Detailed airborne magnetic studies conducted over the region of the S.W. Pacific marginal basins extending from the Solomon Islands to New Zealand suggest that three major phases of basin formation and island arc development have occurred in this region. Development of the Tasman Sea took place during the Late Cretaceous‐Paleocene. Development of the basins to the east of the Tasman Sea occurred predominantly during the Oligocene as well as during the Upper Miocene to Recent. The South Fiji Basin, consisting of the Kupe and Minerva Abyssal Plains, is marked by the presence of possibly two RRR triple junction spreading centers that were active between the times of anomalies 13 to 7 (36–25.5 m.y.). The Kupe Abyssal Plain shows the presence of residual magnetic anomalies 7 to 13 of the eastern limb of the proposed spreading center. The western limb appears to have been subducted beneath the present site of the Three Kings Rise. This seafloor spreading phase (calculated half‐spreading rate of 35 mm/yr) was coincident with the overthrusting phase of the New Caledonia ultramafic rocks. During that period, active volcanism along the then continuous Solomons‐New Hebrides‐Fiji‐Lau Island arc was taking place. Magnetic anomalies from 1 to 4 (0–8 m.y. B.P.) are seen to extend along a clearly defined lineation pattern over the North Fiji Basin. Analysis of the magnetic anomalies suggests that during the Upper Miocene, at about the time of magnetic anomaly 4 (8 m.y.), the Solomons–Lau Island arc commenced breaking up through the development of an active spreading center (calculated half‐spreading rate of 35 mm/yr) located between the New Hebrides and Fiji portions of the island arc. Portions of the northeastern sector of the Minerva Abyssal Plain were subducted beneath the North Fiji Basin during this period between 0–8 m.y. B.P. At the time of about anomaly 3 to 2′ (4.5–3.5 m.y.) the development of the North Fiji Basin extended into the Lau Basin and Havre Trough, thus separating the Tonga and Lau Ridges. As a result, a distinct series of active spreading centers developed southward along the axis of the Havre Trough–Lau Basin. The Havre Trough is marked by present seismic and submarine volcanic activity. Residual magnetic anomalies 1–2 (0–1.8 m.y. B.P.) form a symmetrical pattern around the axis of the trough extending south from the Lau Basin to the active Taupo‐White Island Volcanic Zone of New Zealand. Phases of development of the marginal basins described in this paper may be correlated with phases of changes in the direction and rate of Pacific Plate motion.
We report the complete genome sequence of the deep-sea ␥-proteobacterium, Idiomarina loihiensis, isolated recently from a hydrothermal vent at 1,300-m depth on the Lo ihi submarine volcano, Hawaii. The I. loihiensis genome comprises a single chromosome of 2,839,318 base pairs, encoding 2,640 proteins, four rRNA operons, and 56 tRNA genes. A comparison of I. loihiensis to the genomes of other ␥-proteobacteria reveals abundance of amino acid transport and degradation enzymes, but a loss of sugar transport systems and certain enzymes of sugar metabolism. This finding suggests that I. loihiensis relies primarily on amino acid catabolism, rather than on sugar fermentation, for carbon and energy. Enzymes for biosynthesis of purines, pyrimidines, the majority of amino acids, and coenzymes are encoded in the genome, but biosynthetic pathways for Leu, Ile, Val, Thr, and Met are incomplete. Auxotrophy for Val and Thr was confirmed by in vivo experiments. The I. loihiensis genome contains a cluster of 32 genes encoding enzymes for exopolysaccharide and capsular polysaccharide synthesis. It also encodes diverse peptidases, a variety of peptide and amino acid uptake systems, and versatile signal transduction machinery. We propose that the source of amino acids for I. loihiensis growth are the proteinaceous particles present in the deep sea hydrothermal vent waters. I. loihiensis would colonize these particles by using the secreted exopolysaccharide, digest these proteins, and metabolize the resulting peptides and amino acids. In summary, the I. loihiensis genome reveals an integrated mechanism of metabolic adaptation to the constantly changing deep-sea hydrothermal ecosystem.hydrothermal vent
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