scholarly journals Initiation of plate tectonics from post-magma ocean thermochemical convection

2014 ◽  
Vol 119 (11) ◽  
pp. 8538-8561 ◽  
Author(s):  
Bradford J. Foley ◽  
David Bercovici ◽  
Linda T. Elkins-Tanton
Keyword(s):  
Plate Tectonics ◽  
Magma Ocean ◽  
Thermochemical Convection

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>

2. First rocks on a dead Earth

2016 ◽  
pp. 13-28
Author(s):  
Jan Zalasiewicz
Keyword(s):  
Cooling Rate ◽  
Subduction Zones ◽  
Plate Tectonics ◽  
Igneous Rocks ◽  
Magma Ocean ◽  
Plate Collision ◽  
Ocean Ridges ◽  
Different Types ◽  
Fractional Melting

‘First rocks on a dead Earth’ describes the formation of the planet Earth from the collision of the precursor planets Tellus and Theia. The surface of the newly born Earth had a surface magma ocean. As this magma cooled, the first minerals formed. The earliest rocks on Earth date back to the Archaeon Eon. During that time, plate tectonics started up, which determined the nature of all subsequent rocks on Earth. The processes of fractional melting and impact of cooling rate on crystal sizes is explained along with the different types of igneous rocks—basalts, andesites, diorites, rhyolites, and granites—formed at mid-ocean ridges, subduction zones, and plate collision zones.

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’.

scholarly journals Hydrated Peridotite – Basaltic Melt Interaction Part I: Planetary Felsic Crust Formation at Shallow Depth

2021 ◽  
Vol 9 ◽  
Author(s):  
Anastassia Y. Borisova ◽  
Nail R. Zagrtdenov ◽  
Michael J. Toplis ◽  
Wendy A. Bohrson ◽  
Anne Nédélec ◽  
...  
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Mafic Magma ◽  
Aqueous Fluid ◽  
Early Earth ◽  
Magma Ocean ◽  
Crust Formation ◽  
Basaltic Melt ◽  
Low Pressures ◽  
Direct Melting

Current theories suggest that the first continental crust on Earth, and possibly on other terrestrial planets, may have been produced early in their history by direct melting of hydrated peridotite. However, the conditions, mechanisms and necessary ingredients for this crustal formation remain elusive. To fill this gap, we conducted time-series experiments to investigate the reaction of serpentinite with variable proportions (from 0 to 87 wt%) of basaltic melt at temperatures of 1,250–1,300°C and pressures of 0.2–1.0 GPa (corresponding to lithostatic depths of ∼5–30 km). The experiments at 0.2 GPa reveal the formation of forsterite-rich olivine (Fo90–94) and chromite coexisting with silica-rich liquids (57–71 wt% SiO2). These melts share geochemical similarities with tonalite-trondhjemite-granodiorite rocks (TTG) identified in modern terrestrial oceanic mantle settings. By contrast, liquids formed at pressures of 1.0 GPa are poorer in silica (∼50 wt% SiO2). Our results suggest a new mechanism for the formation of the embryonic continental crust via aqueous fluid-assisted partial melting of peridotite at relatively low pressures (∼0.2 GPa). We hypothesize that such a mechanism of felsic crust formation may have been widespread on the early Earth and, possibly on Mars as well, before the onset of modern plate tectonics and just after solidification of the first ultramafic-mafic magma ocean and alteration of this primitive protocrust by seawater at depths of less than 10 km.

scholarly journals The evolution of plate tectonics

2018 ◽  
Vol 376 (2132) ◽  
pp. 20170406 ◽  
Author(s):  
Robert J. Stern
Keyword(s):  
Plate Tectonics ◽  
Dominant Mode ◽  
Plate Tectonic ◽  
Magma Ocean ◽  
Tectonic Regime ◽  
Climate Crisis ◽  
Earth Dynamics ◽  
Multiple Episodes ◽  
Lines Of Evidence ◽  
Standing Question

To understand how plate tectonics became Earth's dominant mode of convection, we need to address three related problems. (i) What was Earth's tectonic regime before the present episode of plate tectonics began? (ii) Given the preceding tectonic regime, how did plate tectonics become established? (iii) When did the present episode of plate tectonics begin? The tripartite nature of the problem complicates solving it, but, when we have all three answers, the requisite consilience will provide greater confidence than if we only focus on the long-standing question of when did plate tectonics begin? Earth probably experienced episodes of magma ocean, heat-pipe, and increasingly sluggish single lid magmatotectonism. In this effort we should consider all possible scenarios and lines of evidence. As we address these questions, we should acknowledge there were probably multiple episodes of plate tectonic and non-plate tectonic convective styles on Earth. Non-plate tectonic styles were probably dominated by ‘single lid tectonics’ and this evolved as Earth cooled and its lithosphere thickened. Evidence from the rock record indicates that the modern episode of plate tectonics began in Neoproterozoic time. A Neoproterozoic transition from single lid to plate tectonics also explains kimberlite ages, the Neoproterozoic climate crisis and the Neoproterozoic acceleration of evolution. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics’.

How does volcanic outgassing differ on geological time scales between planets with and without plate tectonics?

2021 ◽  
Author(s):  
Lena Noack
Keyword(s):  
Plate Tectonics ◽  
Plate Boundaries ◽  
Magma Ocean ◽  
Geological Time ◽  
Molten Material ◽  
Liquid Form ◽  
Formation Stage ◽  
Harmful Radiation ◽  
Rocky Planets ◽  
Volcanic Outgassing

<div>One of the main factors to assess the possible habitability of a rocky planet (either in or beyond our solar system) is its capability to maintain an atmosphere that allows for moderate temperatures at the surface and would allow water to occur in a liquid form, and that can help shield surface life from harmful radiation.</div> <div>The existence of an atmosphere depends on several factors - possible accretion from the nebula and catastrophic degassing from the crystallizing magma ocean during planet formation, later delivery of volatiles via comets, sinks of atmosphere gases to the surface or to space, and last, but definitely not least, volcanic release of volatiles from the mantle that where stored in the planet's interior during its formation stage.</div> <div>For planets of masses not too different from Earth, volcanic degassing plays a major role for the question if the planet could have an atmosphere. Lower-mass planets might not be able to keep an atmosphere but loose it entirely to space, and much more massive super-Earth planets will likely keep the primordial, catastrophically outgassed atmosphere during magma ocean crystallization, and may never be habitable at their surface due to a thick atmosphere rather comparable to Venus. The "Goldilocks zone" for potentially habitable rocky planets is therefore limited to a range from above Mars' mass to a few Earth masses. However, planets of a few Earth masses may not be able to efficiently outgas volcanic gases, if they are in a stagnant-lid regime. This may be different, though, for planets experiencing plate tectonics like Earth, where hot, molten material reaches the surface at plate boundaries and may therefore build up or replenish an atmosphere. The work presented here compares the efficiency of interior volatile depletion and degassing to the surface for rocky planets of different size and composition, either in the stagnant-lid or in the plate-tectonics regime.</div>

scholarly journals Magma oceans as a critical stage in the tectonic development of rocky planets

2018 ◽  
Vol 376 (2132) ◽  
pp. 20180109 ◽  
Author(s):  
Laura Schaefer ◽  
Linda T. Elkins-Tanton
Keyword(s):  
Plate Tectonics ◽  
Magma Ocean ◽  
Stability Issue ◽  
Tectonic Development ◽  
Magma Oceans ◽  
Set Up ◽  
Almost All ◽  
High Degree ◽  
Rocky Planets ◽  
Earth Dynamics

Magma oceans are a common result of the high degree of heating that occurs during planet formation. It is thought that almost all of the large rocky bodies in the Solar System went through at least one magma ocean phase. In this paper, we review some of the ways in which magma ocean models for the Earth, Moon and Mars match present-day observations of mantle reservoirs, internal structure and primordial crusts, and then we present new calculations for the oxidation state of the mantle produced during the magma ocean phase. The crystallization of magma oceans probably leads to a massive mantle overturn that may set up a stably stratified mantle. This may lead to significant delays or total prevention of plate tectonics on some planets. We review recent models that may help alleviate the mantle stability issue and lead to earlier onset of plate tectonics. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics’.

Mobile or not mobile: exploring the linkage between deep mantle composition and early Earth surface mobility

2020 ◽  
Author(s):  
Keely A. O'Farrell ◽  
Sean Trim ◽  
Samuel Butler
Keyword(s):  
Mantle Convection ◽  
Plate Tectonics ◽  
Numerical Models ◽  
Early Earth ◽  
Surface Dynamics ◽  
Magma Ocean ◽  
Surface Mobility ◽  
Deep Mantle ◽  
Deep Interior ◽  
Tracer Methods

<p>Numerical models of mantle convection help our understanding of the complex feedback between the plates and deep interior dynamics through space and time. Did the early Earth have plate tectonics, a stagnant lid, or something in between? The surface dynamics of the early Earth remain poorly understood. Current numerical models of mantle convection are constrained by present-day observations, but the behavior of the hotter, early Earth prior to the onset of plate tectonics is less certain. The early Earth may have possessed a large hot magma ocean trapped near the core-mantle boundary after formation during differentiation, and likely containing different elements from the surrounding mantle. We examine how composition-dependent properties in the deep mantle affect convection dynamics and surface mobility in high Rayleigh number models featuring plastic yielding. Our Newtonian models indicate that increased conductivity or decreased viscosity flattens basal topography while also increasing the potential for surface yielding. We vary the viscosity, thermal conductivity, and internal heating in a compositionally distinct basal magma ocean and explore the compositional topography, insulation effects and surface stresses for non-Newtonian rheology. Models are run using a variety of crustal compositions, such as the inclusion of primordial continental material before the onset of plate tectonics. We monitor the surface for plate-like behavior. Since convective vigour is very strong in the early Earth, specialized tracer methods are employed for increased accuracy. In our models, Stokes flow solutions are obtained using a multigrid method specifically designed to handle large viscosity contrasts and non-Newtonian rheology.</p>

LLSVPs of primordial origin: Implications for the evolution of plate tectonics

2020 ◽  
Author(s):  
Philipp Hellenkamp ◽  
Claudia Stein ◽  
Ulrich Hansen
Keyword(s):  
Mantle Convection ◽  
Plate Tectonics ◽  
Basal Layer ◽  
Numerical Approach ◽  
Dense Layer ◽  
Magma Ocean ◽  
Strongly Coupled ◽  
Plate Motions ◽  
Core Mantle Boundary ◽  
Lithospheric Plates

<p>Early periods of Earth's history are of great interest for the evolution of plate tectonics. For instance, neither the formation of lithospheric plates nor the nature of Archean plate tectonics is well known. As a remnant of the magma ocean period, a compositionally dense layer at the core-mantle boundary is assumed to interact with the convective flow of the Earth's mantle forming todays LLSVPs. Since plate motions are strongly coupled to the convection of mantle material, stabilizing effects of compositionally dense material have a profound impact on mantle convection and plate tectonics and will be of major importance for its evolution. <br>To investigate the influence of a dense basal layer, we use a numerical approach employing thermo-chemical mantle convection models with self-consistent plate generation. Considering different possible scenarios of the post magma ocean period we analyze the influence of different parameters, i.e. the density contrast between the dense basal material and the ambient mantle and the volume of the enriched layer. <br>Generally we observe that a stagnant lid forms which is initially mobilized episodically before turning to a permanently mobile surface. However, the temporal evolution of the episodic stage is considerably altered due to the presence of dense basal material. The time when an episode occurs, is determined by the mechanism which induces this mobilization. The mechanism itself is controlled by the density and volume of the enriched layer. Therefore, we distinguish between four different initiation mechanisms, which occur for different configurations of the density and volume of enriched material.</p>

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