Origin of ferrous zoning in Allende chondrule olivines

Journal Article · Mon Jun 01 04:00:00 EDT 1987 · Geochim. Cosmochim. Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(87)90332-2· OSTI ID:7160222

Peck, J A; Wood, J A

Olivine crystals in Allende Type 1 chondrules have ferrous rims (Fa/sub 15-44/), a few microns thick, at grain surfaces and along crosscutting cracks. This ferrous olivine contains as much as 2 atomic pct. Al and Cr, and 0.2 pct. Ti. Along cracks, profiles of Fe, Al, Cr, and Ti are consistent with diffusional emplacement: these elements moved from an external source through the cracks as a vapor or by grain boundary diffusion, then into the olivine by lattice diffusion. The emplacement did not occur during an epoch of planetary metamorphism that partly equilibrated matrix and chondrule olivines, because (e.g.) neither matrix nor primary magnesian chondrule olivine contains even 1/10 this much, Al, Cr, and Ti. The authors argue that the source of these elements was the nebular gas, and emplacement occurred prior to accretion. The ferrous zones at olivine grain boundaries do not display simple diffusion profiles: rather they appear to be a composite of two concentric rims. The inner rims have compositions similar to those of the ferrous zones along cracks, and contain the highest concentrations of Al, Cr, and Ti. The outer rims are of uniformly high Fa content and relatively low Al, Cr, and Ti concentration. These outer rims appear to be additional material that condensed onto the chondrules after the diffusional emplacement event discussed earlier. Matrix olivine grains, which are identical to these rims in composition, condensed simultaneously.

• Research Organization: Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (USA)
• OSTI ID: 7160222
• Journal Information: Geochim. Cosmochim. Acta; (United States), Journal Name: Geochim. Cosmochim. Acta; (United States) Vol. 51:6; ISSN GCACA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580300 -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400* -- Geochemistry-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMISTRY
CHONDRITES
CHROMIUM
ELEMENTS
GEOCHEMISTRY
IRON COMPOUNDS
IRON SILICATES
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MASS TRANSFER
METALS
METEORITES
MINERALOGY
MINERALS
OLIVINE
ORIGIN
OXYGEN COMPOUNDS
QUANTITATIVE CHEMICAL ANALYSIS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
STONE METEORITES
SURFACE PROPERTIES
TITANIUM
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
ZONING