Economic Geology; January 2005; v. 100; no. 1;
p. 43-61; DOI: 10.2113/100.1.0043
© Society of Economic Geologists
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FIG. 11. Chondrite-normalized rare earth element (REE) plots for a variety of
rocks: (A) the melanocratic rocks and (B) the leucocratic rocks from the
southern Roby zone, (C) the melanonorite and (D) norite and/or leuconorite rocks
from the Twilight zone, and (E) normal and enriched midoceanic ridge basalts (N-
and E-MORB, respectively) compared to the hypothetical parental melt for the
rocks in the southern Roby and Twilight zones. The composition of the
hypothetical melt was calculated following the method of Bédard (1994). Note
the low degrees of REE fractionation for both the bulk rocks and calculated
melt. The calculation of the composition of the hypothetical melt used CIPW
normative minerals of plagioclase, clinopyroxene, orthopyroxene, and olivine.
The remaining is attributed to a trapped melt fraction. Using the REE
concentrations of bulk rocks, the modal abundance of minerals, and partition
coefficients of the minerals and melt, the concentrations of REE in different
phases were calculated using mass balance. We used the concentration of REE in
clinopyroxene and the partition coefficients between clinopyroxene and melt
listed in Bédard (1994) to calculate the REE concentrations of the parental
melt. Chondrite and MORB values are from McDonough and Sun (1995), and Sun and
McDonough (1989), respectively.
Copyright © 2008 by Society of Economic Geologists
