2008/08/01 by Ian J. Graham, Agnes G. Reyes, Ian C. Wright +3
paper · doi:10.1029/2007jb005453
The NZAPLUME III expedition of September–October 2004 to the northern Kermadec–southern Tofua (NKST) arc, between 28°52′S and 25°07′S, resulted in the discovery of at least seven new submarine volcanic centers and a substantial caldera complex adjacent to the previously known Monowai Seamount. The volcanic centers form a sublinear chain that coincides with the Kermadec Ridge crest in the south (Hinetapeka) and diverges ∼45 km westward of the ridge crest in the north (“V”) just to the south of where the Louisville Ridge intersects with the arc. All of the centers contain calderas or caldera‐like structures, as well as multiple cones, domes, fissure ridges, and vent fields. All show signs of recent eruptive and current hydrothermal activity. There are strong structural controls on edifice location, with cones and fissure ridges typically associated with faulting parallel to the regional ∼12° strike of the arc front. Several of the calderas are ellipsoidal, orientated northwest–southeast in the general direction of least compressive stress. Sampled volcanic rocks, representing the most recently erupted lavas, are all low‐K tholeiites. Two of the centers, Gamble and Rakahore, yielded only high‐silica dacite to rhyolite (69–74 wt% silica), whereas two others, Monowai and “V,” yielded only basalt to andesite (48–63 wt% silica). Mineral assemblages are plagioclase‐pyroxene dominated, with accessory Fe‐Ti oxides, apatite, olivine, and quartz/tridymite/cristobalite, typical of dry volcanic arc systems. Hornblende occurs only in a felsitic rhyolite from Hinepuia volcanic center, and zircon is absent. Glass contents range to 57% in basalts–andesites (mean 20%), and 97% in andesites–rhyolites (mean 59%) and other quench textures, including swallow‐tailed, plumose, or dendritic crystal forms and crystallites, are common. Most lavas are highly vesicular (≤63%; mean 28%) and have low volatile contents (mostly