Journal
GEOCHIMICA ET COSMOCHIMICA ACTA
Volume 184, Issue -, Pages 151-172Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.gca.2016.04.018
Keywords
Spinel-hibonite inclusions (SHIBs); CAI; Meteorites; Solar nebula; Oxygen isotopes; Internal isochrons; Aluminum-26; Magnesium isotopes; Titanium isotopes; Calcium isotopes
Categories
Funding
- NASA [NNX09AG39G, NNX15AF78G, NNX11AG62G, NNX14AG29G, NNX13AD15G, NNX15AH38G]
- NSF [EAR03-19230, EAR10-53466, EAR13-55590]
- Tawani Foundation
- NASA Earth and Space Science Fellowship
- Division Of Earth Sciences
- Directorate For Geosciences [1355590] Funding Source: National Science Foundation
- NASA [683990, 475912, NNX15AF78G, NNX15AH38G, 804135, NNX14AG29G, NNX13AD15G, 804520] Funding Source: Federal RePORTER
Ask authors/readers for more resources
We report oxygen, calcium, titanium and Al-26-Mg-26 isotope systematics for spinel-hibonite inclusions (SHIBs), a class of calcium-aluminum-rich inclusions (CAI) common in CM chondrites. In contrast to previous studies, our analyses of 33 SHIBs and four SHIB-related objects obtained with high spatial resolution demonstrate that these CAIs have a uniform Delta O-17 value of approximately -23 parts per thousand, similar to many other mineralogically pristine CAIs from unmetamorphosed chondrites (e.g., CR, CV, and Acfer 094). Five SHIBs studied for calcium and titanium isotopes have no resolvable anomalies beyond 3 sigma uncertainties. This suggests that nucleosynthetic anomalies in the refractory elements had been significantly diluted in the environment where SHIBs with uniform Delta O-17 formed. We established internal Al-26-Mg-26 isochrons for eight SHIBs and found that seven of these formed with uniformly high levels of Al-26 (a multi-CAI mineral isochron yields an initial Al-26/Al-27 ratio of similar to 4.8 x 10(-5)), but one SHIB has a smaller initial Al-26/Al-27 of similar to 2.5 x 10(-5), indicating variation in Al-26/Al-27 ratios when SHIBs formed. The uniform calcium, titanium and oxygen isotopic characteristics found in SHIBs with both high and low initial Al-26/Al-27 ratios allow for two interpretations. (1) If subcanonical initial Al-26/Al-27 ratios in SHIBs are due to early formation, as suggested by Liu et al. (2012), our data would indicate that the CAI formation region had achieved a high degree of isotopic homogeneity in oxygen and refractory elements before a homogeneous distribution of Al-26 was achieved. (2) Alternatively, if subcanonical ratios were the result of Al-26-Mg-26 system resetting, the clustering of SHIBs at a Delta O-17 value of similar to-23 parts per thousand would imply that a O-16-rich gaseous reservoir existed in the nebula until at least similar to 0.7 Ma after the formation of the majority of CAIs. (C) 2016 Elsevier Ltd. All rights reserved.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available