[P-PS06] Formation and evolution of planetary materials in the Solar System

[PPS06-10] Applications of infrared nano-spectroscopy for carbonaceous chondrites: To understand organic-mineral interactions during aqueous alteration

*Yoko Kebukawa¹, Norio Urayama², Hanae Kobayashi², Naoki Baden², Hans A. Bechtel³, Masashi Kondo⁴, Kensei Kobayashi¹ (1.Faculty of Engineering, Yokohama National University, 2.Nihon Thermal Consulting, 3.Advanced Light Source Division, Lawrence Berkeley National Laboratory, 4.Instrumental Analysis Center, Yokohama National University)

Keywords:Meteorites, Infrared spectroscopy

Organic matter in carbonaceous chondrites is distributed in fine grained matrix. Although 100 nm to <1 µm "nanoglobules" are often found in chondritic meteorites, these are ~10% of OM in chondrites [1], and the rest is smaller than nanoglobules. In order to understand pre- and post-accretion history of organic matter and its association with surrounding minerals, microscopic techniques are mandatory. Scanning transmission X-ray microscopy (STXM) combined with X-ray absorption near-edge structure (XANES) spectroscopy is so far the most suitable method in this purpose, that allows molecular structure information in ~40-nm spatial resolution. Infrared (IR) spectroscopy could be a complementary to XANES. However, the spatial resolution of IR is limited to a few micrometer, due to diffraction limit. Use of near-field light is one possibility to overcome the limitation of the spatial resolution. We have applied near-field IR spectroscopy to carbonaceous chondrites [2, 3]. However, the near-field signals are very low thus the intensity of IR light from a typical ceramic IR light source in a bench-top FTIR seems not large enough. Here, we applied two methods of high spatial resolution IR to carbonaceous chondrites, one is synchrotron infrared nanospectroscopy (SINS) using near-field IR with atomic force microscope (AFM) that is installed at Advances Light Source (ALS) beamline 5.4 [4, 5], other is AFM with its tip detecting thermal expansion of a sample resulting from absorption of infrared radiation (NanoIR2, Anasys Instruments) [e.g., 6].

We prepared ultramicrotomed thin sections of Murchison and Bells meteorites, as well as antigorite that was baked at 500 ^oC for 4 hours as a contamination control, since the IR absorption spectroscopy is susceptible to contamination from volatile organic matter [7]. We confirmed that both methods have at least 50-nm special resolutions. In the IR imaging, we observed that overlapping of regions that absorb 3400 cm⁻¹ corresponding to OH and 2920 cm⁻¹ corresponding to aliphatic CH, indicating association of organic matter with phyllosilicates. Such association is well known previously but in ~1 µm spatial resolutions [2, 3, 8]. We will further discuss parent body processes inferred from nano-scale IR imaging of Murchison and Bells meteorites.

References:
[1] Pizzarello S. et al., in Meteorites and the Early Solar System II, D.S. Lauretta and J.H.Y. McSween, Editors. 2006, University of Arizona Press: Tucson. p. 625-651.
[2] Kebukawa Y. et al. (2009) Chemistry Letters, 38, 22-23.
[3] Kebukawa Y. et al. (2010) Meteoritics & Planetary Science, 45, 394-405.
[4] Bechtel H. A. et al. (2014) Proceedings of the National Academy of Sciences, 111, 7191-7196.
[5] Dominguez G. et al. (2014) Nature Communications, 5.
[6] Dazzi A. and Prater C. B. (2017) Chemical Reviews, 117, 5146-5173.
[7] Kebukawa Y. et al. (2009) Meteoritics & Planetary Science, 44, 545-557.
[8] Yesiltas M. et al. (2015) Meteoritics & Planetary Science, 50, 1684-1696.