TY - JOUR
T1 - A petrologic and microstructural study of a compact type A calcium-aluminum-rich inclusion from the Northwest Africa 5028 CR2 chondrite
T2 - Implications for nebular and parent-body processes
AU - Ramprasad, Tarunika
AU - Haenecour, Pierre
AU - Domanik, Kenneth
AU - Zega, Thomas J.
N1 - Funding Information:
This research was funded by NASA grants #NNX15AJ22G and #80NSSC19K0509. We acknowledge NASA grants #NNX12AL47G and #NNX15AJ22G, and NSF grants #1531243 and #0619599 for funding of the instrumentation in the Kuiper Materials Imaging and Characterization Facility at the Lunar and Planetary Laboratory, University of Arizona. We thank Prajkta Mane at the Lunar and Planetary Institute (USRA) and Laurence A. J. Garvie at the Center of Meteorite Studies, Arizona State University for their help with selection of the petrographic section. We thank Dr. Jerry Chang at the Kuiper Materials Imaging and Characterization Facility at the Lunar and Planetary Laboratory, University of Arizona, for help with analyzing the samples. We thank Laura Seifert and Drs. Krishna Muralidharan and Venkateswara Manga at the University of Arizona for insightful discussions that helped improve the manuscript. We also thank AE Adrian Brearley and two anonymous referees for constructive reviews that improved the paper.
Funding Information:
This research was funded by NASA grants #NNX15AJ22G and #80NSSC19K0509. We acknowledge NASA grants #NNX12AL47G and #NNX15AJ22G, and NSF grants #1531243 and #0619599 for funding of the instrumentation in the Kuiper Materials Imaging and Characterization Facility at the Lunar and Planetary Laboratory, University of Arizona. We thank Prajkta Mane at the Lunar and Planetary Institute (USRA) and Laurence A. J. Garvie at the Center of Meteorite Studies, Arizona State University for their help with selection of the petrographic section. We thank Dr. Jerry Chang at the Kuiper Materials Imaging and Characterization Facility at the Lunar and Planetary Laboratory, University of Arizona, for help with analyzing the samples. We thank Laura Seifert and Drs. Krishna Muralidharan and Venkateswara Manga at the University of Arizona for insightful discussions that helped improve the manuscript. We also thank AE Adrian Brearley and two anonymous referees for constructive reviews that improved the paper.
Publisher Copyright:
© 2022 The Meteoritical Society.
PY - 2022/10
Y1 - 2022/10
N2 - Compact type A calcium-aluminum-rich inclusions (CTA CAIs) are believed to have experienced partial melting that erased all information on their original nebular condensation. To investigate this question, we report new microstructural data on a CTA CAI, composed primarily of melilite, spinel, and perovskite, in the Northwest Africa 5028 CR2 chondrite. The melilite grains contain low (5–10 mole%) åkermanite contents and are not compositionally zoned. Spinel and perovskite each occur as near endmember compositions MgAl2O4 and CaTiO3 and contain minor V and Al, respectively. A continuous rim composed of melilite, spinel, and perovskite, with minor hibonite grains occur around the CAI. We extracted two regions of interest from the interior CAI and two from the rim using focused ion beam techniques for detailed analysis using transmission electron microscopy. Evidence for thermal processing occurs as a perovskite–spinel–spinel triple junction in an interior section and a spinel inclusion within perovskite in a rim section. Evidence for parent-body alteration occurs in the form of Fe-rich sheet silicates in the rim, and localized amstallite in the interior of the CAI. While previous work suggested that many CTA CAIs experienced thermal processing in the solar nebula, including partial melting, our data show that signatures of primary condensation can be preserved in the form of more refractory phases contained within less refractory minerals, namely melilite and perovskite grains within spinel, and hibonite grains within perovskite, respectively. The inclusion we report on here has a complex history involving gas-phase condensation, nebular thermal processing, and parent-body alteration.
AB - Compact type A calcium-aluminum-rich inclusions (CTA CAIs) are believed to have experienced partial melting that erased all information on their original nebular condensation. To investigate this question, we report new microstructural data on a CTA CAI, composed primarily of melilite, spinel, and perovskite, in the Northwest Africa 5028 CR2 chondrite. The melilite grains contain low (5–10 mole%) åkermanite contents and are not compositionally zoned. Spinel and perovskite each occur as near endmember compositions MgAl2O4 and CaTiO3 and contain minor V and Al, respectively. A continuous rim composed of melilite, spinel, and perovskite, with minor hibonite grains occur around the CAI. We extracted two regions of interest from the interior CAI and two from the rim using focused ion beam techniques for detailed analysis using transmission electron microscopy. Evidence for thermal processing occurs as a perovskite–spinel–spinel triple junction in an interior section and a spinel inclusion within perovskite in a rim section. Evidence for parent-body alteration occurs in the form of Fe-rich sheet silicates in the rim, and localized amstallite in the interior of the CAI. While previous work suggested that many CTA CAIs experienced thermal processing in the solar nebula, including partial melting, our data show that signatures of primary condensation can be preserved in the form of more refractory phases contained within less refractory minerals, namely melilite and perovskite grains within spinel, and hibonite grains within perovskite, respectively. The inclusion we report on here has a complex history involving gas-phase condensation, nebular thermal processing, and parent-body alteration.
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U2 - 10.1111/maps.13910
DO - 10.1111/maps.13910
M3 - Article
AN - SCOPUS:85138567532
VL - 57
SP - 1936
EP - 1956
JO - Meteoritics and Planetary Science
JF - Meteoritics and Planetary Science
SN - 1086-9379
IS - 10
ER -