TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

and is most apparent near population B crystal rims where there are changes of up
to > 10 mole % An. Population A and B crystals have thin (< 10 µm) rims that
are as low as An62. The majority of the population A crystals in Unit 3 samples
are unzoned or normally zoned (Fig. 3.7b). There is a small proportion of crystals
exhibiting reverse zonation that have chaotic zoning in their crystal cores that on
average have lower An than the rims (Fig. 3.8b). Small reverse zoned plagioclase
crystals are commonly present in clots of clinopyroxene and plagioclase crystals,
where the small clinopyroxene crystals also exhibit reverse zonation (see inset
image in Fig. 3.8b). Of the two Unit 3 basalt samples I examined, the sample
from the bottom of the flow has a 17% modal abundance of plagioclase and the
sample from the top of the flow has 23% modal plagioclase. I did not measure
olivine modal abundances in the Unit 3 samples but were estimated to be 3-5 %
by Tarduno et al. [128].
3.5.3.2 Site 1203 Unit 14
The Unit 14 basalt I examined has a massive texture and population B crystals
that occur as clusters of euhedral crystals and as occasional individual rounded
crystals (e.g., Fig. 3.7b). Population B crystals exhibit oscillatory zoning (e.g.,
Fig. 3.8e,f) superimposed upon normal zonation with distinct changes in An con-
tent near the rims, often a > 10 mole % An change (e.g., Fig. 3.8e,f). The majority
( 95%) of the population A crystals exhibit the zoning pattern displayed in fig-
ure 3.8g. This pattern, which is characterized by a change from An69−71 in the
core to a thin (2-5 µm) higher An zone then an outermost rim that is An69−71, is
similar to the zoning pattern observed along the rims of the population B crystals
(e.g., rims in Figs. 3.8e,f vs. Fig. 3.8g). The remaining proportion of the pop-
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