Melting processes and mantle sources of lavas on Mercury

Namur, Olivier; Collinet, Max; Charlier, Bernard; Grove, T. L.; Holtz, François; McCammon, Catherine

doi:10.1016/j.epsl.2016.01.030

Cited by 77 publications

(113 citation statements)

References 62 publications

(116 reference statements)

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“…This implies that sulfide minerals were not entirely exhausted during the partial melting process. This is in qualitative agreement with chemical data from MESSENGER which show that rocks from the HMg terrane, which require the highest degree of mantle melting (>40%), are not depleted in sulfur compared to lavas from IcP-HCT (<35% of melting), SP and NVP (<30% of melting; Namur et al, 2016;Vander Kaaden and McCubbin, 2016). It is therefore reasonable to assume that Mercurian lavas were still at sulfide saturation when they erupted at the surface of the planet.…”

Section: Oxygen Fugacity Conditions During Mantle Melting and Basaltisupporting

confidence: 77%

“…Assuming that Mercury differentiated through the formation of a magma ocean (Brown and Elkins-Tanton, 2009;Charlier et al, 2013;Chabot et al, 2014), early differentiation of the planet did set the sulfur content of the core and the lherzolitic mantle. Partial melting of the mantle then produced the secondary crust Namur et al, 2016). In the following, we discuss the mechanism of sulfur migration from the Mercurian mantle to the crust.…”

Section: Discussionmentioning

confidence: 99%

“…The use of Eq. (10) is appropriate because some surface melts were produced at the mantle-core interface indicating that the mantle source was metal saturated (Namur et al, 2016) and Mercurian lavas contain some Fe, possibly included in Fe-silicides . We finally discuss the likely distribution of sulfur between the core and mantle on Mercury.…”

Section: Discussionmentioning

confidence: 99%

“…With increasing degree of mantle melting, the capillary pressure decreases and sulfide melt droplets eventually become mobile. This however requires a degree of melting exceeding 40 vol.% (Holzheid et al, 2000), which is higher than the melt fraction needed to produce the S-rich lavas from NVP, SP and IcP-HCT (Namur et al, 2016). In addition, coalescence of sulfide droplets through Ostwald ripening would require extremely low abundances of sulfides and a mantle with unrealistically large (cm-scale) crystals before sulfide melts become effectively mobile (Mungall and Su, 2005).…”

Section: Transport Of Sulfur From the Mantle To The Mercurian Surfacementioning

confidence: 99%

“…It is made of a very large core (∼65 wt.% of the planet; ) and a thin mantle (420 ± 30 km; Hauck et al, 2013;Padovan et al, 2015) dominated by olivine, orthopyroxene, clinopyroxene, ± spinel and feldspar Charlier et al, 2013;Namur et al, 2016;Vander Kaaden and McCubbin, 2016). Building blocks of Mercury could be compositionally close to enstatite chondrite or bencubbinite chondrite mete- The data for the Mercurian crust were calculated using the MESSENGER data presented by Weider et al (2015).…”

Section: Introductionmentioning

confidence: 99%

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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

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106

156

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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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Section: Oxygen Fugacity Conditions During Mantle Melting and Basaltisupporting

confidence: 77%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Transport Of Sulfur From the Mantle To The Mercurian Surfacementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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

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106

156

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A whole new Mercury: MESSENGER reveals a dynamic planet at the last frontier of the inner solar system

Johnson

Hauck

2016

JGR Planets

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The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission yielded a wealth of information about the innermost planet. For the first time, visible images of the entire planet, absolute altimetry measurements and a global gravity field, measurements of Mercury's surface composition, magnetic field, exosphere, and magnetosphere taken over more than four Earth years are available. From these data, two overarching themes emerge. First, multiple data sets and modeling efforts point toward a dynamic ancient history. Signatures of graphite in the crust suggest solidification of an early magma ocean, image data show extensive volcanism and tectonic features indicative of subsequent global contraction, and low‐altitude measurements of magnetic fields reveal an ancient magnetic field. Second, the present‐day Mercury environment is far from quiescent. Convective motions in the outer core support a modern magnetic field whose strength and geometry are unique among planets with global magnetic fields. Furthermore, periodic and aperiodic variations in the magnetosphere and exosphere have been observed, some of which couple to the surface and the planet's deep interior. Finally, signatures of geologically recent volatile activity at the surface have been detected. Mercury's early history and its present‐day environment have common elements with the other inner solar system bodies. However, in each case there are also crucial differences and these likely hold the key to further understanding of Mercury and terrestrial planet evolution. MESSENGER's exploration of Mercury has enabled a new view of the innermost planet, and more importantly has set the stage for much‐needed future exploration.

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Experimental constraints on the rheology, eruption, and emplacement dynamics of analog lavas comparable to Mercury's northern volcanic plains

et al. 2017

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We present new viscosity measurements of a synthetic silicate system considered an analogue for the lava erupted on the surface of Mercury. In particular, we focus on the northern volcanic plains (NVP), which correspond to the largest lava flows on Mercury and possibly in the Solar System. High‐temperature viscosity measurements were performed at both superliquidus (up to 1736 K) and subliquidus conditions (1569–1502 K) to constrain the viscosity variations as a function of crystallinity (from 0 to 28%) and shear rate (from 0.1 to 5 s−1). Melt viscosity shows moderate variations (4–16 Pa s) in the temperature range of 1736–1600 K. Experiments performed below the liquidus temperature show an increase in viscosity as shear rate decreases from 5 to 0.1 s−1, resulting in a shear thinning behavior, with a decrease in viscosity of ~1 log unit. The low viscosity of the studied composition may explain the ability of NVP lavas to cover long distances, on the order of hundreds of kilometers in a turbulent flow regime. Using our experimental data we estimate that lava flows with thickness of 1, 5, and 10 m are likely to have velocities of 4.8, 6.5, and 7.2 m/s, respectively, on a 5° ground slope. Numerical modeling incorporating both the heat loss of the lavas and its possible crystallization during emplacement allows us to infer that high effusion rates (>10,000 m3/s) are necessary to cover the large distances indicated by satellite data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft.

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Melting processes and mantle sources of lavas on Mercury

Cited by 77 publications

References 62 publications

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

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

A whole new Mercury: MESSENGER reveals a dynamic planet at the last frontier of the inner solar system

Experimental constraints on the rheology, eruption, and emplacement dynamics of analog lavas comparable to Mercury's northern volcanic plains

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