TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

3.5 Results
3.5.1 Crystal Size Distributions
3.5.1.1 Site 1203 CSDs
Plagioclase CSDs of Site 1203 basalts are categorized as linear, gently curved
upward, or strongly kinked upward (Fig. 3.4). Of the 12 separate flows I sampled
from Site 1203, two flows: Units 14 and 31, have strongly upward kinked CSDs. A
number of flows have plagioclase CSDs that are gently curved upward, including
Unit 3 (top), Unit 8, Unit 18, and Unit 19. Each of these flows, with the exception
of Unit 19, are tholeiitic pillow basalts (Fig. 3.4). Unit 19 is a subaerial alkalic
basalt, is the youngest alkalic basalt sampled at Site 1203, and is the closest to
the alkalic to tholeiitic basalt transition. Three submarine tholeiitic sheet flows
were examined (Units 11, 16, and 24), and each have linear plagioclase CSDs. The
Unit 11 and Unit 16 tholeiitic sheet lobes have linear olivine CSDs with slopes
nearly identical to their corresponding plagioclase CSDs (Fig. 3.4, Table 3.2). I
sampled two site 1203 basalts near flow tops and bottoms. Unit 3, which is a ∼
25 m thick tholeiitic pillow basalt, and Unit 23, which is a ∼ 62 m thick alkalic
compound pahoehoe basalt flow. The plagioclase CSD of the top of Unit 3 is
curved gently upward (Fig. 3.4b) but otherwise has a nearly identical slope to the
CSD from the bottom of the flow. Samples from both the top and bottom of Unit
23 have linear plagioclase CSDs but the sample from the top of the flow has a
distinctly shallower slope (Fig. 3.4i). Below the alkalic to tholeiitic transition a
larger proportion of the flows I examined have linear CSDs (Fig. 3.4).
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