warmer plates. If the cold plates extrapolate globally to other sinking sites, the author's results indicate that the amount of water entering the Earth greatly exceeds the current estimate10 This is proportional to the amount released by volcanoes, so we need to rethink the global water budget.

Some questions need to be answered in order to better control the estimates of the inputs to the deep-water circulation of the Earth and evaluate the implications of the new outcomes. First, how does the moisture content of the sea surface plate change over the range of depth and scale length along the sea ice extent? Numerous studies have reported changes in synoptic faults and perception and super-mantle hydration in sinking areas, and several competing factors have been proposed to contribute to this change7,11,12. Characterizing this diversity throughout the hydrated part of the plate and understanding its cause is essential to aggregate the water inputs and compare them with the output. It may also be useful to determine whether moisture occurs in concentrated areas of the nearest area, as observed in other perception settings13, Or more evenly distributed. This is because it is possible to control whether mineral binding water is released by dehydration or deeper14.

Finally, since a considerable amount of water is probably stored in the crust and upper mantle (the region most accessible to seawater infiltration), the stringent issue of whether changes in seismic waves reflect the presence of water-filled cracks or hydrological minerals It needs to be handled directly. A comprehensive understanding of the inputs to the interior of the earth will require a multifaceted approach, including multi-scale marine geophysical studies, drilling defects thought to be conduits of water to marine lithosphere, and numerical and laboratory studies. But now the results of Cai and his colleagues have gone a step further in our understanding of the total water resources in the subduction area.

Sign up every day Nature briefing Email newsletter

What is important in science, and why do you pick it up and stay up to date? nature And other worldwide publications.

Sign up


Source link