The objectives for Site 1190 (see Figs. F7, F25) were obtaining information on the volcanic architecture of Pual Ridge and fresh material for comparisons with the altered rocks recovered at other sites. Additionally, results obtained earlier during Leg 193 suggested that hydrothermal alteration might be more intense and widespread than previously thought. It is possible that at Site 1190 below a few tens of meters of fresh or incipiently altered rocks lie deeply altered counterparts. However, because of technical and logistical difficulties, we were not able to fully address these objectives.
Holes 1190A, 1190B, and 1190C provided a total of 110 cm of core, representing material from the upper 17 m of the volcanic edifice of Pual Ridge. Almost all of the rocks recovered are fresh, black, glassy, moderately vesicular, plagioclase-clinopyroxene ± magnetite/phyric rhyodacite (Fig. F38), but a couple of pieces show incipient bleaching. The felsic composition of the samples has been confirmed by measurements of the refractive index of the glass, which indicate a SiO2 content of ~71-72 wt%. Clusters of several phenocrysts, including two or three phenocryst phases, are common, and the glassy groundmass that occupies interstitial and concave spaces in and around these clusters is usually free or nearly free of microlites, in contrast to the microlite-rich glassy mesostasis elsewhere in the rocks (Fig. F39). The chemical composition of the single sample analyzed from this site is comparable to the fresh rocks from Sites 1188 and 1191 but is enriched in SiO2 (70 wt% on an anhydrous basis) with respect to the fresh sample analyzed from Site 1189.
The alteration exhibited by material recovered from Site 1190 is limited to poorly developed silica ± clay films on vesicle walls and fracture surfaces and rare fine-grained zeolites lining vesicle walls. This is similar to the alteration observed in fresh near-surface volcanic rocks from Sites 1188 and 1189.