Presentation Information
[PPS12-P09]FIB-TOF-SIMS Analysis of Fine-Grained Chondrule Rims in the Allende CV3 Chondrite
*Shion Shirai1, Mamoru Masuda1, Tetsuo Sakamoto1,2 (1.Electrical Engineering and Electronics Program, Graduate School of Engineering, Kogakuin University, 2.Department of Applied Physics, School of Advanced Engineering, Kogakuin University)
Keywords:
Chondrule rims,Allende,CV3 chondrite,Matrix
Chondrules are the principal spherical silicate constituents of chondritic meteorites and are thought to have formed through high-temperature heating followed by rapid cooling in the primordial solar nebula. In carbonaceous chondrites, many chondrules are surrounded by rims composed of fine-grained minerals similar to the matrix. Chondrule rims are regarded as important records reflecting multiple formation processes, including dust accretion in the primordial solar nebula (Metzler et al., 1992) and subsequent alteration processes on the parent body (Tomeoka and Tanimura, 2000). These rims generally consist of fine-grained silicates, metallic iron, and sulfides, and their mineralogical compositions and textures provide key constraints on chondrite classification, thermal history, and fluid-rock interactions. Therefore, detailed mineralogical and chemical characterization of chondrule rims is essential for understanding post-chondrule dust accretion processes and secondary alteration histories on the parent body.
In this study, cross-sectional meteorite samples were prepared using a cross-section polisher (CP). Elemental distribution analyses were then conducted using a high-spatial-resolution Focused Ion Beam Time-of-Flight Secondary Ion Mass Spectrometer (FIB-TOF-SIMS) developed in our laboratory, targeting a continuous region from the chondrule interior through the fine-grained rim to the surrounding matrix in the Allende meteorite. Previous studies in our laboratory revealed the presence of nanoscale Al-rich particles predominantly located between olivine grains in the matrix (T.Sakamoto et al., 2022). Based on these prior findings, the objective of this study is to clarify the detailed elemental distribution within fine-grained chondrule rims and to discuss their formation processes.
The results show that particles similar to the nanoscale Al-rich grains previously identified in the matrix are also present within the fine-grained rims. In the matrix, these particles are mainly distributed between olivine grains, whereas in the fine-grained rims, pore spaces are reduced due to morphological modification of olivine grains, and Al-rich particles occur in a state apparently enclosed within olivine grains. These observations suggest that the fine-grained rims experienced a thermal history distinct from that of the surrounding matrix.
In this study, cross-sectional meteorite samples were prepared using a cross-section polisher (CP). Elemental distribution analyses were then conducted using a high-spatial-resolution Focused Ion Beam Time-of-Flight Secondary Ion Mass Spectrometer (FIB-TOF-SIMS) developed in our laboratory, targeting a continuous region from the chondrule interior through the fine-grained rim to the surrounding matrix in the Allende meteorite. Previous studies in our laboratory revealed the presence of nanoscale Al-rich particles predominantly located between olivine grains in the matrix (T.Sakamoto et al., 2022). Based on these prior findings, the objective of this study is to clarify the detailed elemental distribution within fine-grained chondrule rims and to discuss their formation processes.
The results show that particles similar to the nanoscale Al-rich grains previously identified in the matrix are also present within the fine-grained rims. In the matrix, these particles are mainly distributed between olivine grains, whereas in the fine-grained rims, pore spaces are reduced due to morphological modification of olivine grains, and Al-rich particles occur in a state apparently enclosed within olivine grains. These observations suggest that the fine-grained rims experienced a thermal history distinct from that of the surrounding matrix.