Photon Factory Activity Report 2014 #32 (2015) B

BL-3A/2013G588

X-ray diffraction analysis of pristine micrometeorites recovered fromthe Antarctic surface snow
1Takuya Hirowatari*, Tomoki Nakamura, and Ken Tazawa
Department of Earth Sciences, Graduate School of Science, Tohoku University,Sendai, Miyagi 980-8576, Japan

1 Introduction
Micrometeorites (MMs) are extraterrestrial materials
that retain various information about the outer regions ofthe solar system. MMs recovered from the Antarctic
surface snow are characterized by a high content of Fesulfides and an unfractionated elemental abundancepatterns (CI norm.) of their fine-grained matrix, because
they experienced a lower degree of terrestrial alteration
than MMs from Antarctic blue ice field [1-2]. In order toinvestigate bulk mineralogy of individual MMs, we
performed synchrotron X-ray diffraction analysis on eachMM.
2 Samples and analytical techniques
The surface snow was collected near the Jangbogo
Antarctic Research Station by Korea Polar ResearchInstitute in 2014. We separated particles by melting andfiltering snow of ~400kg in a clean room. Several
thousands of lithic particles were picked up under thebinocular microscope and 126 particles were identified as
MMs based on SEM/EDS chemical analysis. After that,they were attached to the tops of carbon fibers 5μm indiameter. Individual MMs were analyzed for bulk
mineralogy by synchrotron-radiation X-ray diffraction
analysis at photon factory beamline 3A. The MMs wereset in a Gandolfi camera, and the average exposure timewas 45 minutes. The diffraction patterns were recorded in
an imaging plates, and the data were read by FLA7000
imaging plate reading system in order to analyze
diffraction patterns using a GANCON software.
3 Results and discussion
Synchrotron-radiation X-ray diffraction analysis foundthat the particle JBS14-0M-THP13D10 (Fig. 1a) has aunique mineralogy. Diffraction pattern of this particle(Fig. 2) indicates that this particle consists mainly of salt
minerals, halite (NaCl) and sylvite (KCl), which isinconsistent with the result of SEM/EDS analysis
revealing C-rich chondritic elemental abundance with Mg,
Si, Fe, and S being major elements of this particle (Fig.
1b). This incoherence suggests that these elements arecontained in amorphous material.
In the previous study, salt minerals were found in theordinary chondrites Zag and Monahans [3]. A recent
study suggests that the salt minerals in chondrites arederived from the primitive small bodies, such as C-, P-, orD-type asteroids being rich in organics and water [4]. The
results of this study could be strong evidence for thissuggestion. The salt minerals survived in this MM
because of short residence time in the snow.

abFig. 1: (a) Back-scattered electron image and (b) bulk
composition of JBS14-0M-THP13D10.

Fig. 2: A diffraction pattern of JBS14-0M-THP13D10.
Acknowledgement
We thank Drs. Nakao and Yamazaki for technicalsupport during X-ray diffraction analysis.
References[1]Duprat J. et al. (2007) Advances in Space Research 39,605-611. [2]Noguchi T. et al. (2006) Antarctic Meteorites
XXX, 87-88. [3]Zolensky M. E et al. (1999) Science 285,1377–1379. [4]Zolensky M. E et al. (2013) 76th Annual
Meeting of Meteoritical Society, abstract #5266.
* takuya.hirowatari.q3@dc.tohoku.ac.jp