Details

Autor(en) / Beteiligte

• Haskin, Larry A.
• Korotev, Randy L.

Titel

Test of a model for trace element partition during closed-system solidification of a silicate liquid

Ist Teil von

• Geochimica et cosmochimica acta, 1977-07, Vol.41 (7), p.921-939

Ort / Verlag

Elsevier Ltd

Erscheinungsjahr

1977

Quelle

Elsevier Journal Backfiles on ScienceDirect (DFG Nationallizenzen)

Beschreibungen/Notizen

• Distributions of trace elements during solidification of a basalt are adequately described by the model of Helmke et al. (1972) for crystallization as a closed system. A hypidiomorphic granular basalt was coarsely crushed to particles < 2 mm in size, was sieved, and materials from nine size fractions were analyzed by neutron activation for REE, Co, Cr, Fe, Hf, Na, Sc, and Ta. Mineral separates from one of the size fractions were also analyzed. Trace-element concentrations of analyzed samples containing statistically significant numbers of mineral grains were matched very well by a mixing model whose end-member components were the analyzed major minerals and mesostasis. Highly accurate modal analyses of the analyzed materials were obtained from the mixing model. Differences in proportions of mesostasis (range 0.57–2%) were shown to be responsible for large differences in trace element concentrations among 0.25–1 g chips from a single hand-specimen of the basalt. Ilmenite in the basalt is badly contaminated with mesostasis. The closed-system model for crystallization yields values for temperature- and composition-averaged distribution coefficients for incompatible elements that are accurate to − 15 to + 30%, and relative to each other are accurate to a few percent. The model demonstrates why some current practices for estimating values of distribution coefficients or of parent liquid compositions lead to errors of factors of several times.