Reaction of Q to thermal metamorphism in parent bodies: Experimental simulation

Abstract

Planetary noble gases in chondrites are concentrated in an unidentified carrier phase, called “Q.” Phase Q oxidized at relatively low temperature in pure oxygen is a very minor part of insoluble organic matter (IOM), but has not been separated in a pure form. High‐pressure (HP) experiments have been used to test the effects of thermal metamorphism on IOM from the Orgueil (CI1) meteorite, at conditions up to 10 GPa and 700 °C. The effect of the treatment on carbon structural order was characterized by Raman spectroscopy of the carbon D and G bands. The Raman results show that the IOM becomes progressively more graphite‐like with increasing intensity and duration of the HP treatment. The carbon structural transformations are accompanied by an increase in the release temperatures for IOM carbon and 36Ar during stepped combustion (the former to a greater extent than the latter for the most HP treated sample) when compared with the original untreated Orgueil (CI1) sample. The 36Ar/C ratio also appears to vary in response to HP treatment. Since 36Ar is a part of Q, its release temperature corresponds to that for Q oxidation. Thus, the structural transformations of Q and IOM upon HP treatment are not equal. These results correspond to observations of thermal metamorphism in the meteorite parent bodies, in particular those of type 4 enstatite chondrites, e.g., Indarch (EH4), where graphitized IOM oxidized at significantly higher temperatures than Q (Verchovsky et al. ). Our findings imply that Q is less graphitized than most of the macromolecular carbonaceous material present during parent body metamorphism and is thus a carbonaceous phase distinct from other meteoritic IOM.

A confocal-controlled Raman-LIBS hybrid microscope with high stability and spatial resolution

“…46 Verchovsky and coworkers have shown that Γ D increases with thermal alteration, where a larger D-to-G intensity ratio I D / I G suggests a reduction of the thermal alteration. 46…”

“…46–49 The D-band width ( Γ D ) has been reported to be more sensitive to thermal metamorphism than the G-band width ( Γ G ) and is considered a more accurate probe for the thermal history of the parent asteroid. 46 Verchovsky and coworkers have shown that Γ D increases with thermal alteration, where a larger D-to-G intensity ratio I D / I G suggests a reduction of the thermal alteration. 46…”

“…46 Verchovsky and coworkers have shown that G D increases with thermal alteration, where a larger D-to-G intensity ratio I D /I G suggests a reduction of the thermal alteration. 46 To analyze the thermal history, we extracted at least 100 Raman spectra from carbon-rich sites in each region in NWA13323 and tted these spectra to the Lorentzian function to obtain carbon peak widths and intensities. Inside the spherulites, the dark blue regions of the image consist mainly of olivine and pyroxene with weak carbon D and G peaks, as this may lead to inaccurate estimations of the meteorite's thermal history, we excluded these points in all the analyses described in this section.…”

“…Thermal metamorphism modies the structural order of the carbonaceous matter in meteorites and thus can be reected in the D-band and G-band spectral parameters. [46][47][48][49] The D-band width (G D ) has been reported to be more sensitive to thermal metamorphism than the G-band width (G G ) and is considered a more accurate probe for the thermal history of the parent asteroid. 46 Verchovsky and coworkers have shown that G D increases with thermal alteration, where a larger D-to-G intensity ratio I D /I G suggests a reduction of the thermal alteration.…”

“…[46][47][48][49] The D-band width (G D ) has been reported to be more sensitive to thermal metamorphism than the G-band width (G G ) and is considered a more accurate probe for the thermal history of the parent asteroid. 46 Verchovsky and coworkers have shown that G D increases with thermal alteration, where a larger D-to-G intensity ratio I D /I G suggests a reduction of the thermal alteration. 46 To analyze the thermal history, we extracted at least 100 Raman spectra from carbon-rich sites in each region in NWA13323 and tted these spectra to the Lorentzian function to obtain carbon peak widths and intensities.…”