^1,2Yoko Kebukawa,³Michael E. Zolensky,⁴A. L. David Kilcoyne,⁵Zia Rahman,^6,7Peter Jenniskens,¹George D. Cody
¹Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, USA
²Department of Natural History Sciences, Hokkaido University, Sapporo, Japan
³NASA Johnson Space Center, Houston, Texas, USA
⁴Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, USA
⁵Jacobs-Sverdrup, Houston, Texas, USA
⁶SETI Institute, Mountain View, California, USA
⁷NASA Ames Research Center, Moffett Field, California, USA

The Sutter’s Mill (SM) meteorite fell in El Dorado County, California, on April 22, 2012. This meteorite is a regolith breccia composed of CM chondrite material and at least one xenolithic phase: oldhamite. The meteorite studied here, SM2 (subsample 5), was one of three meteorites collected before it rained extensively on the debris site, thus preserving the original asteroid regolith mineralogy. Two relatively large (10 μm sized) possible diamond grains were observed in SM2-5 surrounded by fine-grained matrix. In the present work, we analyzed a focused ion beam (FIB) milled thin section that transected a region containing these two potential diamond grains as well as the surrounding fine-grained matrix employing carbon and nitrogen X-ray absorption near-edge structure (C-XANES and N-XANES) spectroscopy using a scanning transmission X-ray microscope (STXM) (Beamline 5.3.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory). The STXM analysis revealed that the matrix of SM2-5 contains C-rich grains, possibly organic nanoglobules. A single carbonate grain was also detected. The C-XANES spectrum of the matrix is similar to that of insoluble organic matter (IOM) found in other CM chondrites. However, no significant nitrogen-bearing functional groups were observed with N-XANES. One of the possible diamond grains contains a Ca-bearing inclusion that is not carbonate. C-XANES features of the diamond-edges suggest that the diamond might have formed by the CVD process, or in a high-temperature and -pressure environment in the interior of a much larger parent body.

Reference
Kebukawa Y, Zolensky ME, Kilcoyne ALD, Rahman Z, Jenniskens P, Cody GD (2014) Diamond xenolith and matrix organic matter in the Sutter’s Mill meteorite measured by C-XANES. Meteoritics&Planetary Science (in Press)
Linke to Article [DOI: 10.1111/maps.12312]

Published in agreement with John Wiley&Sons

¹Yamakawa, A. ¹Yin, Q.-Z.
¹Department of Earth and Planetary Sciences, University of California at Davis, Davis, California, USA

Recent studies have shown that major meteorite groups possess their own characteristic 54Cr values, demonstrating the utility of Cr isotopes for identifying genetic relationships between the planetary materials in conjunction with other classical tools, such as oxygen isotopes. In this study, we performed Cr isotope analyses for whole rocks and chemically separated phases of the new CM2 chondrite, Sutter’s Mill (SM 43 and 51). The two whole rocks of Sutter’s Mill show essentially identical ε54Cr excesses (SM 43 = +0.95 ± 0.09ε, SM 51 = +0.88 ± 0.07ε), relative to the Earth. These values are the same within error with that of the CM2-type Murchison (+0.89 ± 0.08ε), suggesting that parent bodies of Sutter’s Mill and Murchison were formed from the same precursor materials in the solar nebula. Large ε54Cr excess of up to 29.40ε is observed in the silicate phase of Sutter’s Mill, while that of Murchison shows 15.74ε. Importantly, the leachate fractions of both Sutter’s Mill and Murchison form a steep linear anticorrelation between ε54Cr and ε53Cr, cross-cutting the positive correlation previously observed in carbonaceous chondrites. The fact that L4 acid leachate fraction contains higher 54Cr excesses than that of L5 step designed to dissolve refractory minerals suggests that spinel is not a major 54Cr carrier. We also note that L5 contains 53Cr anomalies lower than the solar initial value, suggesting it carries a component of nucleosynthetic anomaly unrelated to the 53Mn decay. We have identified five endmember components of nucleosynthetic origin among the early solar system materials.

Reference
Yamakawa A, Yin Q-Z (2014) Chromium isotopic systematics of the Sutter’s Mill carbonaceous chondrite: Implications for isotopic heterogeneities of the early solar system. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12346]

Published by arrangement with John Wiley&Sons

¹Yesiltas, M., ²Kebukawa, Y., ¹Peale, R. E., ³Mattson, E., ³Hirschmugl, C. J., ^4,5Jenniskens, P.
¹Department of Physics, University of Central Florida, Orlando, Florida, USA
²Faculty of Engineering, Yokohama National University, Hodogaya-ku, Yokohama, Japan
³Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA
⁴SETI Institute, Mountain View, California, USA
⁵NASA Ames Research Center, Moffett Field, California, USA

Synchrotron-based Fourier transform infrared spectroscopy and Raman spectroscopy are applied with submicrometer spatial resolution to multiple grains of Sutter’s Mill meteorite, a regolith breccia with CM1 and CM2 lithologies. The Raman and infrared active functional groups reveal the nature and distribution of organic and mineral components and confirm that SM12 reached higher metamorphism temperatures than SM2. The spatial distributions of carbonates and organic matter are negatively correlated. The spatial distributions of aliphatic organic matter and OH relative to the distributions of silicates in SM2 differ from those in SM12, supporting a hypothesis that the parent body of Sutter’s Mill is a combination of multiple bodies with different origins. The high aliphatic CH2/CH3 ratios determined from band intensities for SM2 and SM12 grains are similar to those of IDPs and less altered carbonaceous chondrites, and they are significantly higher than those in other CM chondrites and diffuse ISM objects.

Reference
Yesiltas M, Kebukawa Y, Peale RE, Mattson E, Hirschmugl CJ, Jenniskens P (2014) Infrared imaging spectroscopy with micron resolution of Sutter’s Mill meteorite grains. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12321]

Published by arangement with John Wiley&Sons