TY - JOUR
T1 - Aqueous fluid composition in CI chondritic materials
T2 - Chemical equilibrium assessments in closed systems
AU - Zolotov, Mikhail
N1 - Funding Information:
The work is benefited from review comments of Michael Petaev and from collaboration with Mikhail Mironenko who chiefly contributed to the code development. This work is supported by Grants from NASA Cosmochemistry, Outer Planet Research, Planetary Geology and Geophysics programs, and NASA Astrobiology Institute.
PY - 2012/8
Y1 - 2012/8
N2 - Solids of nearly solar composition have interacted with aqueous fluids on carbonaceous asteroids, icy moons, and trans-neptunian objects. These processes altered mineralogy of accreted materials together with compositions of aqueous and gaseous phases. We evaluated chemistry of aqueous solutions coexisted with CI-type chondritic solids through calculations of chemical equilibria in closed water-rock-gas systems at different compositions of initial fluids, water/rock mass ratios (0.1-1000), temperatures (<350°C), and pressures (<2kbars). The calculations show that fluid compositions are mainly affected by solubilities of solids, the speciation of chlorine in initial water-rock mixtures, and the occurrence of Na-bearing secondary minerals such as saponite. The major species in modeled alkaline solutions are Na +, Cl -, CO32-,HCO3-, K +, OH -, H 2, and CO 2. Aqueous species of Mg, Fe, Ca, Mn, Al, Ni, Cr, S, and P are not abundant in these fluids owing to low solubility of corresponding solids. Typical NaCl type alkaline fluids coexist with saponite-bearing mineralogy that usually present in aqueously altered chondrites. A common occurrence of these fluids is consistent with the composition of grains emitted from Enceladus. Na-rich fluids with abundant CO32-,HCO3-, and OH - anions coexist with secondary mineralogy depleted in Na. The Na 2CO 3 and NaHCO 3 type fluids could form via accretion of cometary ices. NaOH type fluids form in reduced environments and may locally occur on parent bodies of CR carbonaceous chondrites. Supposed melting of accreted HCl-bearing ices leads to early acidic fluids enriched in Mg, Fe and other metals, consistent with signs of low-pH alteration in chondrites. Neutralization of these solutions leads to alkaline Na-rich fluids. Sulfate species have negligible concentrations in closed systems, which remain reduced, especially at elevated pressures created by forming H 2 gas. Hydrogen, CO 2, and H 2O dominate in the gaseous phase, though the abundance of methane cannot be fairly estimated.
AB - Solids of nearly solar composition have interacted with aqueous fluids on carbonaceous asteroids, icy moons, and trans-neptunian objects. These processes altered mineralogy of accreted materials together with compositions of aqueous and gaseous phases. We evaluated chemistry of aqueous solutions coexisted with CI-type chondritic solids through calculations of chemical equilibria in closed water-rock-gas systems at different compositions of initial fluids, water/rock mass ratios (0.1-1000), temperatures (<350°C), and pressures (<2kbars). The calculations show that fluid compositions are mainly affected by solubilities of solids, the speciation of chlorine in initial water-rock mixtures, and the occurrence of Na-bearing secondary minerals such as saponite. The major species in modeled alkaline solutions are Na +, Cl -, CO32-,HCO3-, K +, OH -, H 2, and CO 2. Aqueous species of Mg, Fe, Ca, Mn, Al, Ni, Cr, S, and P are not abundant in these fluids owing to low solubility of corresponding solids. Typical NaCl type alkaline fluids coexist with saponite-bearing mineralogy that usually present in aqueously altered chondrites. A common occurrence of these fluids is consistent with the composition of grains emitted from Enceladus. Na-rich fluids with abundant CO32-,HCO3-, and OH - anions coexist with secondary mineralogy depleted in Na. The Na 2CO 3 and NaHCO 3 type fluids could form via accretion of cometary ices. NaOH type fluids form in reduced environments and may locally occur on parent bodies of CR carbonaceous chondrites. Supposed melting of accreted HCl-bearing ices leads to early acidic fluids enriched in Mg, Fe and other metals, consistent with signs of low-pH alteration in chondrites. Neutralization of these solutions leads to alkaline Na-rich fluids. Sulfate species have negligible concentrations in closed systems, which remain reduced, especially at elevated pressures created by forming H 2 gas. Hydrogen, CO 2, and H 2O dominate in the gaseous phase, though the abundance of methane cannot be fairly estimated.
KW - Asteroids, Composition
KW - Meteorites
KW - Mineralogy
KW - Prebiotic environments
KW - Satellites, Composition
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U2 - 10.1016/j.icarus.2012.05.036
DO - 10.1016/j.icarus.2012.05.036
M3 - Article
AN - SCOPUS:84863442639
SN - 0019-1035
VL - 220
SP - 713
EP - 729
JO - Icarus
JF - Icarus
IS - 2
ER -