Controls on the Deep‐Water Cycle Within Three‐Dimensional Mantle Convection Models

Price, Matthew; Davies, John H.; Panton, James

doi:10.1029/2018gc008158

Cited by 9 publications

(13 citation statements)

References 37 publications

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“…However, because deep-mantle plumes must traverse the MTZ, the entrainment and/or melting of hydrated portions of the MTZ may control how water-rich materials are transported to the surface. Price et al (2019) developed a three-dimensional model of water transport in the mantle where the influence of deep mantle melting is included. However, in their model, melt is assumed to be lighter than the coexisting rocks in all situations, and rises to the nearsurface region.…”

Section: Comparison To Other Modelsmentioning

confidence: 99%

Deep mantle melting, global water circulation and its implications for the stability of the ocean mass

Karato

Karki

Park

2020

Prog Earth Planet Sci

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Oceans on Earth are present as a result of dynamic equilibrium between degassing and regassing through the interaction with Earth’s interior. We review mineral physics, geophysical, and geochemical studies related to the global water circulation and conclude that the water content has a peak in the mantle transition zone (MTZ) with a value of 0.1–1 wt% (with large regional variations). When water-rich MTZ materials are transported out of the MTZ, partial melting occurs. Vertical direction of melt migration is determined by the density contrast between the melts and coexisting minerals. Because a density change associated with a phase transformation occurs sharply for a solid but more gradually for a melt, melts formed above the phase transformation depth are generally heavier than solids, whereas melts formed below the transformation depth are lighter than solids. Consequently, hydrous melts formed either above or below the MTZ return to the MTZ, maintaining its high water content. However, the MTZ water content cannot increase without limit. The melt-solid density contrast above the 410 km depends on the temperature. In cooler regions, melting will occur only in the presence of very water-rich materials. Melts produced in these regions have high water content and hence can be buoyant above the 410 km, removing water from the MTZ. Consequently, cooler regions of melting act as a water valve to maintain the water content of the MTZ near its threshold level (~ 0.1–1.0 wt%). Mass-balance considerations explain the observed near-constant sea-level despite large fluctuations over Earth history. Observations suggesting deep-mantle melting are reviewed including the presence of low-velocity anomalies just above and below the MTZ and geochemical evidence for hydrous melts formed in the MTZ. However, the interpretation of long-term sea-level change and the role of deep mantle melting in the global water circulation are non-unique and alternative models are reviewed. Possible future directions of studies on the global water circulation are proposed including geodynamic modeling, mineral physics and observational studies, and studies integrating results from different disciplines.

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Section: Comparison To Other Modelsmentioning

confidence: 99%

Deep mantle melting, global water circulation and its implications for the stability of the ocean mass

Karato

Karki

Park

2020

Prog Earth Planet Sci

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“…Numerous geodynamical studies have investigated the coupled evolution of Earth's interior and surface oceans in hydrous mantle convection, implying that the volume of the surface oceans evolves with time over billion‐year timescales (e.g., Crowley et al., 2011; a 2008; Korenaga et al., 2017; Nakagawa & Iwamori, 2019; Price et al., 2019; Sandu et al., 2011). However, most of the existing geodynamical models did not take into account the mineral physics constraints on mantle water storage; some assumed that the solid mantle is a water reservoir with infinite storage capacity.…”

Section: Introductionmentioning

confidence: 99%

Constraining the Volume of Earth's Early Oceans With a Temperature‐Dependent Mantle Water Storage Capacity Model

et al. 2021

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Water was delivered to the Earth during accretion or soon afterward (Morbidelli et al., 2000). This was followed by vigorous outgassing of possibly oxidized volcanogenic gases, including H 2 O (Hirschmann, 2012), from the early Earth's mantle, which may have led to the formation of primordial oceans (Elkins-Tanton, 2011). Sometime after the onset of plate tectonics, mantle rehydration by subduction (Iwamori, 2007; Rüpke et al., 2004; van Keken et al., 2011) began to change the relative water contents of the surface and internal reservoirs. Extensively preserved eustatic sea-level records indicate that the continental freeboard has been approximately constant throughout the Phanerozoic (541 Ma to the present) (Miller et al., 2005). However, the subaqueous and subaerial proportions of the Earth's surface may have been quite different before the Phanerozoic, especially in the early Archean, approximately from the Eoarchean to the Paleoarchean (4-3.2 Ga). Though they are sparse, isotopic records from the early Archean may be used to indirectly constrain the size of the early

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“…F d = 1 in all of these models, assuming the most efficient transport to the surface. Whilst lower values are unexpected (Rüpke et al, 2013), values of F d ranging from 0 to 1 are tested (Fig. A4) show that the amplitude of net degassing is most affected.…”

Section: Periods Of Net Degassingmentioning

confidence: 93%

“…Sleep et al, 2014) such as heat pipe (Moore and Webb, 2013), 'squishy lid' tectonics (Lourenço et al, 2018) and incorporation into complex, 2D and 3D models. Hints of net degassing have been seen in 2D (Nakagawa and Nakakuki, 2019) and 3D (Price et al, 2019) models, but not yet discussed. Nakagawa and Nakakuki (2019) show transitions on 0.1 Gyrs scale whereas Price et al (2019) show cases where net degassing occurs for 0.5 Gyrs.…”

Section: Implications For Earthmentioning

confidence: 99%

“…Hints of net degassing have been seen in 2D (Nakagawa and Nakakuki, 2019) and 3D (Price et al, 2019) models, but not yet discussed. Nakagawa and Nakakuki (2019) show transitions on 0.1 Gyrs scale whereas Price et al (2019) show cases where net degassing occurs for 0.5 Gyrs. Variations are on the scale of 130 ppm which would correspond to changes in over 1 km of sea level.…”

Section: Implications For Earthmentioning

confidence: 99%

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The coupled effects of mantle mixing and a water-dependent viscosity on the surface ocean

Chotalia

Cagney

Lithgow‐Bertelloni

et al. 2020

Earth and Planetary Science Letters

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Water content plays a vital role in determining mantle rheology and thus mantle convection and plate tectonics. Most parameterised convection models predict that Earth initially underwent a period of rapid degassing and heating, followed by a slow and sustained period of regassing and cooling. However, these models assume water is instantaneously mixed and homogeneously distributed into the mantle. This is a limitation because the mixing time for water entering and leaving the mantle is a function of the Rayleigh number which varies dramatically with water content, temperature, and through time. Here we present an adapted parametrised model (Crowley et al., 2011) to include the coupled effects of the time scale of mixing with a water-dependent viscosity. We consider two mixing types: first, where the mixing time is constant throughout the model and second, where mixing time varies as a response to an evolving Rayleigh number. We find that, facilitated by the effects of water content in the melt region at mid-ocean ridges, a constant mixing time can induce long periods of degassing. The inclusion of a variable mixing time dependent on the Rayleigh number acts to limit the period of degassing and also results in more water being stored in the mantle and less at the surface than in both the constant and instantaneous mixing cases. Mixing time cannot be more than ∼2 billion years as large mixing times trap water in the mantle, leaving a dry surface. Even small changes in the surface ocean induced by mixing times on the order of 0.1 Gyrs can cause changes in the global-mean sea level on the order of 10's of metres. These changes in sea level could easily uncover topographic highs in the bathymetry, potentially aiding sub-aerial erosion a process thought to be important in early Earth evolution. Even in this relatively simple model, the inclusion of a mixing time between water entering and leaving the mantle creates a more dynamic water cycle.

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Controls on the Deep‐Water Cycle Within Three‐Dimensional Mantle Convection Models

Cited by 9 publications

References 37 publications

Deep mantle melting, global water circulation and its implications for the stability of the ocean mass

Deep mantle melting, global water circulation and its implications for the stability of the ocean mass

Constraining the Volume of Earth's Early Oceans With a Temperature‐Dependent Mantle Water Storage Capacity Model

The coupled effects of mantle mixing and a water-dependent viscosity on the surface ocean

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