Tetsuro Urabe - Academia.edu (original) (raw)

Papers by Tetsuro Urabe

The Suiyo Seamount on the volcanic front of the Izu-Bonin (Ogasawara) Arc, western Pacific is a d... more The Suiyo Seamount on the volcanic front of the Izu-Bonin (Ogasawara) Arc, western Pacific is a dacitic volcano. There is a hydrothermal field on the floor of the caldera at a depth of 1380 m, where high-temperature fluid is venting through the sediments. A high-temperature hydrothermal system at the Suiyo Seamount has been drilled in June 2001 and in August

Journal of Geography, Aug 18, 2009

Seafloor hydrothermal systems are important in relation to global heat and chemical fluxes as wel... more Seafloor hydrothermal systems are important in relation to global heat and chemical fluxes as well as the distribution of microbial communities within the oceanic crust. From a global context, low-temperature hydrothermal systems located far from the ridge axes are of great importance, because of their large covered area. Our current understandings of seafloor hydrothermal systems come mainly from high-temperature systems on fast-spreading ridges, which are assumed to be typical. Recently, observations have been conducted on high-temperature systems at slow-and ultraslow-spreading ridges. In addition, low-temperature hydrothermal systems far from the ridge axis have been investigated. These findings enable us to obtain a new view of seafloor hydrothermal systems. This paper summarizes recent observational and modeling studies on low-temperature and high-temperature hydrothermal systems. First, we briefly plot seafloor hydrothermal systems and present some historical remarks. Then, we review the most important properties of the crustal structure such as the distribution of heat sources and permeability, which control hydrothermal circulation. These are described in terms of spreading rate. For instance, a hydrothermal system on a fast-spreading ridge is hosted by a quasi-steady magma chamber under the axis, and a system on an ultraslow-spreading ridges is hosted by long-lived tectonic faults at the axis. We also introduce recent numerical simulations both for low-temperature and high-temperature systems including the authors' studies. The main topic of current research is the pattern of circulation of both systems. High-temperature systems are controlled by the phase separation of seawater and the spatial heterogeneities of heat sources. Low-temperature systems instead are mainly affected by the local permeability structure instead. The presence of seamounts is thought to account for heat transport in the oceanic crust.

AGUFM, Dec 1, 2004

ABSTRACT

Eos, Transactions American Geophysical Union, 2002

A high-temperature hydrothermal activity related to dacitic arc magmatism of Suiyo Seamount (28o3... more A high-temperature hydrothermal activity related to dacitic arc magmatism of Suiyo Seamount (28o34'N, 140o38'E), Izu-Ogasawara Arc, western Pacific has been drilled in June 2001 and July 2002 using a tethered, submarine rock-drill system BMS (Benthic Multi-coring System) on-board the R/V Hakurei-Maru # 2 as a part of Archaean Park Project*. Impermeable sheath or cap-rock which consists of clay and anhydrite develops beneath the vent field and traps the end-member fluid within the soft sediment layer 1-3 meters thick beneath the seafloor (Urabe et al., 2002). The sheath is likely to be formed by self-sealing process of anhydrite through cementation of sand grains. Most of the anhydrite from upper part of the cap-rock has sulfur isotopic composition similar to seawater value (+20-21 permil). However, those coexisting with pyrite beneath the cap-rock often have delta34S value as low as +17 permil. Besides, carbon isotope fractionation temperature between CH4 and CO2 is as high as 700oC (Tsunogai et al., 1994). These lines of evidence strongly suggest that the magmatic volatiles are incorporated into end member fluid as important components. Homogeneous chemistry and stable temperature of the end member fluid for a decade indicate that the hydrothermal circulation system is in quasi-stable condition and the oxygenic nature of the dacite magma has strong influence on the relatively higher redox condition of the fluid compared to that of mid-ocean ridge hydrothermal activity. Such a nature may reduce the extent of hydrogen-based sub-vent biosphere at submarine arc volcanoes such as Suiyo Seamount. * Funded by MEXT through the Special Coordination Fund.

OCEANS'11 MTS/IEEE KONA, 2011

We report the preliminary results of the two cruises of ROV (HyperDolphin 3K, operated by JAMSTEC... more We report the preliminary results of the two cruises of ROV (HyperDolphin 3K, operated by JAMSTEC) mapping of sea floor occurrence and in-situ sampling of hydrogenetic ferromanganese deposits. This is the first systematic joint scientific research on the crusts over the deep-sea floors, which unveiled the ubiquitous distribution of the crusts covering the rock substrates. The results of physical measurements

Large amount of hydrogenetic cobalt-rich ferromanganese (Fe-Mn) crusts are known to occur on the ... more Large amount of hydrogenetic cobalt-rich ferromanganese (Fe-Mn) crusts are known to occur on the surface of seamounts or ocean plateaus in the Pacific Ocean. The Fe-Mn crust is one of the most promising seafloor mineral resources enriched in not only Cu, Co, and Ni but also REE and PGE. Here we report the geochemical features of the Fe-Mn crusts collected from the #5 Takuyo Seamount, which is located 120 km west from the Minami-torishima Island, northwestern Pacific.

IODP Scientific Prospectus, 2004

Electronic copies of this series may be obtained from the Integrated Ocean Drilling Program (IODP... more Electronic copies of this series may be obtained from the Integrated Ocean Drilling Program (IODP) Publication Services homepage on the World Wide Web at iodp.tamu.edu/publications.

Ore Geology Reviews, 2017

Ferromanganese crusts cover all outcrops on Takuyo-Daigo seamount traversed during remotely opera... more Ferromanganese crusts cover all outcrops on Takuyo-Daigo seamount traversed during remotely operated underwater vehicle (ROV) dives, except in places covered by foraminifera sand. Takuyo-Daigo is a Cretaceous seamount located in the northwest Pacific Ocean. Geological and bathymetric mapping provide the framework for this study. Chemical and mineralogical analyses of the hydrogenetic ferromanganese crusts show temporal and spatial variations typical of those found in previous studies. Outcrops from 800 to 5500 m water depths are covered with ferromanganese crusts up to 105 mm thick. Beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths, even through the modern oxygen minimum zone (OMZ), contrary to some earlier models for deposition. Growth rates vary from 2.3 to 3.5 mm/Myr, with Fe or Mn fluxes of 0.07-0.11 g/cm 2 /Myr since the early-middle Miocene. Co/Mn ratios decrease with water depth while Fe/Mn and other metallic elements increase or show no change, based on the analysis of the uppermost crust surface. This is probably because Co is the most abundant redox-sensitive element derived from seawater that occurs in crusts.

$Research paper thumbnail of Influence of cell's growth phase on the sulfur isotopic fractionation during in vitro microbial sulfate reduction$

Chemical Geology, 2016

Culture experiments of sulfate reducing bacteria were conducted to produce large sulfur isotope f... more Culture experiments of sulfate reducing bacteria were conducted to produce large sulfur isotope fractionation in marine sediments. We determined the sulfur isotope fractionation factor for both the exponential growth phase and maintenance growth phase. The results show that the sulfur isotope fractionation during the maintenance phase is larger than it is in the exponential phase, irrespective of a temperature anywhere from 25°C to 37°C. In the natural environment, sulfate reducing bacteria may not dominantly grow exponentially. We suggest that sulfate reducers in the natural environment only metabolize at the minimum level to maintain their body. This may solve the apparent discrepancy between the large sulfur isotope fractionation observed in marine sediments and the smaller fractionation obtained from culture experiments.

The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists, 1985

GEOCHEMICAL JOURNAL, 2015

Os isotope compositions in ferromanganese crusts (Fe-Mn crusts) have been used for the dating of ... more Os isotope compositions in ferromanganese crusts (Fe-Mn crusts) have been used for the dating of model ages from present to the Late Cretaceous. This dating method assumes that the Fe-Mn crusts preserve a paleo-seawater Os isotope composition at the timing of Fe-Mn crust deposition. However, available Os isotope data are limited to dredged samples without precise indications of water depths, and the Os isotope variation in relation to water depth remains uncertain. Here, we report on the Os isotope ratio data in the surface layer of Fe-Mn crusts from 956-2987 meters below sea level at the Takuyo Daigo Seamount in the northwestern Pacific Ocean collected by a remotely operated vehicle (ROV). Since the 187 Re/ 188 Os ratios of the surface layer samples exhibited low values ranging from 0.020 to 0.0078, the age correction of the 187 Os/ 188 Os ratios by subtracting radiogenic 187 Os from total 187 Os was not necessary for the Takuyo Daigo Fe-Mn crusts. Regardless of water depth, the surface layer samples possessed a narrow range of 187 Os/ 188 Os ratio (1.003-1.017). As their Os isotope ratios were very similar to or slightly lower than the present-day seawater value (~1.06), the Fe-Mn crusts are inferred to preserve the modern seawater Os isotope composition at the investigated water depths. Therefore, Os isotope stratigraphy using Fe-Mn crusts is a powerful dating tool in paleoceanography.

Journal of Geography (Chigaku Zasshi), 2003

Proceedings of the IODP, 2005

Integrated Ocean Drilling Program Expedition 301 was preceded during 2000 and 2002 by three surve... more Integrated Ocean Drilling Program Expedition 301 was preceded during 2000 and 2002 by three surveys that helped to delineate seafloor and basement relief, sediment thickness, and the nature of ridge-flank hydrothermal conditions and processes on the eastern flank of the Juan de Fuca Ridge. These surveys generated swath map, seismic, and thermal data used to select locations for primary and secondary drilling targets, building from several decades of earlier work. We show compilations and examples of data from several characteristic settings in and around the Expedition 301 work area and use these observations to evaluate sedimentation patterns and thermal conditions in basement. There remain important unanswered questions in this area concerning fluid circulation within the upper oceanic crust, the magnitude of lithospheric heat input, the quantitative significance of advective heat loss from the crust, and relations between basement relief, sedimentation, and sediment alteration. These questions may be resolved through collection of a modest amount of additional data focusing on a few critical locations. Setting, planning, and goals The Endeavour segment of the Juan de Fuca Ridge (JFR) generates lithosphere a few hundred kilometers west of the Olympic Peninsula, Washington State (USA) (Figs. F1, F2). The study area contains structural features common to most ridge flanks: extrusive igneous basement overlain by sediments, abyssal hill topography, high-angle faulting, and basement outcrops. The topographic relief of the young oceanic crust produces barriers to turbidites originating from the continental margin to the east, resulting in the accumulation of thick sediments that bury the eastern flank of the JFR (Davis et al., 1992; Underwood et al., 2005). Igneous basement is exposed to the west, where the crust is young, and the sedimented seafloor to the east is relatively flat, except over basement outcrops. Low-permeability sediment limits advective heat loss from most of the ridge flank, leading to strong thermal, chemical, and alteration gradients in igneous basement. Basement relief is dominated by linear ridges and troughs, oriented subparallel to the spreading center, and was produced mainly by faulting, variations in magmatic supply at the ridge, and off-axis volcanism (Davis and Currie, 1993; Karsten et al., 1998, 1986). Basement relief across this ridge flank tends to be smoother near