Abstract
AbstractWe present in this study the effects of short‐term heating on organics in the Tagish Lake meteorite and how the difference in the heating conditions can modify the organic matter (OM) in a way that complicates the interpretation of a parent body's heating extent with common cosmothermometers. The kinetics of short‐term heating and its influence on the organic structure are not well understood, and any study of OM is further complicated by the complex alteration processes of the thermally metamorphosed carbonaceous chondrites—potential analogues of the target asteroid Ryugu of the Hayabusa2 mission—which had experienced posthydration, short‐duration local heating. In an attempt to understand the effects of short‐term heating on chondritic OM, we investigated the change in the OM contents of the experimentally heated Tagish Lake meteorite samples using Raman spectroscopy, scanning transmission X‐ray microscopy utilizing X‐ray absorption near edge structure spectroscopy, and ultraperformance liquid chromatography fluorescence detection and quadrupole time of flight hybrid mass spectrometry. Our experiment suggests that graphitization of OM did not take place despite the samples being heated to 900 °C for 96 h, as the OM maturity trend was influenced by the heating conditions, kinetics, and the nature of the OM precursor, such as the presence of abundant oxygenated moieties. Although both the intensity of the 1s−σ* exciton cannot be used to accurately interpret the peak metamorphic temperature of the experimentally heated Tagish Lake sample, the Raman graphite band widths of the heated products significantly differ from that of chondritic OM modified by long‐term internal heating.
Highlights
Carbonaceous chondrites exhibit a wide range of aqueous and thermal alteration characteristics, while some are known to demonstrate mineralogical and petrologic evidence of having been thermally metamorphosed after aqueous alteration
While phyllosilicates, magnetite, and Fe-Ni sulfides are common mineral phases observed in the matrix of the unheated carbonate-poor lithology of the Tagish Lake meteorite (Zolensky et al 2002), the Tagish Lake samples heated to 900 °C show mineral assemblages of predominantly anhydrous silicates, metal, and troilite, implying a reducing heating environment
We explore the effects of short-term heating on the organic matter (OM) in the carbonate-poor, aqueously altered lithology of the Tagish Lake meteorite with Raman spectroscopy, C-X-ray absorption near edge structure (XANES), and UPLC-FD/QToF-MS
Summary
Carbonaceous chondrites exhibit a wide range of aqueous and thermal alteration characteristics, while some are known to demonstrate mineralogical and petrologic evidence of having been thermally metamorphosed after aqueous alteration Their occurrences challenge the initial view of which carbonaceous chondrites, that have experienced pervasive aqueous alteration, were not extensively heated. This group of dehydrated meteorites are commonly referred to as thermally metamorphosed carbonaceous chondrites (TMCCs), and their relatively flat visible near-infrared reflectance spectra resemble that of C-, G-, B-, and F-type asteroids that typically have low albedos (Gaffey et al 1989; Hiroi et al 1993, 1996). The heating conditions of TMCCs were estimated to be 10 to 103 days at 700 °C to 1 to 100 h at 890 °C, which suggest that they have experienced short-term heating possibly induced by impact and/or solar radiation (Nakato et al 2008; Yabuta et al 2010; Chan et al 2017b)
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