Photon Factory Activity Report 2014 #32 (2015) B

BL-13A/2013S2-003

Investigation of Organic Matter in the Matrix of Allende Meteorite byCompact Scanning Transmission X-ray Microscopy
Hiroki Suga1,*, Yasuo Takeichi2, Chihiro Miyamoto3, Kazuhiko Mase2,
Kanta Ono2, and Yoshio Takahashi1-3
1Department of Earth and Planetary Systems Science, Graduate School of Science,
Hiroshima University, Hiroshima 739-8526, Japan
2
Institute of Materials Structure Science, High-Energy Accelerator Research Organization (KEK),Oho, Tsukuba, Ibaraki 305-0801, Japan3
Department of Earth and Planetary Science, Graduate School of Science,
The University of Tokyo, Tokyo 113-0033, Japan
1 Introduction
Allende meteorite (Allende), which is classed ascarbonaceous meteorite (CV3), fell in Pueblito deAllende, Chihuahua State, Mexico, on February 8, 1969.
Allende is composed of chondrule, calcium-aluminiumrich inclusions (CAIs), amoeboid olivine aggregates(AOAs), Fe/Ni metal, and matrix. Organic matter (OM) is
contained in matrix phase. Distribution of OM in thematrix of Allende at the submicron-scale, however, has
not investigated yet.
2 Experiment
In this study, we investigated a focused ion beam (FIB)
milled thin section (approximately 150 nm) of Allendetransected a region of fine-grained matrix employing
carbon X-ray absorption near-edge structure (C-XANES)
spectroscopy using compact scanning transmission X-ray
microscope (compact STXM), which is installed to BL13A at Photon Factory, high energy acceleration researchorganization. The specimen is shown in Figure 1.

Fig. 1: SEM secondary electron image of the thin foil
specimen for compact STXM.
3 Results and Discussion
The compact STXM analysis revealed that the thinsection of matrix of Allende contains C-rich grains anddiffuse OM (Figure 2). The C-XANES spectra wereobtained from seven of C-rich grains, which are similar to
Allende’s insoluble organic matter (IOM) reported byCody et al. (2008).
Some of seven C-rich grains has

exciton peak of the diamond (288.6-288.9 eV). Existenceof this peak indicates the possibility that nano-diamonds
are contained in these grains. In addition, one of the Crich grains has possibility of contain of C-N bond (nitrileor heterocyclic imine).	

Fig. 2: Carbon elemental image of the specimen.
As to diffuse OM, distributing like vein, whose CXANES were carboxylic rich OM compared to grains.
Diffuse OM was investigated in CM and CI chondrites byC-XANES, whose compositions were mainly labile- andlow-molecules OM and which was carboxylic rich OM
was reported by Le Guillou et al. (2014). However, CXANES of diffuse OM, was investigated in this study, isdifferent from that reported previously. This difference
caused from the difference of empirical temperature
between CV, CI, and CM.
From these results, OM is existed in matrix phase assmall grain and diffuse OM. And compact STXM
measurement was revealed that speciation of OM. Grains
have IOM-like feature, and possibility of containing
nano-diamonds and C-N compounds. Diffuse OM iscarboxylic-rich OM.
As to the future work, existence of nano-diamonds andC-N compounds should be confirmed by TEM
observation and N-XANES, respectively. In addition,metamorphosis between OM and inorganic minerals
when thermal denaturation should be investigated bycompact STXM and Raman microscopy.
* hiro-suga@hiroshima-u.ac.jp