TY - JOUR
T1 - On the chemistry of mantle and magmatic volatiles on Mercury
AU - Zolotov, Mikhail
N1 - Funding Information:
The manuscript is benefited from comments from Steven Lehner, Bruce Fegley, and an anonymous reviewer. This work is supported by grants from NSF Planetary Astronomy, NASA Cosmochemistry, and NASA Planetary Geology and Geophysics programs.
PY - 2011/3
Y1 - 2011/3
N2 - The surface of Mercury contains ancient volcanic features and signs of pyroclastic activity related to unknown magmatic volatiles. Here, the nature of possible magmatic volatiles (H, S, C, Cl, and N) is discussed in the contexts of formation and evolution of the planet, composition and redox state of its mantle, solubility in silicate melts, chemical mechanisms of magma degassing, and thermochemical equilibria in magma and volcanic gases. The low-FeO content in surface materials (<6wt%) evaluated with remote sensing methods corresponds to less than 2.3 fO2 log units below the iron-wüstite buffer. These redox conditions imply restricted involvement of hydrous species in nebular and accretion processes, and a limited loss of S, Cl, and N during formation and evolution of the planet. Reduced conditions correspond to high solubilities of these elements in magma and do not favor degassing. Major degassing and pyroclastic activity would require oxidation of melts in near-surface conditions. Low-pressure oxidation of graphite in moderately oxidized magmas causes formation of low-solubility CO. Decompression of reduced N-saturated melts involves oxidation of nitride melt complexes and could cause N2 degassing. Putative assimilation of oxide (FeO, TiO2, and SiO2) rich rocks in magma chambers could have caused major degassing through oxidation of graphite and S-, Cl- and N-bearing melt complexes. However, crustal rocks may never have been oxidized, and sulfides, graphite, chlorides, and nitrides could remain in crystallized rocks. Chemical equilibrium models show that N2, CO, S2, CS2, S2Cl, Cl, Cl2, and COS could be among the most abundant volcanic gases on Mercury. Though, these speciation models are restricted by uncertain redox conditions, unknown volatile content in magma, and the adopted chemical degassing mechanism.
AB - The surface of Mercury contains ancient volcanic features and signs of pyroclastic activity related to unknown magmatic volatiles. Here, the nature of possible magmatic volatiles (H, S, C, Cl, and N) is discussed in the contexts of formation and evolution of the planet, composition and redox state of its mantle, solubility in silicate melts, chemical mechanisms of magma degassing, and thermochemical equilibria in magma and volcanic gases. The low-FeO content in surface materials (<6wt%) evaluated with remote sensing methods corresponds to less than 2.3 fO2 log units below the iron-wüstite buffer. These redox conditions imply restricted involvement of hydrous species in nebular and accretion processes, and a limited loss of S, Cl, and N during formation and evolution of the planet. Reduced conditions correspond to high solubilities of these elements in magma and do not favor degassing. Major degassing and pyroclastic activity would require oxidation of melts in near-surface conditions. Low-pressure oxidation of graphite in moderately oxidized magmas causes formation of low-solubility CO. Decompression of reduced N-saturated melts involves oxidation of nitride melt complexes and could cause N2 degassing. Putative assimilation of oxide (FeO, TiO2, and SiO2) rich rocks in magma chambers could have caused major degassing through oxidation of graphite and S-, Cl- and N-bearing melt complexes. However, crustal rocks may never have been oxidized, and sulfides, graphite, chlorides, and nitrides could remain in crystallized rocks. Chemical equilibrium models show that N2, CO, S2, CS2, S2Cl, Cl, Cl2, and COS could be among the most abundant volcanic gases on Mercury. Though, these speciation models are restricted by uncertain redox conditions, unknown volatile content in magma, and the adopted chemical degassing mechanism.
KW - Cosmochemistry
KW - Mercury, Interior
KW - Mercury, Surface
KW - Volcanism
UR - http://www.scopus.com/inward/record.url?scp=79952008878&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=79952008878&partnerID=8YFLogxK
U2 - 10.1016/j.icarus.2010.12.014
DO - 10.1016/j.icarus.2010.12.014
M3 - Article
AN - SCOPUS:79952008878
SN - 0019-1035
VL - 212
SP - 24
EP - 41
JO - Icarus
JF - Icarus
IS - 1
ER -