TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

for Ca by Bindeman et al. [7]. I used equation 4.1 and the “a” and “b” constants
reported for Na by Bindeman et al. [7] to estimate D 1+
0 . Estimation of D 3+
0 is less
straightforward. I assumed D 3+
0 to be ∼ 7.5% of D 2+
0 , which was derived from
experimental data reported in Blundy [9]. I used equation 4.1 and the “a” and
“b” constants reported for Ti by Bindeman et al. [7] to estimate DTi.
4.4 Results
4.4.1 Petrography
Unit 4 plagioclase phenocrysts are typically euhedral and occur as clusters of
crystals but most prominently as individual crystals (Fig. 4.4a). Unit 10 plagio-
clase phenocrysts are large relative to Unit 4 phenocrysts and occur most com-
monly as clusters of euhedral to sub-rounded crystals (Fig. 4.4a). Plagioclase
phenocrysts from both Units 4 and 10 exhibit distinct zonation in cross polar-
ized light (e.g., Figs. 4.8, 4.9). The interiors of plagioclase phenocrysts frequently
exhibit oscillatory type zoning (e.g., crystal 10-1D-A; Fig. 4.9), and most have
obvious core and rim sections. Sections of zoned plagioclase crystals are divided
into three types: 1) cores, 2) intermediate zones, and 3) rims. Dissolution sur-
faces are abundant in crystals from both Units 4 and 10, and frequently enclose
crystal core regions (e.g., Fig. 4.10). Glass and partially crystallized inclusions are
present along some dissolution surfaces. It is important to note that the labeling
of cores and intermediate zones may be purely artificial, as geometric distortions
introduced during sectioning of basalt samples make it difficult to know when a
true crystal core is being sampled [140].
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