Melting of MORB at core–mantle boundary

Pradhan, Gopal K.; Fiquet, G.; Siebert, J.; Auzende, Anne-Line; Morard, Guillaume; Antonangeli, Daniele; Garbarino, Gastón

doi:10.1016/j.epsl.2015.09.034

Cited by 77 publications

(84 citation statements)

References 61 publications

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“…The composition of the perovskite-bearing solid phase (all the crystallites of the simulation box have on average the same composition and the same structure) is Ca-rich and is enriched in SiO 2 , TiO 2 , MgO, FeO, Na 2 O, and K 2 O with respect to the MORB original composition while the coexisting melt is depleted in the latter oxides but is enriched in Al 2 O 3 (see Table 2). The finding that the perovskite phase is Ca-rich is in accordance with the observation that Ca-Pv is the liquidus phase of MORB in this T-P range (T > 2473 K and P > 25 GPa) and the fact that the melt is enriched in Al 2 O 3 and depleted in SiO 2 is also in agreement with the observation of Pradhan et al (2015). Nevertheless this Ca-rich perovskite phase is likely metastable and the simulation time necessary to overcome the energy barrier for the system to be restructured in a 5-solid phases is out of reach with our computational resources.…”

Section: Introductionsupporting

confidence: 89%

Properties of magmatic liquids by molecular dynamics simulation: The example of a MORB melt

et al. 2017

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International audienceA new atom-atom interaction potential is introduced for describing by classical molecular dynamics (MD) simulation the physical properties of natural silicate melts. The equation of state, the microscopic structure, the viscosity, the electrical conductivity, and the self-diffusion coefficients of ions in a mid-oceanic ridge basalt (MORB) melt are evaluated by MD over a large range of temperature and pressure (1673-3273 K and 0-60 GPa). A detailed comparison with experimental data shows that the model reproduces the thermodynamic, structural and transport properties of a MORB with an unprecedented accuracy. In particular, it is shown that the MORB melt crystallizes at lower mantle conditions into a perovskite phase whose the equation of state (EOS) is compatible with those proposed in the experimental literature. Moreover, in accordance with experimental findings, the simulation predicts not only that the MORB viscosity exhibits a (slight) minimum with the pressure, but also that the viscosity at high temperature remains very low (<100 mPa.s for T > 2273 K) even at high pressure (up to 40 GPa). However the evolution of the electrical conductivity with temperature and pressure is not always the symmetrical of that of the viscosity. In fact, the relationship between viscosity and electrical conductivity shows a crossover at around 2073 K

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Section: Introductionsupporting

confidence: 89%

Properties of magmatic liquids by molecular dynamics simulation: The example of a MORB melt

et al. 2017

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“…The possible existence of dense silicate melts at or near the CMB has been proposed (e.g., Ohtani 1983; Ohtani and Maeda 2001;Williams and Garnero 1996;Labrosse et al 2007) to explain the anomalous reduction of the seismic wave velocities just above the CMB (e.g., Garnero and Helmberger 1995;Mori and Helmberger 1995). Recent high-pressure melting experiments indicated that such dense silicate melts at the CMB can be generated by partial melting of midocean ridge basalts (MORBs) (Andrault et al 2014;Pradhan et al 2015). The densification in SA1 and SA2, which probably reflects an average Si-O coordination number in excess of 6, occurs at lower pressures than in pure MgSiO 3 glass (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Figure 6 shows the inflection pressure as a function of Al 2 O 3 contents in the SiO 2 -Al 2 O 3 system, indicating a linear relationship. If we assume that an Al 2 O 3 content of~13 mol% may possibly be included in partial melts of MORBs generated at around 100 GPa (Pradhan et al 2015), the inflection pressure is expected to be 124 GPa corresponding to a depth of~2690 km. The silicate melts generated by the partial melting of MORBs might thus undergo a structural transformation involving possible densification changes related to Si-O coordination states at depths of around~2690 km, which is clearly shallower than the CMB.…”

Section: Resultsmentioning

confidence: 99%

Ultrahigh-pressure acoustic wave velocities of SiO2-Al2O3 glasses up to 200 GPa

Ohira

Murakami

Kohara

et al. 2016

Prog. in Earth and Planet. Sci.

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Extensive experimental studies on the structure and density of silicate glasses as laboratory analogs of natural silicate melts have attempted to address the nature of dense silicate melts that may be present at the base of the mantle. Previous ultrahigh-pressure experiments, however, have been performed on simple systems such as SiO 2 or MgSiO 3 , and experiments in more complex system have been conducted under relatively low-pressure conditions below 60 GPa. The effect of other metal cations on structural changes that occur in dense silicate glasses under ultrahigh pressures has been poorly understood. Here, we used a Brillouin scattering spectroscopic method up to pressures of 196.9 GPa to conduct in situ high-pressure acoustic wave velocity measurements of SiO 2 -Al 2 O 3 glasses in order to understand the effect of Al 2 O 3 on pressure-induced structural changes in the glasses as analogs of aluminosilicate melts. From 10 to 40 GPa, the transverse acoustic wave velocity (V S ) of Al 2 O 3 -rich glass (SiO 2 + 20. 5 mol% Al 2 O 3 ) was greater than that of Al 2 O 3 -poor glass (SiO 2 + 3.9 mol% Al 2 O 3 ). This result suggests that SiO 2 -Al 2 O 3 glasses with higher proportions of Al ions with large oxygen coordination numbers (5 and 6) become elastically stiffer up to 40 GPa, depending on the Al 2 O 3 content, but then soften above 40 GPa. At pressures from 40 to~100 GPa, the increase in V S with increasing pressure became less steep than below 40 GPa. Abovẽ 100 GPa, there were abrupt increases in the P-V S gradients (dV S /dP) at 130 GPa in Al 2 O 3 -poor glass and at 116 GPa in Al 2 O 3 -rich glass. These changes resemble previous experimental results on SiO 2 glass and MgSiO 3 glass. Given that changes of dV S /dP have commonly been related to changes in the Si-O coordination states in the glasses, our results, therefore, may indicate a drastic structural transformation in SiO 2 -Al 2 O 3 glasses above 116 GPa, possibly associated with an average Si-O coordination number change to higher than 6. Compared to previous acoustic wave velocity data on SiO 2 and MgSiO 3 glasses, Al 2 O 3 appears to promote a lowering of the pressure at which the abrupt increase of dV S /dP is observed. This suggests that the Al 2 O 3 in silicate melts may help to stabilize those melts gravitationally in the lower mantle.

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“…A strong partitioning of Fe into the partial melts at lowermost mantle conditions (Tateno et al 2014;Pradhan et al 2015) will make the partially molten regions denser than the surrounding mantle, including the LLSVP material.…”

Section: Compositional Asymmetry Of Plumes and Ultra-low Velocity Zonesmentioning

confidence: 99%

Earth evolution and dynamics—a tribute to Kevin Burke

et al. 2016

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Kevin Burke's original and thought-provoking contributions have been published steadily for the past sixty years, and more than a decade ago he set out to resolve how plate tectonics and mantle plumes interact by proposing a simple conceptual model, which we will refer to as "the Burkian Earth". On the Burkian Earth, mantle plumes take us from the deepest mantle to sub-lithospheric depths, where partial melting occurs, and to the surface, where hotspot lavas erupt today, and where large igneous provinces and kimberlites have erupted episodically in the past. The arrival of a plume head contributes to continental break-up and punctuates plate tectonics by creating and modifying plate boundaries. Conversely, plate tectonics makes an essential contribution to the mantle through subduction. Slabs restore mass to the lowermost mantle and are the triggering mechanism for plumes that rise from the margins of large-scale low shear-wave velocity structures in the lowermost mantle, that Kevin christened TUZO and JASON. Situated just above the core-mantle boundary beneath Africa and the Pacific, these are two stable and antipodal thermochemical piles, which Kevin reasons represent the immediate after-effect of the moon-forming event and the final magma ocean crystallization.

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Melting of MORB at core–mantle boundary

Cited by 77 publications

References 61 publications

Properties of magmatic liquids by molecular dynamics simulation: The example of a MORB melt

Properties of magmatic liquids by molecular dynamics simulation: The example of a MORB melt

Ultrahigh-pressure acoustic wave velocities of SiO2-Al2O3 glasses up to 200 GPa

Earth evolution and dynamics—a tribute to Kevin Burke

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