5:15 PM - 6:45 PM
[SCG51-P01] 3D morphology of CAIs and distribution of refractory elements: Perovskite recording the nebular gas condensation
Keywords:CAIs, 3D imaging of trace elements, Perovskite U–Pb dating, LA-ICP-MS
CAIs (calcium-aluminum-rich inclusions) are the oldest solids in the solar system, having formed near the proto-Sun through evaporation, condensation, and aggregation (and, in some cases, subsequent melting processes) at ~4,567.3 Ma (Connelly et al. 2012; Krot, 2019). While CAIs were suggested to have formed near the proto-Sun, their ubiquitous presence in chondrites, suggests that they experienced dynamical radial dissipation in the protoplanetary disk (Krot, 2019). Turbulent diffusion along the disk mid-plane (Ciesla, 2009) and X-wind and disk-wind above the disk surface (Bjerkeli et al., 2016) have been proposed as mechanisms for the dissipation. Although still under the debate for the mechanism, there is a recent attempt to constrain their mechanisms from the 2D geometry of CAIs (Lorenz et al., 2021). Therefore, the distribution of refractory elements in CAIs record the condensation and aggregation processes, and their shapes record the mass transport in the protoplanetary disk.
In this study, we developed a three-dimensional element imaging method (3D imaging) for CAIs and simultaneously acquires elemental distributions and shapes of CAIs to understand the condensation/aggregation and dissipation processes. The sample is CAIs from NWA 3118 which contains ultra-refractory inclusions (Zr, Sc, Y-minerals) (Xiong et al., 2020), and is considered to record the condensation, aggregation, and dissipation processes of the first stage of the protoplanetary disk. The sample was measured by LA-ICP-MS, which combines inductively coupled plasma mass spectrometry (ICP-MS) with a laser ablation (LA) method which is suitable for solid sample introduction, and we obtained images of 23 elements from Na to U. The size of CAIs was 1 mm square, and 2D imaging was obtained for 3 hours/1 image. 3D imaging was obtained by stacking them using in-house software (Suzuki et al., 2018).
From the distribution of the refractory elements in CAIs, we found that (i) perovskite is the carrier of U and Th in CAIs, (ii) U/Th in perovskite varies with size, and fine-grained perovskite condenses in the protoplanetary disk earlier, (iii) PGM elements are scattered as ~10 µm metal nuggets in the core of CAIs and are mechanically mixed with perovskite/silicates. Furthermore, the old perovskite U–Pb age of 4,575 Ma (2σ error: +18/-14 Ma) indicates that the timing of condensation of CAIs in previous studies reflect perovskite formation, and that the perovskite is a direct condensation product from the nebular gas. In this presentation, we will also present the 3D morphology of the CAIs and discuss the formation mechanism.
In this study, we developed a three-dimensional element imaging method (3D imaging) for CAIs and simultaneously acquires elemental distributions and shapes of CAIs to understand the condensation/aggregation and dissipation processes. The sample is CAIs from NWA 3118 which contains ultra-refractory inclusions (Zr, Sc, Y-minerals) (Xiong et al., 2020), and is considered to record the condensation, aggregation, and dissipation processes of the first stage of the protoplanetary disk. The sample was measured by LA-ICP-MS, which combines inductively coupled plasma mass spectrometry (ICP-MS) with a laser ablation (LA) method which is suitable for solid sample introduction, and we obtained images of 23 elements from Na to U. The size of CAIs was 1 mm square, and 2D imaging was obtained for 3 hours/1 image. 3D imaging was obtained by stacking them using in-house software (Suzuki et al., 2018).
From the distribution of the refractory elements in CAIs, we found that (i) perovskite is the carrier of U and Th in CAIs, (ii) U/Th in perovskite varies with size, and fine-grained perovskite condenses in the protoplanetary disk earlier, (iii) PGM elements are scattered as ~10 µm metal nuggets in the core of CAIs and are mechanically mixed with perovskite/silicates. Furthermore, the old perovskite U–Pb age of 4,575 Ma (2σ error: +18/-14 Ma) indicates that the timing of condensation of CAIs in previous studies reflect perovskite formation, and that the perovskite is a direct condensation product from the nebular gas. In this presentation, we will also present the 3D morphology of the CAIs and discuss the formation mechanism.