TY - JOUR
T1 - An in situ investigation on the origins and processing of circumstellar oxide and silicate grains in carbonaceous chondrites
AU - Zega, Thomas J.
AU - Haenecour, Pierre
AU - Floss, Christine
N1 - Funding Information:
We are grateful to Christine Floss for her years of collaboration. She was a talented scientist with a dedicated and thorough approach to her research and humble in its delivery. We thank Ann Nguyen and Peter Hoppe for constructive reviews that improved this manuscript. We thank Venkat Manga and Krishna Muralidharan for interesting discussions on thermochemistry. We thank Rhonda Stroud and the Naval Research Laboratory, Washington, DC, for access to the JEOL 2200FS TEM. We acknowledge the NASA Cosmochemistry and Emerging Worlds Programs for supporting our efforts on in?situ investigations of presolar grains over the years including NASA Cosmochemistry grant NNX12AL47G (T.J.Z.) and Emerging Worlds grants NNX15AJ22G (T.J.Z.), 80NSSC19K0509 (T.J.Z.), and NNX14AG25G (C.F.). P.H. acknowledges support from the McDonnell Center for Space Sciences for the NanoSIMS and Auger Nanoprobe work at WUSTL. We acknowledge NASA (grants #NNX12AL47G and #NNX15AJ22G) and NSF (grant #1531243) for funding of the instrumentation in the Kuiper Materials Imaging and Characterization Facility at the Lunar and Planetary Laboratory, University of Arizona. We thank Kay Chang at Thermo Scientific for assistance with operating the ChemiSTEM.
Funding Information:
We are grateful to Christine Floss for her years of collaboration. She was a talented scientist with a dedicated and thorough approach to her research humble in its delivery. We thank Ann Nguyen and Peter Hoppe for constructive reviews that improved this manuscript. We thank Venkat Manga and Krishna Muralidharan for interesting discussions on thermochemistry. We thank Rhonda Stroud and the Naval Research Laboratory, Washington, DC, for access to the JEOL 2200FS TEM. We acknowledge the NASA Cosmochemistry and Emerging Worlds Programs for supporting our efforts on in situ investigations of presolar grains over the years including NASA Cosmochemistry grant NNX12AL47G (T.J.Z.) and Emerging Worlds grants NNX15AJ22G (T.J.Z.), 80NSSC19K0509 (T.J.Z.), and NNX14AG25G (C.F.). P.H. acknowledges support from the McDonnell Center for Space Sciences for the NanoSIMS and Auger Nanoprobe work at WUSTL. We acknowledge NASA (grants #NNX12AL47G and #NNX15AJ22G) and NSF (grant #1531243) for funding of the instrumentation in the Kuiper Materials Imaging and Characterization Facility at the Lunar and Planetary Laboratory, University of Arizona. We thank Kay Chang at Thermo Scientific for assistance with operating the ChemiSTEM.
Publisher Copyright:
© The Meteoritical Society, 2019.
PY - 2020/6/1
Y1 - 2020/6/1
N2 - We report on the isotopic, chemical, and structural properties of four O-rich presolar grains identified in situ in the Adelaide ungrouped C2, LaPaZ Icefield (LAP) 031117 CO3.0, and Dominion Range (DOM) 08006 CO3.0 chondrites. All four grains have oxygen-isotopic compositions consistent with origins in the circumstellar envelopes (CSE) of low-mass O-rich stars evolved along the red-giant and asymptotic-giant branch (RGB, AGB, respectively) of stellar evolution. Transmission electron microscope (TEM) analyses, enabled by focused-ion-beam scanning electron microscope extraction, show that the grain from Adelaide is a single-crystal Mg-Al spinel, and comparison with equilibrium thermodynamic predictions constrains its condensation to 1500 K assuming a total pressure ≤10−3 atm in its host CSE. In comparison, TEM analysis of two grains identified in the LAP 031117 chondrite exhibits different microstructures. Grain LAP-81 is composed of olivine containing a Ca-rich and a Ca-poor domain, both of which show distinct orientations, suggesting changing thermodynamic conditions in the host CSE that cannot be precisely constrained. LAP-104 contains a polycrystalline assemblage of ferromagnesian silicates similar to previous reports of nanocrystalline presolar Fe-rich silicates that formed under nonequilibrium conditions. Lastly, TEM shows that the grain extracted from DOM 08006 is a polycrystalline assemblage of Cr-bearing spinel. The grains occur in different orientations, likely reflecting mechanical assembly in their host CSE. The O-isotopic and Cr-rich compositions appear to point toward nonequilibrium condensation. The spinel is surrounded by an isotopically solar pyroxene lacking long-range atomic order and could have served as a nucleation site for its condensation in the interstellar medium or the inner solar protoplanetary disk.
AB - We report on the isotopic, chemical, and structural properties of four O-rich presolar grains identified in situ in the Adelaide ungrouped C2, LaPaZ Icefield (LAP) 031117 CO3.0, and Dominion Range (DOM) 08006 CO3.0 chondrites. All four grains have oxygen-isotopic compositions consistent with origins in the circumstellar envelopes (CSE) of low-mass O-rich stars evolved along the red-giant and asymptotic-giant branch (RGB, AGB, respectively) of stellar evolution. Transmission electron microscope (TEM) analyses, enabled by focused-ion-beam scanning electron microscope extraction, show that the grain from Adelaide is a single-crystal Mg-Al spinel, and comparison with equilibrium thermodynamic predictions constrains its condensation to 1500 K assuming a total pressure ≤10−3 atm in its host CSE. In comparison, TEM analysis of two grains identified in the LAP 031117 chondrite exhibits different microstructures. Grain LAP-81 is composed of olivine containing a Ca-rich and a Ca-poor domain, both of which show distinct orientations, suggesting changing thermodynamic conditions in the host CSE that cannot be precisely constrained. LAP-104 contains a polycrystalline assemblage of ferromagnesian silicates similar to previous reports of nanocrystalline presolar Fe-rich silicates that formed under nonequilibrium conditions. Lastly, TEM shows that the grain extracted from DOM 08006 is a polycrystalline assemblage of Cr-bearing spinel. The grains occur in different orientations, likely reflecting mechanical assembly in their host CSE. The O-isotopic and Cr-rich compositions appear to point toward nonequilibrium condensation. The spinel is surrounded by an isotopically solar pyroxene lacking long-range atomic order and could have served as a nucleation site for its condensation in the interstellar medium or the inner solar protoplanetary disk.
UR - http://www.scopus.com/inward/record.url?scp=85074989607&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85074989607&partnerID=8YFLogxK
U2 - 10.1111/maps.13418
DO - 10.1111/maps.13418
M3 - Article
AN - SCOPUS:85074989607
SN - 1086-9379
VL - 55
SP - 1207
EP - 1227
JO - Meteoritics and Planetary Science
JF - Meteoritics and Planetary Science
IS - 6
ER -