TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

was dominated by late stage clinopyroxene crystallization. I suggest there was
minimal clinopyroxene crystallization outside of the mush layer interstitial spaces.
3.6.5 Ba and Sr variations: Evidence for Polybaric Crystallization?
Plagioclase parent magmas of the three Site 1203 basalts and the single Site
884 basalt I examined plot within fields defined by Detroit Seamount basalts in
Sr vs. Ba space (Fig. 3.14). This indicates there was not significant involvement
of extreme magma compositions such as the low Sr type magmas from Garrett
Transform fault (c.f., [72]). A number of linear trends are apparent in figure 3.14
that can be explained by simple fractional crystallization of olivine and plagio-
clase, which Huang et al. [72] suggested were the dominant crystallizing phases
in DSM tholeiitic basalts. The slope of each fractionation trend is related to the
proportions of plagioclase and olivine during crystallization. The steepest trends
correspond to environments where partial crystallization was dominated by olivine
(Fig. 3.14b, and the shallowest trends in figure 3.14 correspond to environments
where partial crystallization was dominated by plagioclase. Hash marks on the
model lines in figure 3.14b mark 10% increments of fractional crystallization. The
three steepest trends (i.e., olivine dominated) in figure 3.14 consist of Unit 3, 14,
and 31 population B parent magmas, although the majority of Unit 31 population
B parent magmas exhibit a single shallower plagioclase dominated fractionation
trend.
Increased pressure increases Al2O3 in magmas along the olivine gabbro cotectic
[66]. A physical manifestation of this relationship is a greater proportion plagio-
clase in the crystallizing assemblage at increased pressure. Experimental results
have demonstrated that relatively albite-rich plagioclase crystallizes at elevated
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