scholarly journals The fate of water within Earth and super-Earths and implications for plate tectonics

2017 ◽  
Vol 375 (2094) ◽  
pp. 20150394 ◽  
Author(s):  
Sonia M. Tikoo ◽  
Linda T. Elkins-Tanton
Keyword(s):  
Upper Mantle ◽  
Plate Tectonics ◽  
Extrasolar Planets ◽  
Internal Heat ◽  
Magma Ocean ◽  
Nominally Anhydrous Minerals ◽  
The Earth ◽  
Giant Impacts ◽  
Crystallographic Defects

The Earth is likely to have acquired most of its water during accretion. Internal heat of planetesimals by short-lived radioisotopes would have caused some water loss, but impacts into planetesimals were insufficiently energetic to produce further drying. Water is thought to be critical for the development of plate tectonics, because it lowers viscosities in the asthenosphere, enabling subduction. The following issue persists: if water is necessary for plate tectonics, but subduction itself hydrates the upper mantle, how is the upper mantle initially hydrated? The giant impacts of late accretion created magma lakes and oceans, which degassed during solidification to produce a heavy atmosphere. However, some water would have remained in the mantle, trapped within crystallographic defects in nominally anhydrous minerals. In this paper, we present models demonstrating that processes associated with magma ocean solidification and overturn may segregate sufficient quantities of water within the upper mantle to induce partial melting and produce a damp asthenosphere, thereby facilitating plate tectonics and, in turn, the habitability of Earth-like extrasolar planets. This article is part of the themed issue ‘The origin, history and role of water in the evolution of the inner Solar System’.

On the fate of water in the formation of rocky planets

2021 ◽  
Author(s):  
Lindy Elkins-Tanton ◽  
Jenny Suckale ◽  
Sonia Tikoo
Keyword(s):  
Water Content ◽  
Upper Mantle ◽  
Lower Mantle ◽  
Plate Tectonics ◽  
Solidus Temperature ◽  
Magma Ocean ◽  
Excess Water ◽  
Low Degree ◽  
Giant Impacts ◽  
Rocky Planets

<p>Rocky planets go through at least one and likely multiple magma ocean stages, produced by the giant impacts of accretion. Planetary data and models show that giant impacts do not dehydrate either the mantle or the atmosphere of their target planets. The magma ocean liquid consists of melted target material and melted impactor, and so will be dominated by silicate melt, and also contain dissolved volatiles including water, carbon, and sulfur compounds.</p><p>As the magma ocean cools and solidifies, water and other volatiles will be incorporated into the nominally anhydrous mantle phases up to their saturation limits, and will otherwise be enriched in the remaining, evolving magma ocean liquids. The water content of the resulting cumulate mantle is therefore the sum of the traces in the mineral grains, and any water in trapped interstitial liquids. That trapped liquid fraction may in fact be by far the largest contributor to the cumulate water budget.</p><p>The water and other dissolved volatiles in the evolving liquids may quickly reach the saturation limit of magmas near the surface, where pressure is low, but degassing the magma ocean is likely more difficult than has been assumed in some of our models. To degas into the atmosphere, the gases must exsolve from the liquid and form bubbles, and those bubbles must be able to rise quickly enough to avoid being dragged down by convection and re-dissolved at higher pressures. If bubbles are buoyant enough (that is, large enough) to decouple from flow and rise, then they are also dynamically unstable and liable to be torn into smaller bubbles and re-entrained. This conundrum led to the hypothesis that volatiles do not significantly degas until a high level of supersaturation is reached, and the bubbles form a buoyant layer and rise in diapirs in a continuum dynamics sense. This late degassing would have the twin effects of increasing the water content of the cumulates, and of speeding up cooling and solidification of the planet.</p><p>Once the mantle is solidified, the timeclock until the start of plate tectonics begins. Modern plate tectonics is thought to rely on water to lower the viscosity of the asthenosphere, but plate tectonics is also thought to be the process by which water is brought into the mantle. Magma ocean solidification, however, offers two relevant processes. First, following solidification the cumulate mantle is gravitationally unstable and overturns to stability, carrying water-bearing minerals from the upper mantle through the transition zone and into the lower mantle. Upon converting to lower-mantle phases, these minerals will release their excess water, since lower mantle phases have lower saturation limits, thus fluxing the upper mantle with water. Second, the mantle will be near its solidus temperature still, and thus its viscosity will be naturally low. When fluxed with excess water, the upper mantle would be expected to form a low degree melt, which if voluminous enough with rise to help form the earliest crust, and if of very low degree, will further reduce the viscosity of the asthenosphere.</p>

3. Minerals and the interior of the Earth

2014 ◽  
Author(s):  
David Vaughan
Keyword(s):  
Upper Mantle ◽  
Lower Mantle ◽  
Plate Tectonics ◽  
Inner Core ◽  
Indirect Evidence ◽  
Outer Core ◽  
The Earth ◽  
Granite Formation ◽  
Temperature And Pressure

‘Minerals and the interior of the Earth’ looks at the role of minerals in plate tectonics during the processes of crystallization and melting. The size and range of minerals formed are dependent on the temperature and pressure of the magma during its movement through the crust. The evolution of the continental crust also involves granite formation and processes of metamorphism. Our understanding of the interior of the Earth is based on indirect evidence, mainly the study of earthquake waves. The Earth consists of concentric shells: a solid inner core; liquid outer core; a solid mantle divided into a lower mantle, a transition zone, and an upper mantle; and then the outer rigid lithosphere.

scholarly journals Bifurcation in the history of Uranus and Neptune: the role of giant impacts

2019 ◽  
Vol 492 (4) ◽  
pp. 5336-5353 ◽  
Author(s):  
Christian Reinhardt ◽  
Alice Chau ◽  
Joachim Stadel ◽  
Ravit Helled
Keyword(s):  
High Resolution ◽  
Heat Source ◽  
Gravity Data ◽  
Internal Heat ◽  
Internal Heat Source ◽  
Oblique Impact ◽  
Deep Interior ◽  
History Of ◽  
Giant Impacts

ABSTRACT Despite many similarities, there are significant observed differences between Uranus and Neptune: While Uranus is tilted and has a regular set of satellites, suggesting their accretion from a disc, Neptune’s moons are irregular and are captured objects. In addition, Neptune seems to have an internal heat source, while Uranus is in equilibrium with solar insulation. Finally, structure models based on gravity data suggest that Uranus is more centrally condensed than Neptune. We perform a large suite of high-resolution SPH simulations to investigate whether these differences can be explained by giant impacts. For Uranus, we find that an oblique impact can tilt its spin axis and eject enough material to create a disc where the regular satellites are formed. Some of the discs are massive and extended enough, and consist of enough rocky material to explain the formation of Uranus’ regular satellites. For Neptune, we investigate whether a head-on collision could mix the interior, and lead to an adiabatic temperature profile, which may explain its larger flux and higher moment of inertia value. We find that massive and dense projectiles can penetrate towards the centre and deposit mass and energy in the deep interior, leading to a less centrally concentrated interior for Neptune. We conclude that the dichotomy between the ice giants can be explained by violent impacts after their formation.

The Tectonic Plates are Moving!

2018 ◽  
Author(s):  
Roy Livermore
Keyword(s):  
Plate Tectonics ◽  
First Generation ◽  
Volcanic Eruptions ◽  
Short Article ◽  
Tectonic Plates ◽  
The Earth ◽  
Deep Interior ◽  
Two Generations ◽  
The 1960S

Written in a witty and informal style, this book explains modern plate tectonics in a non-technical manner, showing not only how it accounts for phenomena such as great earthquakes, tsunamis, and volcanic eruptions, but also how it controls conditions at the Earth’s surface, including global geography and climate, making it suitable for life. The book presents the advances that have been made since the establishment of plate tectonics in the 1960s, highlighting, on the fiftieth anniversary of the theory, the contributions of a small number of scientists who have never been widely recognized for their discoveries. Beginning with the publication of a short article in Nature by Vine and Matthews, the book traces the development of plate tectonics through two generations of the theory. First-generation plate tectonics covers the exciting scientific revolution of the 1960s, its heroes, and its villains. The second generation includes the rapid expansions in sonar, satellite, and seismic technologies during the 1980s and 1990s that provided a truly global view of the plates and their motions, and an appreciation of the role of their within the Earth system. Arriving at the cutting edge of the science, the latest results from studies using techniques such as seismic tomography and mineral physics to probe the deep interior are discussed and the prospects for finding plate tectonics on other planets assessed. Ultimately, the book leads to the startling conclusion that, without plate tectonics, the Earth would be as lifeless as Venus.

Unraveling the upper mantle heterogeneity from integrated multi-observable inversions

2020 ◽  
Author(s):  
Javier Fullea ◽  
Sergei Lebedev ◽  
Zdenek Martinec ◽  
Nicolas Celli
Keyword(s):  
Seismic Tomography ◽  
Upper Mantle ◽  
Plate Tectonics ◽  
Seismic Velocity ◽  
Gravity Data ◽  
Density Field ◽  
Seismic Velocities ◽  
Satellite Gravity ◽  
The Earth ◽  
Multiple Data Sets

<p>The lateral and vertical thermochemical heterogeneity in the mantle is a long standing question in geodynamics. The forces that control mantle flow and therefore Plate Tectonics arise from the density and viscosity lateral and vertical variations. A common approach to estimate the density field for geodynamical purposes is to simply convert seismic tomography anomalies sometimes assuming constraints from mineral physics. Such converted density field does not match in general with the observed gravity field, typically predicting anomalies the amplitudes of which are too large. Knowledge on the lateral variations in lithospheric density is essential to understand the dynamic/residual isostatic components of the Earth’s topography linking deep and surface processes. The cooling of oceanic lithosphere, the bathymetry of mid oceanic ridges, the buoyancy and stability of continental cratons or the thermochemical structure of mantle plumes are all features central to Plate Tectonics that are dramatically related to mantle temperature and composition.</p><p><br>Conventional methods of seismic tomography, topography and gravity data analysis constrain distributions of seismic velocity and density at depth, all depending on temperature and composition of the rocks within the Earth. However, modelling and interpretation of multiple data sets provide a multifaceted image of the true thermochemical structure of the Earth that needs to be appropriately and consistently integrated. A simple combination of gravity, petrological and seismic models alone is insufficient due to the non-uniqueness and different sensitivities of these models, and the internal consistency relationships that must connect all the intermediate parameters describing the Earth involved. In fact, global Earth models based on different observables often lead to rather different, even contradictory images of the Earth.</p><p><br> Here we present a new global thermochemical model of the lithosphere-upper mantle (WINTERC-grav) constrained by state-of-the-art global waveform tomography, satellite gravity (geoid and gravity anomalies and gradiometric measurements from ESA's GOCE mission), surface elevation and heat flow data. WINTERC-grav is based upon an integrated geophysical-petrological approach where all relevant rock physical properties modelled (seismic velocities and density) are computed within a thermodynamically self-consistent framework allowing for a direct parameterization of the temperature and composition variables.</p>

scholarly journals The Role of Multiple Giant Impacts in the Formation of the Earth–Moon System

2018 ◽  
Vol 862 (1) ◽  
pp. 5 ◽  
Author(s):  
Robert I. Citron ◽  
Hagai B. Perets ◽  
Oded Aharonson
Keyword(s):  
Moon System ◽  
The Earth ◽  
Giant Impacts

6. The Earth’s heat

2018 ◽  
pp. 92-105
Author(s):  
William Lowrie
Keyword(s):  
Heat Transfer ◽  
Geomagnetic Field ◽  
Plate Tectonics ◽  
Internal Heat ◽  
Outer Core ◽  
Radioactive Isotopes ◽  
Convection Heat ◽  
Crustal Rocks ◽  
Geological Processes ◽  
The Earth

The Earth’s internal heat is its greatest source of energy. It powers global geological processes such as plate tectonics and the generation of the geomagnetic field. ‘The Earth’s heat’ explains that the internal heat arises from two sources: the decay of radioactive isotopes in crustal rocks and the mantle, and primordial heat left over from the planet’s fiery formation. The internal heat has to find its way out of the Earth. The three basic forms of heat transfer are radiation, conduction, and convection. Heat is also transferred in compositional and phase transitions. Heat transport by conduction is most important in solid regions of the Earth, while thermal convection occurs in the viscoelastic mantle and molten outer core.

scholarly journals Mantle Evolution of Asia Inferred from Pb Isotopic Signatures of Sources for Late Phanerozoic Volcanic Rocks

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 739
Author(s):  
Sergei Rasskazov ◽  
Irina Chuvashova ◽  
Tatyana Yasnygina ◽  
Elena Saranina
Keyword(s):  
Upper Mantle ◽  
Lower Mantle ◽  
Volcanic Rocks ◽  
Solid Core ◽  
Magma Ocean ◽  
Low Velocity ◽  
Isotopic Signatures ◽  
Mantle Evolution ◽  
Mantle Sources

We present a systematic study of Pb isotope ages obtained from sources of the late Phanerozoic volcanic rocks from unstable Asia and also volcanic rocks and kimberlites from stable regions of the Siberian and Indian paleocontinents. In the mantle sources, we have recorded events of the Early, Middle, and Late epochs of the Earth’s evolution. Evidence on the Early epoch are preserved in sources of the protolithosphere and viscous lower protomantle likely generated from the Hadean magma ocean about 4.51 and 4.44 Ga and in sources of the viscous upper mantle that acquired low µ and elevated µ (LOMU and ELMU) signatures in the early Archean (4.0–3.7 Ga). The Middle and Late epochs are denoted by sources of the viscous upper mantle that was generated, respectively, in the late Archean-Paleoproterozoic (2.9–2.6 Ga and 2.0–1.8 Ga) and in the Neoproterozoic-late Phanerozoic (0.7–0.6 Ga and < 0.25 Ga). Our results show the specific role of the mantle beneath unstable Asia in terms of globally varied µ signatures and the same mantle epochs in sources of the late Phanerozoic volcanic rocks and kimberlites from stable regions of the Siberian and Indian paleocontinents, but with high μ (HIMU) signatures that are distributed worldwide and explained by sulfide sequestration of Pb from the mantle to the core. We refer the LOMU-ELMU mantle sources to the Asian high-velocity lower mantle domain and propose that the HIMU generating processes were focused mainly in the South Pacific and African low-velocity lower mantle domains in the Middle Mantle Epoch of the Earth’s evolution due to influence of the unbalanced solid core.

A Discussion on the measurement and interpretation of changes of strain in the Earth - Arrangement of convection in the Earth by lunar gravity

1973 ◽  
Vol 274 (1239) ◽  
pp. 397-407 ◽  
Keyword(s):  
Angular Velocity ◽  
Upper Mantle ◽  
Internal Heat ◽  
Seafloor Spreading ◽  
High Latitudes ◽  
Lunar Gravity ◽  
The Earth ◽  
Low Latitudes

Earth strain is found to have dependence on latitude. The possibility is explored that the external gravitational couple is a factor in tectonism . Evidence suggests that where extension is induced in a layer in which melting is limited by pressure, liquefaction and upwelling result. It is then to be expected that the Earth’s internal heat is dissipated by convection ordered (but not caused) by the tidal couple. Upwelling takes place in high latitudes and in the ocean basins and is marked by seafloor spreading. Replacement at depth is effected in low latitudes, at the site of geoidal highs and deepseated seismicity. A n excess in the equatorial potential is associated with the excess of deformation in low latitudes. There then seems no reason to suppose that convection is confined to the upper mantle. The effect at surface is that the lithosphere is displaced west, at an angular velocity greatest at the Equator and varying regionally. As a result this shell segments, and the segments rotate and interact.

Reading the stripes: offshore discoveries in plate tectonics with examples from eastern Canada

1993 ◽  
Vol 30 (2) ◽  
pp. 261-277 ◽  
Author(s):  
Jacob Verhoef ◽  
Walter R. Roest
Keyword(s):  
Plate Tectonics ◽  
Sedimentary Basins ◽  
Geological Survey ◽  
Continental Margins ◽  
Eastern Canada ◽  
Data Set ◽  
Grand Banks ◽  
The Earth ◽  
Wide Acceptance

The emergence and wide acceptance of plate tectonics has had a profound influence on the way we look at the Earth. Starting as a theory to explain similarities in coast lines across the Atlantic, plate tectonics has become a unifying theory in the earth sciences. In this paper, we describe the role of staff of the Geological Survey of Canada in the developing and refining of this theory. At the same time, we illustrate the effect plate tectonics has had on our understanding of the evolution of offshore eastern Canada. Of critical importance in this development was the unique data set collected by systematic surveying of this region, largely by the Geological Survey of Canada, making the Grand Banks of Newfoundland one of the best-studied offshore areas in the world. Plate tectonic theory not only offers a framework for the evolution of ocean basins, continental margins, and their sedimentary basins, but also for the assemblage of continents.

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