TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

microdrilling, a pre-cleaned square 4 cm x 4 cm piece of parafilm with a ∼ 2 cm
center hole was adhered to the polished sample surface. A droplet of ultrapure
water was then placed over the center hole and area to be drilled. The parafilm
was was used to minimize dispersion of the water droplet and to minimize sample
loss. Microdrilling was then performed within the water droplet, which generated
a slurry as sample material was removed. The slurry was removed using a mi-
cropipette and placed in a 3.5 mL Teflon beaker. The sample was then subjected
to a hotplate concentrated HF and HNO3 digestion. Strontium was extracted
using a scaled down ion exchange column method. Extracted Sr was loaded on
Re filaments and 87 Sr/ 86 Sr ratios were measured using a Finnigan Triton thermal
ionization mass spectrometer (TIMS). Davidson et al. [39] and Tepley et al. [135]
provide more extensive discussions about of the micro-Sr isotope method.
1.7 Project Introductions
1.7.1 The Ontong Java Plateau, SW Pacific Ocean
The Ontong Java Plateau is the worlds largest oceanic LIP spanning an area
of roughly 2.018 x 10 6 km 2 in the Southwest Pacific ocean [30, 32, 93, 94, 132, 133]
(Fig. 1.4). Tarduno et al. [129] and Mahoney et al. [93, 94] suggested that the
bulk of the OJP formed in a submarine eruptive environment relatively rapidly
around ∼122 Ma, with a minor event at ∼90 Ma [93, 94, 132, 133]. Most of the
OJP is presently submerged, exceptions being the southern plateau margin on
the islands of Malaita, San Cristobal (Makira), and Santa Isabel in the Solomon
Islands, where obducted segments now outcrop [116].
Despite its size, only three subtly different low-K tholeiitic basalt types have
been recovered from the OJP, either by field work or ocean drilling, which have
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