5:15 PM - 6:45 PM
[PPS08-P08] Heating experiments of carbonaceous chondrites using a sapphire anvil cell.
Keywords:carbonaceous chondrites, heating experiments, Raman spectroscopy
Introduction
Carbonaceous chondrites are formed in the solar nebula and have undergone varying degrees of secondary aqueous alteration and thermal metamorphism. Many primitive carbonaceous chondrites exhibit heterogeneity in the degree of thermal metamorphism [e.g.,1], indicating that these asteroids underwent local heating processes that differed from large-scale thermal metamorphism. To better understand the thermal evolution of carbonaceous asteroids, we performed in-situ Raman measurements on carbonaceous chondrites through heating experiments at relatively low temperatures, and examined the changes in the carbon structure of organic matter.
Methods
Two carbonaceous chondrites Allende (type 3 CV) and Jbilet Winselwan (type 2 CM) are examined by AIRIX STR-RD-110D Raman spectrometer equipped with a heating stage at Saitama University. Type 3 and type 2 chondrites differ in their degree of aqueous alteration and the amount of carbon they contain; type 2 chondrites typically contain 0.8-2.8% carbon, while type 3 chondrites contain 0.2-1 wt% carbon [2].
The small grains of carbonaceous chondrites Allende and Jbilet Winselwan were placed in the sapphire anvil cell, and Raman spectra were collected at every 50oC with increasing the temperature under the atmospheric pressure. Although heating experiments on carbonaceous chondrites have been performed in previous studies [e.g., 3], this method has the advantage of allowing the Raman analysis with temperature changes of the same single grain. The peak positions of D (defect) and G (graphite) bands of polyaromatic organic matter and their peak widths (Full width half maximum, FWHM) were obtained for each spectrum using fitting profiles of Lorentzian for D band, and Breit-Wigner-Fano for G band, respectively.
Results and Discussion
The grains of Allende and Jbilet Winselwan placed were examined for the changes in heating from room temperature to 300 °C and 250 °C, respectively. In both samples, water vapor is observed around ~100°C to 200 °C, released from the sample and the glue holding the anvil cell. No obvious optical changes were observed in Allende grains under 300 °C. However, the Jbilet Winselwan grains reacted with the water to form a black and sticky alteration product when heated above 250°C. Chemical analysis was not possible due to the small amount of the alteration product.
Previous studies on carbonaceous chondrites have shown that the D bandwidth decreases, and the intensity ratio ID/IG increases with thermal maturity of the organic matter [4,5]. We observe no systematic trend in Raman parameters of Allende with increasing the temperature under 250oC. Jbilet Winselwan samples exhibit a large variation in FWHMD and ID/IG, with no clear trend observed with temperature. Although no systematic changes in the Raman parameters of both samples were observed within the studied temperature range (below 250°C), heating Jubilet Winseltwan above 150°C resulted in an increase in fluorescence background and alteration of the sample. This indicates that the amount of organic matter present in the sample may affect the Raman spectral changes caused by heating.
References: [1] Nakamura (2005) Journal of Mineralogical and Petrological Sciences, 100: 260-272. [2] Weisberg et al. (2006) Meteorites and the Early Solar System II, 19-52. [3] Chan et al. (2019) Meteoritics & Planet. Sci., 54: 104-125. [4] Bonal et al. (2006) Geochim Cosmochism Acta, 70: 1849-1863. [5] Bonal et al. (2024) Icarus, 408: Article 115826.
Carbonaceous chondrites are formed in the solar nebula and have undergone varying degrees of secondary aqueous alteration and thermal metamorphism. Many primitive carbonaceous chondrites exhibit heterogeneity in the degree of thermal metamorphism [e.g.,1], indicating that these asteroids underwent local heating processes that differed from large-scale thermal metamorphism. To better understand the thermal evolution of carbonaceous asteroids, we performed in-situ Raman measurements on carbonaceous chondrites through heating experiments at relatively low temperatures, and examined the changes in the carbon structure of organic matter.
Methods
Two carbonaceous chondrites Allende (type 3 CV) and Jbilet Winselwan (type 2 CM) are examined by AIRIX STR-RD-110D Raman spectrometer equipped with a heating stage at Saitama University. Type 3 and type 2 chondrites differ in their degree of aqueous alteration and the amount of carbon they contain; type 2 chondrites typically contain 0.8-2.8% carbon, while type 3 chondrites contain 0.2-1 wt% carbon [2].
The small grains of carbonaceous chondrites Allende and Jbilet Winselwan were placed in the sapphire anvil cell, and Raman spectra were collected at every 50oC with increasing the temperature under the atmospheric pressure. Although heating experiments on carbonaceous chondrites have been performed in previous studies [e.g., 3], this method has the advantage of allowing the Raman analysis with temperature changes of the same single grain. The peak positions of D (defect) and G (graphite) bands of polyaromatic organic matter and their peak widths (Full width half maximum, FWHM) were obtained for each spectrum using fitting profiles of Lorentzian for D band, and Breit-Wigner-Fano for G band, respectively.
Results and Discussion
The grains of Allende and Jbilet Winselwan placed were examined for the changes in heating from room temperature to 300 °C and 250 °C, respectively. In both samples, water vapor is observed around ~100°C to 200 °C, released from the sample and the glue holding the anvil cell. No obvious optical changes were observed in Allende grains under 300 °C. However, the Jbilet Winselwan grains reacted with the water to form a black and sticky alteration product when heated above 250°C. Chemical analysis was not possible due to the small amount of the alteration product.
Previous studies on carbonaceous chondrites have shown that the D bandwidth decreases, and the intensity ratio ID/IG increases with thermal maturity of the organic matter [4,5]. We observe no systematic trend in Raman parameters of Allende with increasing the temperature under 250oC. Jbilet Winselwan samples exhibit a large variation in FWHMD and ID/IG, with no clear trend observed with temperature. Although no systematic changes in the Raman parameters of both samples were observed within the studied temperature range (below 250°C), heating Jubilet Winseltwan above 150°C resulted in an increase in fluorescence background and alteration of the sample. This indicates that the amount of organic matter present in the sample may affect the Raman spectral changes caused by heating.
References: [1] Nakamura (2005) Journal of Mineralogical and Petrological Sciences, 100: 260-272. [2] Weisberg et al. (2006) Meteorites and the Early Solar System II, 19-52. [3] Chan et al. (2019) Meteoritics & Planet. Sci., 54: 104-125. [4] Bonal et al. (2006) Geochim Cosmochism Acta, 70: 1849-1863. [5] Bonal et al. (2024) Icarus, 408: Article 115826.