TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

ent magma requires significant clinopyroxene fractionation (Fig. 2.9). These high
La/Y, relatively evolved liquids, were parental to portions of both xenolith crys-
tals (i.e., 63R2X-1 resorption feature) and phenocrysts. In figure 2.9c the head
of the arrow defining the clinopyroxene crystallization vector corresponds to ap-
proximately 70% clinopyroxene crystallization in terms of La/Y for the highest
MgO Site 1187 Kroenke basalt reported by Fitton and Godard [46]. However, the
amount of crystallization required to account for trace element variations may be
much less given the combined error of calculated partition coefficients (which is
larger for Y than La, Ba, Sr, or Ti), LA-ICP-MS analyses, crystallization tem-
perature, pressure, magmatic H2O, and uncertainties regarding bulk DY and DLa
for clinopyroxene (see error bars in Figs. 2.9, 2.10 and the captions Figs. 2.9,
and 2.10 for details on how the error bars were estimated). The observed major
and trace element variations require magmas both more and less evolved than
those represented by the whole-rock/groundmass. The evolution of these liquids
involved crystallization that was dominated early by plagioclase and olivine (as
suggested by whole-rock and basaltic glass studies) (e.g., Fig. 2.9), although as
noted above, evidence of olivine fractionation is difficult to identify from the pla-
gioclase trace element data presented here [103, 110, 121, 123, 131, 133]. Late
stage clinopyroxene crystallization also played a significant role in evolution of
OJP basaltic magmas, as indicated by variations in La/Y ratios between magma
parental to the high and low An zones. Crystallization of plagioclase from high
temperature, relatively primitive anhydrous magmas at low pressure was an im-
portant process. Conditions to produce the spectrum of relatively evolved and
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