TY - JOUR
T1 - Presolar silicates in the matrix and fine-grained rims around chondrules in primitive CO3.0 chondrites
T2 - Evidence for pre-accretionary aqueous alteration of the rims in the solar nebula
AU - Haenecour, Pierre
AU - Floss, Christine
AU - Zega, Thomas J.
AU - Croat, Thomas K.
AU - Wang, Alian
AU - Jolliff, Bradley L.
AU - Carpenter, Paul
N1 - Funding Information:
This study was funded by the NASA Earth and Space Science Fellowship NNX12AN77H (P.H.) and NASA Grants NNX14AG25G (C.F.), NNX12AK47G (T.Z.) and NNX13AM22G (A.W.). We thank the JSC curators and the Meteorite Working Group for the loan of the three meteorite thin sections. We are also grateful to Tim Smolar for maintenance of the NanoSIMS 50 and Auger Nanoprobe at Washington University in St. Louis. We thank Christian Vollmer and an anonymous referee for constructive reviews, as well as comments from associate editor Peter Hoppe, which improved this paper. This work is dedicated to Dr. Ernst Zinner, a pioneer in presolar grain research and secondary-ion mass spectrometry (SIMS). Appendix A
Funding Information:
This study was funded by the NASA Earth and Space Science Fellowship NNX12AN77H (P.H.) and NASA Grants NNX14AG25G (C.F.), NNX12AK47G (T.Z.) and NNX13AM22G (A.W.). We thank the JSC curators and the Meteorite Working Group for the loan of the three meteorite thin sections. We are also grateful to Tim Smolar for maintenance of the NanoSIMS 50 and Auger Nanoprobe at Washington University in St. Louis. We thank Christian Vollmer and an anonymous referee for constructive reviews, as well as comments from associate editor Peter Hoppe, which improved this paper. This work is dedicated to Dr. Ernst Zinner, a pioneer in presolar grain research and secondary-ion mass spectrometry (SIMS).
Publisher Copyright:
© 2017 Elsevier Ltd
PY - 2018/1/15
Y1 - 2018/1/15
N2 - To investigate the origin of fine-grained rims around chondrules (FGRs), we compared presolar grain abundances, elemental compositions and mineralogies in fine-grained interstitial matrix material and individual FGRs in the primitive CO3.0 chondrites Allan Hills A77307, LaPaz Icefield 031117 and Dominion Range 08006. The observation of similar overall O-anomalous (∼155 ppm) and C-anomalous grain abundances (∼40 ppm) in all three CO3.0 chondrites suggests that they all accreted from a nebular reservoir with similar presolar grain abundances. The presence of presolar silicate grains in FGRs combined with the observation of similar estimated porosity between interstitial matrix regions and FGRs in LAP 031117 and ALHA77307, as well as the identification of a composite FGR (a small rimmed chondrule within a larger chondrule rim) in ALHA77307, all provide evidence for a formation of FGRs by accretion of dust grains onto freely-floating chondrules in the solar nebula before their aggregation into their parent body asteroids. Our study also shows systematically lower abundances of presolar silicate grains in the FGRs than in the matrix regions of CO3 chondrites, while the abundances of SiC grains are the same in all areas, within errors. This trend differs from CR2 chondrites in which the presolar silicate abundances are higher in the FGRs than in the matrix, but similar to each other within 2σ errors. This observation combined with the identification of localized (micrometer-scaled) aqueous alteration in a FGR of LAP 031117 suggests that the lower abundance of presolar silicates in FGRs reflects pre-accretionary aqueous alteration of the fine-grained material in the FGRs. This pre-accretionary alteration could be due to either hydration and heating of freely floating rimmed chondrules in icy regions of the solar nebula or melted water ice associated with 26Al-related heating inside precursor planetesimals, followed by aggregation of FGRs into the CO chondrite parent-body.
AB - To investigate the origin of fine-grained rims around chondrules (FGRs), we compared presolar grain abundances, elemental compositions and mineralogies in fine-grained interstitial matrix material and individual FGRs in the primitive CO3.0 chondrites Allan Hills A77307, LaPaz Icefield 031117 and Dominion Range 08006. The observation of similar overall O-anomalous (∼155 ppm) and C-anomalous grain abundances (∼40 ppm) in all three CO3.0 chondrites suggests that they all accreted from a nebular reservoir with similar presolar grain abundances. The presence of presolar silicate grains in FGRs combined with the observation of similar estimated porosity between interstitial matrix regions and FGRs in LAP 031117 and ALHA77307, as well as the identification of a composite FGR (a small rimmed chondrule within a larger chondrule rim) in ALHA77307, all provide evidence for a formation of FGRs by accretion of dust grains onto freely-floating chondrules in the solar nebula before their aggregation into their parent body asteroids. Our study also shows systematically lower abundances of presolar silicate grains in the FGRs than in the matrix regions of CO3 chondrites, while the abundances of SiC grains are the same in all areas, within errors. This trend differs from CR2 chondrites in which the presolar silicate abundances are higher in the FGRs than in the matrix, but similar to each other within 2σ errors. This observation combined with the identification of localized (micrometer-scaled) aqueous alteration in a FGR of LAP 031117 suggests that the lower abundance of presolar silicates in FGRs reflects pre-accretionary aqueous alteration of the fine-grained material in the FGRs. This pre-accretionary alteration could be due to either hydration and heating of freely floating rimmed chondrules in icy regions of the solar nebula or melted water ice associated with 26Al-related heating inside precursor planetesimals, followed by aggregation of FGRs into the CO chondrite parent-body.
KW - Carbonaceous chondrites
KW - Circumstellar grains
KW - Early solar system history
KW - Fine-grained chondrule rims
KW - NanoSIMS
KW - Nebular processes
KW - Pre-accretionary alteration
KW - Presolar grains
KW - Solar Nebula
KW - Stardust
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U2 - 10.1016/j.gca.2017.06.004
DO - 10.1016/j.gca.2017.06.004
M3 - Article
AN - SCOPUS:85021376647
SN - 0016-7037
VL - 221
SP - 379
EP - 405
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -