Mineral associations and character of isotopically anomalous organic material in the Tagish Lake carbonaceous chondrite

Thomas Zega, Conel M O D Alexander, Henner Busemann, Larry R. Nittler, Peter Hoppe, Rhonda M. Stroud, Andrea F. Young

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

We report a coordinated analytical study of matrix material in the Tagish Lake carbonaceous chondrite in which the same small (≤20 μm) fragments were measured by secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), electron energy-loss spectroscopy (EELS), and X-ray absorption near-edge spectroscopy (XANES). SIMS analysis reveals H and N isotopic anomalies (hotspots), ranging from hundreds to thousands of nanometers in size, which are present throughout the fragments. Although the differences in spatial resolution of the SIMS techniques we have used introduce some uncertainty into the exact location of the hotspots, in general, the H and N isotopic anomalies are spatially correlated with C enrichments, suggesting an organic carrier. TEM analysis, enabled by site-specific extraction using a focused-ion-beam scanning-electron microscope, shows that the hotspots contain an amorphous component, Fe-Ni sulfides, serpentine, and mixed-cation carbonates. TEM imaging reveals that the amorphous component occurs in solid and porous forms, EDS indicates that it contains abundant C, and EELS and XANES at the C K edge reveal that it is largely aromatic. This amorphous component is probably macromolecular C, likely the carrier of the isotopic anomalies, and similar to the material extracted from bulk samples as insoluble organic matter. However, given the large sizes of some of the hotspots, the disparity in spatial resolution among the various techniques employed in our study, and the phases with which they are associated, we cannot entirely rule out that some of the isotopic anomalies are carried by inorganic material, e.g., sheet silicates. The isotopic composition of the organic matter points to an initially primitive origin, quite possibly within cold interstellar clouds or the outer reaches of the solar protoplanetary disk. The association of organic material with secondary phases, e.g., serpentine and carbonates, suggests that the organic matter was susceptible to parent-body processing, and thus, isotopic dilution.

Original languageEnglish (US)
Pages (from-to)5966-5983
Number of pages18
JournalGeochimica et Cosmochimica Acta
Volume74
Issue number20
DOIs
StatePublished - Oct 2010
Externally publishedYes

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carbonaceous chondrite
Minerals
Lakes
Secondary ion mass spectrometry
spectroscopy
Biological materials
anomaly
transmission electron microscopy
ion
mass spectrometry
Electron energy loss spectroscopy
Carbonates
X ray absorption
lake
mineral
Transmission electron microscopy
organic matter
electron
Energy dispersive spectroscopy
spatial resolution

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Mineral associations and character of isotopically anomalous organic material in the Tagish Lake carbonaceous chondrite. / Zega, Thomas; Alexander, Conel M O D; Busemann, Henner; Nittler, Larry R.; Hoppe, Peter; Stroud, Rhonda M.; Young, Andrea F.

In: Geochimica et Cosmochimica Acta, Vol. 74, No. 20, 10.2010, p. 5966-5983.

Research output: Contribution to journalArticle

Zega, Thomas ; Alexander, Conel M O D ; Busemann, Henner ; Nittler, Larry R. ; Hoppe, Peter ; Stroud, Rhonda M. ; Young, Andrea F. / Mineral associations and character of isotopically anomalous organic material in the Tagish Lake carbonaceous chondrite. In: Geochimica et Cosmochimica Acta. 2010 ; Vol. 74, No. 20. pp. 5966-5983.
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