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doi:10.2204/iodp.proc.301.205.2008

Results

Table T1 summarizes the results of N₂ and Ar analyses. One sample was only analyzed with N₂, five were analyzed with both gases, and seven were only analyzed with Ar. In our samples, SSAs measured with Ar were smaller than those measured with N₂ for the same samples, and replicates measured with Ar had a smaller standard deviation, so that adsorbate was preferentially used. For samples that were measured with both adsorbates, SSA using Ar was roughly 50% of the value measured with N₂, which is consistent with previously reported differences between N₂ and Kr (Anbeek, 1992; Brantley and Mellott, 2000). The SSAs of the 12 samples analyzed with Ar ranged from 0.3 to 52 m²/g. The samples represent three lithologies: breccia (two samples), pillow basalt (seven samples), and massive flow (three samples). The two breccia samples (mean SSA = 40.5 ²/g) were highly altered and had a significantly higher SSA than the pillow and flow basalt samples (mean SSA = 2.3 ²/g).

Figure F1 shows a typical plot of the adsorption and desorption isotherms from our samples. Because of instrument limitations, we obtained desorption isotherms only for samples analyzed with N₂. The combination of isotherm shape and hysteresis is an indicator of mesoporosity: pore diameters between 2 and 50 nm (Gregg and Sing, 1982; Rouquerol et al., 1994; Sing et al., 1985). The hysteresis loop matches type H3 and was observed for all samples for which we obtained desorption data, which is characteristic of slit-shaped pores or platelike particles. The low-pressure hysteresis (P/P₀ < 0.4) is unusual and does not generally occur in laboratory ground samples. It is probably because of the long run time for these samples (~13 h per sample) and the fact that liquid nitrogen used to cool the samples would evaporate over time. As recommended by Gregg and Sing (1982), we checked the repeatability of all our measurements to ensure that no changes were occurring to our samples because of the adsorption procedure. Figure F1 illustrates the repeatability of measurements for the sample from Section 301-U1301B-3R-1 using both nitrogen and argon.

Figure F2 shows the correlations between SSA and three physical properties and sample depth. The strongest correlation is with porosity (R² = 0.73, P ≤ 0.05), which shows a positive, roughly linear trend. There are also qualitative negative correlation relationships between SSA and bulk density and between SSA and seismic velocity. The sample from Section 301-U1301B-18R-2 was collected from a vesicular massive unit and had the second highest porosity of all our samples but had a lower than average BET SSA and was only lightly altered (Table T1). We interpret this as evidence that BET SSA is independent of macroscale porosity such as vesicles and instead is controlled by increased porosity because of secondary mineral formation. The same sample also appeared to be an outlier in the correlation of BET SSA with bulk density and P-wave velocity. Although not quantitative, increased BET SSA correlates with increased alteration in all the physical property plots.

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