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Solar Wind Like Noble Gases in a Chondrule in the NWA 852 CR2 Chondrite

Introduction: Chondrules are free from trapped noble gases [e.g., 1], which is attributed to complete degassing during the chondrule formation. However, Okazaki et al. [2] discovered the Ar-rich trapped noble gases in enstatite chondrite chondrules. The Ar-rich gases were formed via incomplete degassing (He and Ne depletion) of implanted solar gases during the chondrule formation [2]. Since solar winds cannot penetrate the solar nebula [3], the chondrule precursors should have been located at the inner edge of the solar nebula to acquire the solar gases, suggesting the chon-drule formation near the Sun [2]. Thus, noble gases would have a clue for the formation location of the chondrules, although chondrules are the high temperature products. We found through laser extraction noble gas analysis of the NWA 852 CR2 chondrite [4] that a chon-drule contains solar wind like noble gases in its interior. Here we focus this result and discuss possible acquisition process of the solar wind like noble gases. Laser extraction noble gas analysis: A polished thick section (~ 300 µm thick) of NWA 852 was prepared for SEM observation followed by noble gas analysis. Noble gases were extracted with a Nd-YAG laser (~ 30 µm in diameter). For one measurement of the individual sites of the chondrule, twenty five pits were made (fused mass is approximately 16 µg by assuming ρ is ~ 3 g/cm 3). Extracted noble gases were analyzed with a noble gas mass spectrometer (MS-III) at University of Tokyo. Three-dimensional image of the analyzed chon-drule was obtained using synchrotron radiation X-ray CT at BL20B2 of SPring-8, with X-ray energy of 27 keV and pixel size 2.74 µm. Laser pits and internal texture of the chondrule were observed. Noble gas data, of which laser pits grazed matrix, were excluded (not surrounded by dashed lines in Fig. 1), because matrix contains high concentrations of solar noble gases [4]. Results: The chondrule shows porphyritic texture and consists of Mg-rich olivine, low-Ca pyroxene, and Ca-plagioclase, suggestive of a type IAB chondrule. Helium and neon isotopic ratios of the most sites of the chondrule are explained by cosmogenic component and radiogenic 4 He (Fig. 1). The inner sites of the chondrule appear to show a solar contribution.