Chemical heterogeneity on Mercury's surface revealed by the MESSENGER X‐Ray Spectrometer

Weider, S. Z.; Nittler, L. R.; Starr, R.; McCoy, Timothy J.; Stockstill-Cahill, K. R.; Byrne, P. K.; Denevi, Brett W.; Head, J. W.; Solomon, Sean C.

doi:10.1029/2012je004153

Cited by 162 publications

(195 citation statements)

References 80 publications

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“…Keil, 1968;Larimer and Ganapathy, 1987). The correlation between Ca and S has been further corroborated by more recent data (Weider et al, 2012).…”

Section: The Roles Of Sulfur and Iron Metalsupporting

confidence: 71%

“…More data will also assist in the identification of the speciation and distribution of sulfide. For example, the correlation between sulfide and calcium (Nittler et al, 2011;Weider et al, 2012) needs more detailed study.…”

Section: Discussionmentioning

confidence: 99%

“…New data published by Weider et al (2012) expand the database of Nittler et al (2011). Interestingly, Weider et al (2012) still identify two clusters of data points for the older terrain (excluding the Northern plains).…”

Section: Compositional Variation and Terrains On Mercurymentioning

confidence: 99%

“…Interestingly, Weider et al (2012) still identify two clusters of data points for the older terrain (excluding the Northern plains). The dataset also extends to compositions with higher Mg/Si up to 0.8 compared to 0.6 in Nittler et al (2011).…”

Section: Compositional Variation and Terrains On Mercurymentioning

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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“…Keil, 1968;Larimer and Ganapathy, 1987). The correlation between Ca and S has been further corroborated by more recent data (Weider et al, 2012).…”

Section: The Roles Of Sulfur and Iron Metalsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 99%

Section: Compositional Variation and Terrains On Mercurymentioning

confidence: 99%

Section: Compositional Variation and Terrains On Mercurymentioning

confidence: 99%

See 2 more Smart Citations

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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“…Silicate compositions were chosen to match (1) lavas of the Northern Volcanic Plains (NVP), (2) the high-Mg terrane (HMg) of the IcP-HCT and (3) a composition representative of the silicate fraction of an enstatite chondrite (EH). NVP and HMg compositions are based on geochemical data presented by Weider et al (2012). For NVP, we used 34 X-Ray Spectroscopy (XRS) measurements and calculated median values for the Mg/Si, Al/Si and Ca/Si ratios and re-calculated the compositions on an oxide basis.…”

Section: Choice and Preparation Of Starting Compositionsmentioning

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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The tides of Mercury and possible implications for its interior structure

et al. 2014

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Key Points:• We present models of the tidal deformation of Mercury based on MESSENGER results • Tides are sensitive to size and density of the core and rheology of outer shell • The presence of a FeS layer would increase the tidal response AbstractThe combination of the radio tracking of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft and Earth-based radar measurements of the planet's spin state gives three fundamental quantities for the determination of the interior structure of Mercury: mean density , moment of inertia C, and moment of inertia of the outer solid shell C m . This work focuses on the additional information that can be gained by a determination of the change in gravitational potential due to planetary tides, as parameterized by the tidal potential Love number k 2 . We investigate the tidal response for sets of interior models that are compatible with the available constraints ( , C, and C m ). We show that the tidal response correlates with the size of the liquid core and the mean density of material below the outer solid shell and that it is affected by the rheology of the outer solid shell of the planet, which depends on its temperature and mineralogy. For a mantle grain size of 1 cm, we calculate that the tidal k 2 of Mercury is in the range 0.45 to 0.52. Some of the current models for the interior structure of Mercury are compatible with the existence of a solid FeS layer at the top of the core. Such a layer, if present, would increase the tidal response of the planet.

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Chemical heterogeneity on Mercury's surface revealed by the MESSENGER X‐Ray Spectrometer

Cited by 162 publications

References 80 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

The tides of Mercury and possible implications for its interior structure

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