Evolution of the winonaite parent body: clues
from silicate mineral trace element
distributions
We have measured the trace element compositions of individual plagioclase, pyroxene and olivine grains in six different winonaites that span the range of textures and mineralogies observed in these meteorites. Textural evidence in these meteorites, including the presence of a plagioclase/clinopyroxene-rich lithology and coarse-grained olivine lithologies, suggests that they may have experienced some silicate partial melting. However, trace element distributions in these lithologies do not show any clear signatures for such an event, possibly indicating an impact origin for these lithologies. Pyroxene trace element compositions do exhibit systematic trends, with abundances generally lowest in Pontlyfni and highest in Winona. The fact that the same trends are present for both incompatible and compatible trace elements suggests, however, that the systematics are more likely to be the result of equilibration of minerals with initially heterogeneous and distinct compositions, rather than partial melting of a compositionally homogeneous precursor. The winonaites have experienced brecciation and mixing of lithologies, followed by varying degrees of thermal metamorphism on their parent body. These factors probably account for the variable bulk REE patterns noted for these meteorites and may have led to re-equilibration of trace elements in different lithologies.
Floss et al. (2008) Meteorit. Planet. Sci., in press.
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Last revised: 12-2007