Highly reducing conditions during core formation on Mercury: Implications for internal structure and the origin of a magnetic field

Malavergne, Valérie; Toplis, Michael J.; Berthet, S.; Jones, J. H.

doi:10.1016/j.icarus.2009.09.001

Cited by 108 publications

(173 citation statements)

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“…In silicate materials, major elements are usually considered to occur as oxides. However, under the reducing conditions that prevail on Mercury, estimated to be between 2.6 and 6.5 log units below the iron-wüstite buffer (Malavergne et al, 2010;Zolotov, 2011;McCubbin et al, 2012), iron occurs mainly as a metal phase or as a sulfide. Low-and high-pressure partial melting experiments at low fO 2 on the Indarch enstatite chondrite (McCoy et al, 1999;Berthet et al, 2009), a potential building block of Mercury (Wasson, 1988;Brown and Elkins-Tanton, 2009), have shown that immiscible metallic and sulfide melts are in equilibrium with the silicate melt.…”

Section: Surface Compositions: Calculations and Assumptionsmentioning

confidence: 99%

“…Some volatile elements (K and S) are not depleted and the low FeO content of the surface points to highly reduced conditions (Wadhwa, 2008; Zolotov, 2011;McCubbin et al, 2012). This suggests that chondritic materials are probably the building blocks of the planet, possibly either enstatite chondrite or bencubbinite (Wasson, 1988;Taylor and Scott, 2003;Malavergne et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

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Phase equilibria of ultramafic compositions on Mercury and the origin of the compositional dichotomy

Charlier

Grove

Zuber

2013

Earth and Planetary Science Letters

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a b s t r a c tMeasurements of major element ratios obtained by the MESSENGER spacecraft using x-ray fluorescence spectra are used to calculate absolute element abundances of lavas at the surface of Mercury. We discuss calculation methods and assumptions that take into account the distribution of major elements between silicate, metal, and sulfide components and the potential occurrence of sulfide minerals under reduced conditions. These first compositional data, which represent large areas of mixed highreflectance volcanic plains and low-reflectance materials and do not include the northern volcanic plains, share common silica-and magnesium-rich characteristics. They are most similar to terrestrial volcanic rocks known as basaltic komatiites. Two compositional groups are distinguished by the presence or absence of a clinopyroxene component. Melting experiments at one atmosphere on the average compositions of each of the two groups constrain the potential mineralogy at Mercury's surface, which should be dominated by orthopyroxene (protoenstatite and orthoenstatite), plagioclase, minor olivine if any, clinopyroxene (augite), and tridymite. The two compositional groups cannot be related to each other by any fractional crystallization process, suggesting differentiated source compositions for the two components and implying multi-stage differentiation and remelting processes for Mercury. Comparison with high-pressure phase equilibria supports partial melting at pressure o10 kbar, in agreement with last equilibration of the melts close to the crust-mantle boundary with two different mantle lithologies (harzburgite and lherzolite). Magma ocean crystallization followed by adiabatic decompression of mantle layers during cumulate overturn and/or convection would have produced adequate conditions to explain surface compositions. The surface of Mercury is not an unmodified quenched crust of primordial bulk planetary composition. Ultramafic lavas from Mercury have high liquidus temperatures (1450-1350 1C) and very low viscosities, in accordance with the eruption style characterized by flooding of pre-existing impact craters by lava and absence of central volcanoes.

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Section: Surface Compositions: Calculations and Assumptionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Phase equilibria of ultramafic compositions on Mercury and the origin of the compositional dichotomy

Charlier

Grove

Zuber

2013

Earth and Planetary Science Letters

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“…We made the assumption that Mercury formed by accretion of metal-rich chondritic building blocks (enstatite chondrites and/or bencubbinite chondrites; Malavergne et al, 2010Malavergne et al, , 2014Zolotov et al, 2013). We used average sulfide modes (10.0 ± 2.50 wt.%; Jarosewich, 1990;Javoy et al, 2010) and compositions (∼ FeS with 37.0 ± 1.5 wt.% S; Javoy et al, 2010) in EH and CB meteorites and calculated that Mercury may contain 2.7-4.6 wt.% S with the highest probability lying in the range of 3.8 ± 0.5 wt.% S. The exact nature of Mercurian building blocks is however unimportant for the following discussion because all chondritic materials have high S content (∼2-5 wt.% S; Fig.…”

Section: Sulfur Content Of the Mantle And The Corementioning

confidence: 99%

“…The high sulfur concentrations in lavas, together with their low Fe contents and the large metal/silicate ratio of Mercury are strong evidence for accretion and differentiation of the planet under highly reducing conditions (< IW-3; IW = iron-wüstite oxygen fugacity buffer; Malavergne et al, 2010;McCubbin et al, 2012;Zolotov et al, 2013). However, any interpretation of magmatic processes on Mercury and, in particular, the behavior of sulfur in magmas are presently very difficult because of the very limited number of experimental studies performed under oxygen fugacity conditions relevant to Mercury (McCoy et al, 1999;Berthet et al, 2009;Chabot et al, 2014;Malavergne et al, 2014;Vander Kaaden and McCubbin, 2016).…”

Section: Introductionmentioning

confidence: 99%

Sulfur solubility in reduced mafic silicate melts: Implications for the speciation and distribution of sulfur on Mercury

Namur

Charlier

Holtz

et al. 2016

Earth and Planetary Science Letters

118

160

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Chemical data from the MESSENGER spacecraft revealed that surface rocks on Mercury are unusually enriched in sulfur compared to samples from other terrestrial planets. In order to understand the speciation and distribution of sulfur on Mercury, we performed high temperature (1200-1750 • C), lowto high-pressure (1 bar to 4 GPa) experiments on compositions representative of Mercurian lavas and on the silicate composition of an enstatite chondrite. We equilibrated silicate melts with sulfide and metallic melts under highly reducing conditions (IW-1.5 to IW-9.4; IW = iron-wüstite oxygen fugacity buffer). Under these oxygen fugacity conditions, sulfur dissolves in the silicate melt as S 2− and forms complexes with Fe 2+ , Mg 2+ and Ca 2+ . The sulfur concentration in silicate melts at sulfide saturation (SCSS) increases with increasing reducing conditions (from <1 wt.% S at IW-2 to >10 wt.% S at IW-8) and with increasing temperature. Metallic melts have a low sulfur content which decreases from 3 wt.% at IW-2 to 0 wt.% at IW-9. We developed an empirical parameterization to predict SCSS in Mercurian magmas as a function of oxygen fugacity ( f O 2 ), temperature, pressure and silicate melt composition. SCSS being not strictly a redox reaction, our expression is fully valid for magmatic systems containing a metal phase. Using physical constraints of the Mercurian mantle and magmas as well as our experimental results, we suggest that basalts on Mercury were free of sulfide globules when they erupted. The high sulfur contents revealed by MESSENGER result from the high sulfur solubility in silicate melt at reducing conditions. We make the realistic assumption that the oxygen fugacity of mantle rocks was set during equilibration of the magma ocean with the core and/or that the mantle contains a minor metal phase and combine our parameterization of SCSS with chemical data from MESSENGER to constrain the oxygen fugacity of Mercury's interior to IW-5.4 ± 0.4. We also calculate that the mantle of Mercury contains 7-11 wt.% S and that the metallic core of the planet has little sulfur (<1.5 wt.% S). The external part of the Mercurian core is likely to be made up of a thin (<90 km) FeS layer.

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“…Bottom: models of planetary interiors for a planetesimal (left) and for Mercury (right, adapted from Malavergne et al (2010)). -S-Si (droite, données de Sanloup and Fei (2004) et Malavergne et al (2007) Mercure (droite, adaptédeMalavergneetal.(2010)).…”

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confidence: 99%

High-pressure experimental geosciences: state of the art and prospects

Sanloup¹

2012

Bulletin De La Société Géologique De France

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International audienceThis paper aims at reviewing the current advancements of high pressure experimental geosciences. The an- gle chosen is that of in situ measurements at the high pressure (P) and high temperature (T) conditions relevant of the deep Earth and planets, measurements that are often carried out at large facilities (X-ray synchrotrons and neutron sources). Rather than giving an exhaustive catalogue, four main active areas of research are chosen: the latest advance- ments on deep Earth mineralogy, how to probe the properties of melts, how to probe Earth dynamics, and chemical reac- tivity induced by increased P-T conditions. For each area, techniques are briefly presented and selected examples illustrate their potentials, and what that tell us about the structure and dynamics of the planet

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Highly reducing conditions during core formation on Mercury: Implications for internal structure and the origin of a magnetic field

Cited by 108 publications

References 63 publications

Phase equilibria of ultramafic compositions on Mercury and the origin of the compositional dichotomy

Phase equilibria of ultramafic compositions on Mercury and the origin of the compositional dichotomy

Sulfur solubility in reduced mafic silicate melts: Implications for the speciation and distribution of sulfur on Mercury

High-pressure experimental geosciences: state of the art and prospects

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