T. Urabe

Hydrothermal Activity Related to Arc-Backarc Magmatism in the Western Pacific

A compilation of 27 sites of hydrothermal mineralization in the western Pacific was made in terms of their tectonic settings, mineral commodity, and fluid chemistry. These sites constitute about 20% of the known seafloor hydrothermal sites, which are dominated by those occurring at mid-ocean ridges (MORs). High-temperature hydrothermal activities in the western Pacific exclusively occur in association with submarine volcanism found either on backarc spreading centers, backarc rifts, or volcanic fronts in arc-ackarc systems. Magmatic contribution to the hydrothermal systems in arc-backarc settings is more obvious than those in MORs, and several lines of evidence suggest direct interactions between the magma chamber and hydrothermal fluids.

The North Fiji Basin basalts and their magma sources: Part II. Sr-Nd isotopic and trace element constraints

Abstract Sr-Nd isotope and trace element data are reported for basalts from the North Fiji Basin (NFB). NFB basalts are characterized by extreme variations in isotopic ratios and trace element abundances which are related to mantle heterogeneities. Values of 87 Sr 86 Sr for basalts from the northern segments, N160° and triple junction range from 0.7029 to 0.7041, whereas 143 Nd 144 Nd values vary from 0.51281 to 0.51313. Most of the basalts from these segments are characterized by strong relative enrichments in Rb, Ba, Sr, K, Nb, Ta La, Ce and Ti that are comparable to OIB components. The central segments, N15° and N-S have 143 Nd 144 Nd ratios between 0.51298 and 0.51363 and 87 Sr 86 Sr ratios between 0.7029 and 0.7033, and are depleted in large ion lithophile, light rare-earth and high field strength elements similar to N-MORB. Covariation between trace element and isotopic ratios among NFB basalts supports a model in which melts from the NFB rift system are derived by mixing of OIB-type and depleted N-MORB mantle components. The Sr-Nd isotopic and trace element variability indicates that the NFB basalt source is heterogeneous on the scale of individual melt batches.

First cultivation and ecological investigation of a bacterium affiliated with the candidate phylum OP5 from hot springs.

ABSTRACT The phylogenetic group termed OP5 was originally discovered in the Yellowstone National Park hot spring and proposed as an uncultured phylum; the group was afterwards analyzed by applying culture-independent approaches. Recently, a novel thermophilic chemoheterotrophic filamentous bacterium was obtained from a hot spring in Japan that was enriched through various isolation procedures. Phylogenetic analyses of the isolate have revealed that it is closely related to the OP5 phylum that has mainly been constructed with the environmental clones retrieved from thermophilic and mesophilic anaerobic environments. It appears that the lineage is independent at the phylum level in the domain Bacteria. Therefore, we designed a primer set for the 16S rRNA gene to specifically target the OP5 phylum and performed quantitative field analysis by using the real-time PCR method. Thus, the 16S rRNA gene of the OP5 phylum was detected in some hot-spring samples with the relative abundance ranging from 0.2% to 1.4% of the prokaryotic organisms detected. The physiology of the above-mentioned isolate and the related environmental clones indicated that they are scavengers contributing to the sulfur cycle in nature.