10:45 〜 12:15
[PPS08-P10] Further evidence for dust transport in the Solar protoplanetary disk inferred from oxygen isotope analyses of DOM 08006 (CO3.01) chondrules
キーワード：原始太陽系円盤、コンドルール、酸素同位体、物質輸送
Further evidence for dust transport in the Solar protoplanetary disk inferred from oxygen isotope analyses of chondrules in the DOM 08006 (CO3.01) carbonaceous chondrite
Kohei Fukuda, Mingming Zhang, Travis Tenner, Makoto Kimura, Noriko Kita
Chondrules from different chondrite groups have distinct characteristics including oxygen isotopes, indicating that asteroid accretion was localized in respective regions of the protoplanetary disk [e.g., 1]. The majority of chondrules in non-carbonaceous chondrites (NCs) exhibit positive Δ17O values (0 to 3 ‰; Δ17O = δ17O − 0.52 ×δ18O), which are systematically higher than those in carbonaceous chondrites (CCs: Δ17O from −6 to 0 ‰) [2]. By considering the isotopic dichotomy in non-carbonaceous and carbonaceous groups [e.g., 3], including oxygen isotope ratios of their constituent chondrules, it is hypothesized chondrules in NC and CCs formed in distinct regions of the protoplanetary disk and subsequently accreted to respective parent asteroids [4, 5]. In contrast, combined O-Cr-Ti isotope studies of chondrules revealed the presence of mm sized chondrule populations with NC-like isotope signatures in CCs, indicating that some fraction of inner Solar System materials (i.e. NC chondrules) was transported outward and into CC chondrule-forming regions [4, 6]. The outward transport of mm sized dust is not consistent with the current understanding of isolated inner and outer Solar System reservoirs, which is inferred based on the isotopic dichotomy of bulk meteorite data [3]. To further investigate potential inner-to-outward disk transport signatures of materials, we conducted oxygen isotope analyses of chondrules in the DOM 08006 CO3.01 carbonaceous chondrite.
Thirty-two chondrules were selected for major element characterization via electron microprobe analysis, as well as oxygen isotope characterization using the WiscSIMS IMS 1280 secondary ion mass spectrometer at the University of Wisconsin-Madison. For SIMS, olivine and pyroxene grains were analyzed in a single session with a 2nA Cs primary ion beam (12 µm in diameter). Plagioclase grains were analyzed in another session with a 20 pA primary ion beam (3µm in diameter). Analytical conditions for both sessions are similar to those described in [7] and [8], respectively.
The DOM 08006 chondrules studied include 20 type I (Mg# > 90, where Mg# = [Mg]/[Mg+Fe] molar %) and 12 type II chondrules (Mg# < 90). The Δ17O values of type I chondrules with Mg# > 98 (N = 10) range from −6 to −4‰ [9]. Most of the other type I (N = 7) and type II (N = 10) chondrules have Δ17O values ranging from −3 to −2‰, which are systematically higher than those in type I chondrules with Mg > 98. The observed Δ17O-Mg# systematics in the DOM 08006 chondrules are similar to those in other pristine carbonaceous chondrites such as CV, CO, and CMs [e.g., 2, 10]. In addition to the universal Δ17O-Mg# trend among the majority of CC chondrules, we also found a distinct population (N = 5) with Δ17O values higher than 0‰, which is not common in the CV, CO, and CMs, but is more consistent with O-isotope signatures of metal-rich CC (CR, CB, CH) or NC chondrules [2]. Among the five 16O-poor chondrules, one chondrule exhibits MnO concentrations and Mg#s of olivine grains that are consistent with those of L3/LL3 type II chondrules, but not those of CR type II chondrules. This suggests that a minor population of chondrules in DOM 08006 either (1) initially formed in a NC reservoir and were then subsequently transported outward to where the parent body of DOM 08006 accreted; or (2) were transported from other CC chondrule-forming regions that produced chondrules with similar MnO-Mg# relationships, such as CH and CB chondrites.
[1] Jones (2012) MAPS 47, 1176-1190. [2] Tenner et al. (2018) In Chondrules, Records of Protoplanetary Disk Processes, 196-246. [3] Kruijer et al. (2020) NatAstron 4, 32-40. [4] Williams et al. (2020) PNAS 117, 23426-23435. [5] Schneider et al. (2020) EPSL 551, 116585. [6] Tenner et al. (2017) MAPS 52, 268-294. [7] Siron et al. (2021) GCA 293, 103-126. [8] Ushikubo et al. (2012) GCA 90, 242-264. [9] Kita et al. (2022) Goldschmidt conference, 10633. [10] Chaumard et al. (2021) GCA 299, 199-218.
Kohei Fukuda, Mingming Zhang, Travis Tenner, Makoto Kimura, Noriko Kita
Chondrules from different chondrite groups have distinct characteristics including oxygen isotopes, indicating that asteroid accretion was localized in respective regions of the protoplanetary disk [e.g., 1]. The majority of chondrules in non-carbonaceous chondrites (NCs) exhibit positive Δ17O values (0 to 3 ‰; Δ17O = δ17O − 0.52 ×δ18O), which are systematically higher than those in carbonaceous chondrites (CCs: Δ17O from −6 to 0 ‰) [2]. By considering the isotopic dichotomy in non-carbonaceous and carbonaceous groups [e.g., 3], including oxygen isotope ratios of their constituent chondrules, it is hypothesized chondrules in NC and CCs formed in distinct regions of the protoplanetary disk and subsequently accreted to respective parent asteroids [4, 5]. In contrast, combined O-Cr-Ti isotope studies of chondrules revealed the presence of mm sized chondrule populations with NC-like isotope signatures in CCs, indicating that some fraction of inner Solar System materials (i.e. NC chondrules) was transported outward and into CC chondrule-forming regions [4, 6]. The outward transport of mm sized dust is not consistent with the current understanding of isolated inner and outer Solar System reservoirs, which is inferred based on the isotopic dichotomy of bulk meteorite data [3]. To further investigate potential inner-to-outward disk transport signatures of materials, we conducted oxygen isotope analyses of chondrules in the DOM 08006 CO3.01 carbonaceous chondrite.
Thirty-two chondrules were selected for major element characterization via electron microprobe analysis, as well as oxygen isotope characterization using the WiscSIMS IMS 1280 secondary ion mass spectrometer at the University of Wisconsin-Madison. For SIMS, olivine and pyroxene grains were analyzed in a single session with a 2nA Cs primary ion beam (12 µm in diameter). Plagioclase grains were analyzed in another session with a 20 pA primary ion beam (3µm in diameter). Analytical conditions for both sessions are similar to those described in [7] and [8], respectively.
The DOM 08006 chondrules studied include 20 type I (Mg# > 90, where Mg# = [Mg]/[Mg+Fe] molar %) and 12 type II chondrules (Mg# < 90). The Δ17O values of type I chondrules with Mg# > 98 (N = 10) range from −6 to −4‰ [9]. Most of the other type I (N = 7) and type II (N = 10) chondrules have Δ17O values ranging from −3 to −2‰, which are systematically higher than those in type I chondrules with Mg > 98. The observed Δ17O-Mg# systematics in the DOM 08006 chondrules are similar to those in other pristine carbonaceous chondrites such as CV, CO, and CMs [e.g., 2, 10]. In addition to the universal Δ17O-Mg# trend among the majority of CC chondrules, we also found a distinct population (N = 5) with Δ17O values higher than 0‰, which is not common in the CV, CO, and CMs, but is more consistent with O-isotope signatures of metal-rich CC (CR, CB, CH) or NC chondrules [2]. Among the five 16O-poor chondrules, one chondrule exhibits MnO concentrations and Mg#s of olivine grains that are consistent with those of L3/LL3 type II chondrules, but not those of CR type II chondrules. This suggests that a minor population of chondrules in DOM 08006 either (1) initially formed in a NC reservoir and were then subsequently transported outward to where the parent body of DOM 08006 accreted; or (2) were transported from other CC chondrule-forming regions that produced chondrules with similar MnO-Mg# relationships, such as CH and CB chondrites.
[1] Jones (2012) MAPS 47, 1176-1190. [2] Tenner et al. (2018) In Chondrules, Records of Protoplanetary Disk Processes, 196-246. [3] Kruijer et al. (2020) NatAstron 4, 32-40. [4] Williams et al. (2020) PNAS 117, 23426-23435. [5] Schneider et al. (2020) EPSL 551, 116585. [6] Tenner et al. (2017) MAPS 52, 268-294. [7] Siron et al. (2021) GCA 293, 103-126. [8] Ushikubo et al. (2012) GCA 90, 242-264. [9] Kita et al. (2022) Goldschmidt conference, 10633. [10] Chaumard et al. (2021) GCA 299, 199-218.