TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

pressure, and growth of An-rich plagioclase is favored in high temperature mag-
mas at lower mean pressure (e.g., [3, 61, 137]). Population B crystals are An-rich
and have parent magmas that make up the steepest fractionation trends in Sr vs.
Ba space, whereas population A parent magmas constitute the shallowest trends
(Fig. 3.14). From this I suggest that population B crystals formed in shallow
magma chambers than population B crystals and were added to magmas carrying
population A crystals either by accumulation (i.e., Site 1203 Units 3 and 31; Site
884 Unit 8) or magma mixing (i.e., Unit 14). Each of the Units I examined from
Site 1203 exhibit evidence of partial crystallization in at least two distinct envi-
ronments, which can be easily explained by polybaric crystallization. Although
my modeling considered only olivine and plagioclase fractionation, small amounts
of clinopyroxene fractionation would not have significantly affected the slopes of
the fractionation trends, as Sr is incompatible and Ba is highly incompatible in
clinopyroxene.
3.7 Summary and Conclusions: Insights Into the Petrogenesis of Depleted De-
troit Seamount Basalts
There is an undeniable role for plagioclase fractionation and accumulation in
the petrogenesis of Detroit Seamount tholeiitic basalts. I see no evidence for a
similar role during the genesis of alkalic basalts (i.e., Site 1203 alkalic basalts
shown in Fig. 13 of Huang et al. [72]). I conclude that the Detroit Seamount
magma chamber system was complex and consisted of extensive mush zones and
multiple interconnected chambers. Evidence of mixing between relatively depleted
and enriched end-member magmas recorded in the hybrid Unit 14 basalt do not
contradict existing models seeking to explain the origin of the depleted component
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