TY - JOUR
T1 - Mineral associations and character of isotopically anomalous organic material in the Tagish Lake carbonaceous chondrite
AU - Zega, Thomas J.
AU - Alexander, Conel M.O.D.
AU - Busemann, Henner
AU - Nittler, Larry R.
AU - Hoppe, Peter
AU - Stroud, Rhonda M.
AU - Young, Andrea F.
N1 - Funding Information:
We thank Mike Zolensky for the samples of the Tagish Lake CC and Laurence Garvie for the reference samples of calcite, diamond, and graphite. We also thank them, Adrian Brearley, two anonymous referees, and AE Sandra Pizzarello for suggestions that improved the manuscript. We appreciate the assistance of Sue Wirick in setting up XANES experiments and Brad De Gregorio in processing XANES data. This research was supported by grants from the NASA Astrobiology, Cosmochemistry, and Origins of Solar Systems programs. A. Young was supported by a NSF Research Experience for Undergraduates Program at the Carnegie Institution.
PY - 2010/10
Y1 - 2010/10
N2 - 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.
AB - 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.
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U2 - 10.1016/j.gca.2010.07.018
DO - 10.1016/j.gca.2010.07.018
M3 - Article
AN - SCOPUS:84755161760
SN - 0016-7037
VL - 74
SP - 5966
EP - 5983
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 20
ER -