TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

and over time crustal wall-rocks became armored, which minimized progressive
crustal assimilation.
4.1.1 Geologic Background of the Kerguelen Plateau and Elan Bank
The bulk of the 2 x 10 6 km 2 Kerguelen Plateau formed during the Cretaceous
[31, 32, 42]. Formation of the KP has been ascribed to surfacing of the Kerguelen
plume and is closely spaced in time with the break up of India and Australia at
∼ 132 Ma [80]. Broken Ridge was separated from the KP during the Early Ter-
tiary with the onset of spreading at the Southeast Indian Ridge [109] (Fig. 4.1).
The Kerguelen Plateau has been divided into distinct sections, which include the
Southern KP, Central KP, Northern KP, and Elan Bank [49] (Fig. 4.1). Heard and
McDonald Islands represent the most recent volcanism ascribed to the Kerguelen
plume, and the northerly trending Ninetyeast Ridge has been attributed to Ker-
guelen plume tail volcanism (e.g., [125]). Elan Bank is a salient that extends from
western edge of the KP and contains a number of seismic reflections consistent
with the presence of continental crust [33] (Fig. 4.5). The presence of continental
crust at Elan Bank was confirmed by drilling [33] (Fig. 4.5).
4.2 Samples
Unit 4 consists of a single ∼ 27 m thick variably vesicular subaerial plagioclase
phyric inflated pahoehoe flow [33]. I selected a single sample from a portion of
the Unit 4 flow that exhibited the least alteration and lowest vesicle content (183-
1137A-32R-05W-22-27; Fig. 4.2). Unit 10 is at the bottom of the Site 1137 cored
section. Unit 10 consists of the top of a subaerial massive plagioclase phyric basalt
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