TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

one is then to relate DSM basalt chemistry to the nature of a mantle source region
or some mantle process, it is vital to understand the extent to which bulk DSM
magma compositions were influenced during their transit through the crust. Once
the extent of magma evolution in the shallow crust is constrained, understanding
the roles of mantle processes becomes less convoluted. I employ an integrated tex-
tural and microanalytical approach to constrain shallow magma evolution during
the formation of Detroit Seamount by 1) identification of crystal populations with
related physical growth histories and 2) understanding the provenance of these
crystals.
Hypothesis 1: Magma mixing occurred between OIB and MORB magmas,
as the Hawaiian plume was close to a MOR [95]. If this is the case, evidence
supporting magma mixing, such as curved CSDs (e.g., [67]) from mixed crystal
populations (e.g., [139]) should be apparent. If magma mixing did occur, and
the plume-ridge proximity was least when the Site 884 (∼81 Ma) basalts were
erupted. These basalts should contain a better record of mixing relative to Site
1203 (∼75 Ma) basalts. Plagioclase crystals grown after the mixing event will
reflect the trace element and isotopic composition of the hybridized melt and will
appear in textural equilibrium with the melt. Zones grown before the mixing
event will bear the trace element and isotopic compositions of respective mixing
end-members. Some crystals may contain compositional evidence of exposure and
growth end-member magmas.
Hypothesis 2: The ascending OIB plume punched through and entrained
MORB source rocks as well as MORB intrusive and extrusive rocks. Melting of
the source rocks prior to plagioclase crystallization would have led to MORB-like
signatures in initial growth zones in crystals from the oldest plagioclase popu-
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