TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

are thus inconsistent with a typical Hawaii-like emplacement. Huang et al. [72]
suggested Site 884 lavas were erupted closest to the spreading ridge axis and that
the proximity of the Hawaiian hotspot to the ridge at ∼ 81 Ma brought about
greater flow of plume mantle toward the ridge axis prior to mantle partial melting
[72, 119]. They suggest Site 1203 lavas were erupted away from the ridge axis
through hotspot-related lithosphere [72]. It cannot be ruled out that Sites 1203
and 884 sampled separate shield volcanoes (see discussion in [72]). Huang et al.
[72] suggested that all of the Site 1203 lavas came from single volcano, where melts
were segregated at lower mean pressure than Hawaiian volcanoes but higher mean
pressure than Site 884 melts. The sequence of rocks recovered from Site 1203
represent a more diverse record of eruptive styles relative to cored section from
Site 884, as well as several distinct periods of non-deposition or erosion (between
Units 5 and 6, Units 23 and 24, and Units 27 and 28) [128] (Fig. 3.2).
3.3.3 Sampling Strategy
A large proportion of the basalts from Site 1203 and Site 884 contain high
volumes of plagioclase phenocrysts [118, 128]. Regelous et al. [119] noted that this
has a diluting effect on whole-rock compositions. Given the size and volume of the
phenocrysts in the numerous plagioclase phyric basalts from Sites 1203 and 884, it
is apparent that whole-rock compositions of these lavas may be best characterized
as hybrids rather than true liquid compositions. Perhaps of greater significance is
that the plagioclase crystals, which have clearly influenced bulk-rock compositions
([119]), may hold clues to otherwise inaccesible facets of magma evolution.
I measured a total of 14 plagioclase CSDs and two olivine CSDs on 12 separate
lava flows from Site 1203 to examine temporal changes in the physical history of
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