SITE 1190Site 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. 37), 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 ~7172 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. 38). The chemical composition of the single sample analyzed from this site is comparable to the fresh rocks from Site 1188 but is slightly enriched in SiO2 (69.37 wt%) with respect to the fresh sample analyzed from Site 1189.
The limited alteration exhibited by material recovered from Site 1190 is nearly absent, similar to that observed in fresh, near-surface volcanic rocks from Sites 1188 and 1189. The alteration at this site is manifested by poorly devoloped silica ± clay films on vesicle walls and fracture surfaces and rare fine-grained zeolites lining vesicle walls.
Site 1191 | Table of Contents