11:00 AM - 11:15 AM
[PPS08-08] Effect of the organic mineral formed by aqueous alteration of Allende meteorite on Mg/Fe fractionation
Keywords:oranic mineral, aqueous alteration, Mg/Fe fractination, snow lines of the solar system
Carbonaceous chondrites are important for understanding the origin and evolution of the solar system. Many experiments on aqueous alteration from meteoritic materials have been carried out using the carbonaceous chondrite, the Allende meteorite (e.g., Jones and Brearley, 2006). The main purpose of these experiments is to reproduce highly altered carbonaceous meteorites, such as CI chondrites, with fluids that are free of organic compounds. However, in planetesimals formed outside snow lines of the primordial solar system, fluids may contain organic compounds derived from accumulated solid particles with C/O ratios determined by the snow lines for each chemical species. In the early stages of planetary evolution, meteoritic material was interacted with fluids characteristic of distance from the Sun.
In this study, we focused on objects between 2-10 AU and 10-40 AU based on Oberg et al. (2011) and estimated fluid composition from the snow lines of molecules, including C and O, in the primordial solar system disk. We carried out experiments on the interaction between fluids and meteoritic material under hydrothermal conditions. The C/O ratio of fluid was reproduced using HCOOH (formic acid), C2H5OH (ethanol), and H2O. Organic acids and hydrocarbons (such as ethyl formate) have been reported to be ubiquitous wherever planetary system formation (Yang et al., 2021). The fluid compositions were a solution of ~16 wt% formic acid and ~10 wt% ethanol (fluid a) and a solution of ~30 wt% formic acid and ~19 wt% ethanol (fluid b). The solid phase was powdered Allende meteorite, a nonequilibrium carbonaceous chondrite that had not undergone aqueous alteration. The solid/liquid ratio was 1:1 by weight. The experiments were carried out at a temperature of 150°C for 10 days, 40 days, and 120 days. The pressure was the saturated vapor pressure.
Experimental products were analyzed by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). XRD analysis showed dashkovaite (Mg(HCOO)2•2(H2O)) peaks at 10 days with solution a and at 10, 40, and 120 days with solution b (Fig. 1). This organic mineral was also confirmed by SEM observation. Fig. 2 shows SEM images of dashkovaite observed in each run of solution b. Fig. 3 shows the molar ratios of Mg, Fe, and Si in the alteration product determined by EDS analysis. Table 1 shows the number of measurement points, the average and standard deviation of the Mg/(Mg+Fe)×100 ratio (Mg#) for the alteration product except dashkovaite, and the number of measurement points for dashkovaite and Mg# showed in Fig. 3
In the initial stage of reaction, Fe-bearing dashkovaite with Mg# ~70 grew rapidly from the solution, and then Mg# increased to ~ 90. Dashkovaite released Fe into the surrounding alteration product through aqueous alteration. As a result, Mg# in silicious alteration products became richer in Fe than Mg# in the solar abundance. The silicious alteration products may be a precursor of Fe-rich phyllosilicate that occurred in highly altered carbonaceous chondrites.
Reference
Oberg K. I., Murray-Clay R., and Bergin E. A. (2011) Astrophysical Journal Letters, 743, L16(5pp).
Jones C. L. and Brealey A. J. (2006) Geochimica Cosmochimica Acta, 70(4), 1040-1058.
Yang Y. et al. (2021) The Astrophysical Journal, 91020(38pp).
In this study, we focused on objects between 2-10 AU and 10-40 AU based on Oberg et al. (2011) and estimated fluid composition from the snow lines of molecules, including C and O, in the primordial solar system disk. We carried out experiments on the interaction between fluids and meteoritic material under hydrothermal conditions. The C/O ratio of fluid was reproduced using HCOOH (formic acid), C2H5OH (ethanol), and H2O. Organic acids and hydrocarbons (such as ethyl formate) have been reported to be ubiquitous wherever planetary system formation (Yang et al., 2021). The fluid compositions were a solution of ~16 wt% formic acid and ~10 wt% ethanol (fluid a) and a solution of ~30 wt% formic acid and ~19 wt% ethanol (fluid b). The solid phase was powdered Allende meteorite, a nonequilibrium carbonaceous chondrite that had not undergone aqueous alteration. The solid/liquid ratio was 1:1 by weight. The experiments were carried out at a temperature of 150°C for 10 days, 40 days, and 120 days. The pressure was the saturated vapor pressure.
Experimental products were analyzed by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). XRD analysis showed dashkovaite (Mg(HCOO)2•2(H2O)) peaks at 10 days with solution a and at 10, 40, and 120 days with solution b (Fig. 1). This organic mineral was also confirmed by SEM observation. Fig. 2 shows SEM images of dashkovaite observed in each run of solution b. Fig. 3 shows the molar ratios of Mg, Fe, and Si in the alteration product determined by EDS analysis. Table 1 shows the number of measurement points, the average and standard deviation of the Mg/(Mg+Fe)×100 ratio (Mg#) for the alteration product except dashkovaite, and the number of measurement points for dashkovaite and Mg# showed in Fig. 3
In the initial stage of reaction, Fe-bearing dashkovaite with Mg# ~70 grew rapidly from the solution, and then Mg# increased to ~ 90. Dashkovaite released Fe into the surrounding alteration product through aqueous alteration. As a result, Mg# in silicious alteration products became richer in Fe than Mg# in the solar abundance. The silicious alteration products may be a precursor of Fe-rich phyllosilicate that occurred in highly altered carbonaceous chondrites.
Reference
Oberg K. I., Murray-Clay R., and Bergin E. A. (2011) Astrophysical Journal Letters, 743, L16(5pp).
Jones C. L. and Brealey A. J. (2006) Geochimica Cosmochimica Acta, 70(4), 1040-1058.
Yang Y. et al. (2021) The Astrophysical Journal, 91020(38pp).