Computer Science
Scientific paper
Mar 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997m%26ps...32..217t&link_type=abstract
Meteoritics, vol. 32, pages 217-230
Computer Science
7
Scientific paper
The cumulate eucrite meteorites are gabbros that are related to the eucrite basalt meteorites. The eucrite basalts are relatively primitive (nearly flat REE patterns with La ~ 8-30 3 CI), but the parent magmas of the cumulate eucrites have been inferred as extremely evolved (La to > 100 3 CI). This inference has been based on mineral/magma partitioning, and on mass balance considering the cumulate eucrites as adcumulates of plagioclase + pigeonite only; both approaches have been criticized as inappropriate. Here, mass balance including magma + equilibrium pigeonite + equilibrium plagioclase is used to test a simple model for the cumulate eucrites: that they formed from known eucritic magma types, that they consisted only of magma + crystals in chemical equilibrium with the magma, and that they were closed to chemical exchange after the accumulation of crystals. This model is tested for major and rare earth elements (REE). The cumulate eucrites Serra de Mag and Moore County are consistent, in both REE and major elements, with formation by this simple model from a eucrite magma with a composition similar to the Nuevo Laredo meteorite: Serra de Mag as 14% magma, 47.5% pigeonite, and 38.5% plagioclase; Moore County as 35% magma, 37.5% pigeonite, and 27.5% plagioclase. These results are insensitive to the choice of mineral/magma partition coefficients. Results for the Moama cumulate eucrite are strongly dependent on choice of partition coefficients; for one reasonable choice, Moama's composition can be modeled as 4% Nuevo Laredo magma, 60% pigeonite, and 36% plagioclase. Selection of parent magma composition relies heavily on major elements - the REE cannot uniquely indicate a parent magma among the eucrite basalts. The major element compositions Y-791195 can be fit adequately as a simple cumulate from any basaltic eucrite composition. However, Y791195 has LREE abundances and La/Lu too low to be accommodated within the model using any basaltic eucrite composition and any reasonable partition coefficients. Post-cumulus loss of incompatible elements seems possible. It is intriguing that Serra de Mag, Moore County, and Moama are consistent with the same parental magma - could they be from the same igneous body on the eucrite parent asteroid (4 Vesta)?
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