The Origin of Refractory Minerals in Comet 81P/Wild 2
Refractory Ti-bearing minerals in the calcium-, aluminium-rich inclusion (CAI) Inti, recovered from the comet 81P/Wild 2 sample, were examined using analytical (scanning) transmission electron microscopy (STEM) methods including imaging, nanodiffraction, energy dispersive spectroscopy (EDX) and electron energy loss spectroscopy (EELS). Inti fassaite (Ca(Mg,Ti,Al)(Si,Al){sub 2}O{sub 6}) was found to have a Ti{sup 3+}/Ti{sup 4+} ratio of 2.0 {+-} 0.2, consistent with fassaite in other solar system CAIs. The oxygen fugacity (log f{sub O{sub 2}}) of formation estimated from this ratio, assuming equilibration among phases at 1509K, is -19.4 {+-} 1.3. This value is near the canonical solar nebula value (-18.1 {+-} 0.3) and in close agreement with that reported for fassaite-bearing Allende CAIs (-19.8 {+-} 0.9) by other researchers using the same assumptions. Nanocrystals of osbornite (Ti(V)N), 2-40 nm in diameter, are embedded as inclusions within anorthite, spinel and diopside in Inti. Vanadium is heterogeneously distributed within some osbornite crystals. Compositions range from pure TiN to Ti{sub 0.36}V{sub 0.64}N. The possible presence of oxide and carbide in solid solution with the osbornite was evaluated. The osbornite may contain O but does not contain C. The presence of osbornite, likely a refractory early condensate, together with the other refractory minerals in Inti, indicates that the parent comet contains solids that condensed closer to the proto-sun than the distance at which the parent comet itself accreted. The estimated oxygen fugacity and the reported isotopic and chemical compositions are consistent with Inti originating in the inner solar system as opposed to it being a surviving CAI from an extrasolar source. These results provide insight for evaluating the validity of models of radial mass transport dynamics in the early solar system. The oxidation environments inferred for the Inti mineral assemblage are inconsistent with an X-wind formation scenario. In contrast, radial mixing models allowing accretion of components from different heliocentric distances can satisfy the observations from the cometary CAI Inti.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 966546
- Report Number(s):
- LLNL-JRNL-410054
- Journal Information:
- Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 23 Vol. 73; ISSN GCACAK; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
Similar Records
Metasomatic alteration of coarse‐grained igneous calcium‐aluminum‐rich inclusions from CK3 carbonaceous chondrites
Infiltration metasomatism of the Allende coarse-grained calcium-aluminum-rich inclusions
Related Subjects
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
99 GENERAL AND MISCELLANEOUS
ANORTHITE
CALCIUM
CARBIDES
CHEMICAL COMPOSITION
COMETS
DIOPSIDE
ELECTRONS
ENERGY-LOSS SPECTROSCOPY
ORIGIN
OXIDATION
OXIDES
OXYGEN
SOLAR NEBULA
SOLAR SYSTEM
SOLID SOLUTIONS
SPECTROSCOPY
SPINELS
TRANSMISSION ELECTRON MICROSCOPY
TRANSPORT
VANADIUM