Brothers volcano, of the Kermadec intraoceanic arc, is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world. It has two distinct vent fields, known as ...the NW Caldera and Cone sites, whose geology, permeability, vent fluid compositions, mineralogy, and ore-forming conditions are in stark contrast to each other. The NW Caldera site strikes for ∼600 m in a SW–NE direction with chimneys occurring over a ∼145-m depth interval, between ∼1,690 and 1,545 m. At least 100 dead and active sulfide chimney spires occur in this field and are typically 2–3 m in height, with some reaching 6–7 m. Their ages (at time of sampling) fall broadly into three groups: <4, 23, and 35 years old. The chimneys typically occur near the base of individual fault-controlled benches on the caldera wall, striking in lines orthogonal to the slopes. Rarer are massive sulfide crusts 2–3 m thick. Two main types of chimney predominate: Cu-rich (up to 28.5 wt.% Cu) and, more commonly, Zn-rich (up to 43.8 wt.% Zn). Geochemical results show that Mo, Bi, Co, Se, Sn, and Au (up to 91 ppm) are correlated with the Cu mineralization, whereas Cd, Hg, Sb, Ag, and As are associated with the dominant Zn-rich mineralization. The Cone site comprises the Upper Cone site atop the summit of the recent (main) dacite cone and the Lower Cone site that straddles the summit of an older, smaller, more degraded dacite cone on the NE flank of the main cone. Huge volumes of diffuse venting are seen at the Lower Cone site, in contrast to venting at both the Upper Cone and NW Caldera sites. Individual vents are marked by low-relief (≤0.5 m) mounds comprising predominately native sulfur with bacterial mats. Vent fluids of the NW Caldera field are focused, hot (≤300°C), acidic (pH ≥ 2.8), metal-rich, and gas-poor. Calculated end-member fluids from NW Caldera vents indicate that phase separation has occurred, with Cl values ranging from 93% to 137% of seawater values. By contrast, vent fluids at the Cone site are diffuse, noticeably cooler (≤122°C), more acidic (pH 1.9), metal-poor, and gas-rich. Higher-than-seawater values of SO
4
and Mg in the Cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water/rock interactions. Iron oxide crusts 3 years in age cover the main cone summit and appear to have formed from Fe-rich brines. Evidence for magmatic contributions to the hydrothermal system at Brothers includes: high concentrations of dissolved CO
2
(e.g., 206 mM/kg at the Cone site); high CO
2
/
3
He; negative δD and δ
18
O
H2O
for vent fluids; negative δ
34
S for sulfides (to −4.6‰), sulfur (to −10.2‰), and δ
15
N
2
(to −3.5‰); vent fluid pH values to 1.9; and mineral assemblages common to high-sulfidation systems. Changing physicochemical conditions at the Brothers hydrothermal system, and especially the Cone site, occur over periods of months to hundreds of years, as shown by interlayered Cu + Au- and Zn-rich zones in chimneys, variable fluid and isotopic compositions, similar shifts in
3
He/
4
He values for both Cone and NW Caldera sites, and overprinting of “magmatic” mineral assemblages by water/rock-dominated assemblages. Metals, especially Cu and possibly Au, may be entering the hydrothermal system via the dissolution of metal-rich glasses. They are then transported rapidly up into the system via magmatic volatiles utilizing vertical (∼2.5 km long), narrow (∼300-m diameter) “pipes,” consistent with evidence of vent fluids forming at relatively shallow depths. The NW Caldera and Cone sites are considered to represent stages along a continuum between water/rock- and magmatic/hydrothermal-dominated end-members.
Molecular hydrogen (H2) is one of the most important energy sources for subseafloor chemolithoautotrophic microbial ecosystems in the deep‐sea hydrothermal environments. This study investigated ...stable isotope ratios of H2 in 20°–375°C hydrothermal fluids to evaluate usefulness of the isotope ratio as a tracer to explore the H2‐metabolisms. Prior to the observation, we developed an improved analytical method for the determination of concentration and stable isotope ratio of H2. This method achieved a relatively high sensitivity with a detection limit of 1 nmol H2 within an analytical error of 10‰ in the δDH2 value. The δDH2 values in the high‐temperature fluids were between −405‰ and −330‰, indicating the achievement of the hydrogen isotopic equilibrium between H2 and H2O at around the hydrothermal end‐member temperature. In contrast, several low‐temperature fluids showed apparently smaller δDH2 values than those in the high‐temperature fluids in spite of a negligible δDH2 change due to fluid‐seawater mixing, suggesting the possibility of δDH2 change in the low‐temperature fluids and the surrounding environments. Since the δDH2 change in low‐temperature environments is not well explained by the very sluggish abiotic thermal isotopic equilibrium between H2 and H2O, it could be associated with (micro)biological H2‐consuming and/or H2‐generating metabolisms that would strongly promote the isotopic equilibrium at low temperatures. Our first detection of the δDH2 variation in deep‐sea hydrothermal systems presents the availability of the δDH2 value as a new tracer for microbes whose enzymes catalyze D/H exchange in H2.
A block of sulfide crust collected from an active hydrothermal mound in an Archaean site (12°56.4′N, 143°37.9′E; depth ca. 3000 m) of the South Mariana Trough was dated using both 230Th/234U ...disequilibrium and electron spin resonance (ESR) methods to establish the growth duration. Eight subsamples from the sulfide crust were separated further into magnetic and non-magnetic fractions using a Franz isodynamic separator. Thirteen sulfide samples, soluble in nitric acid, yielded 230Th/234U ages of 0.3–2.2 ka. The magnetic fractions had significantly lower Th/U ratios, which enabled age determinations as precise as ±2% (2σ). The age distribution obtained for the section of sulfide crust analyzed is consistent with deposition of sulfide minerals from the upper surface of the crust to the inner side. The 230Th/234U ages of the sulfide minerals were compared with ESR ages of barites separated from 12 subsamples of the same sulfide crust. ESR ages of 0.27–1.3 ka show a spatial pattern broadly resembling that observed in 230Th/234U dating method. While there are some significant offsets, these results illustrate the potential of the two methods for use in investigation of the evolutional history of a hydrothermal system.
► U–Th and ESR dating were applied for hydrothermal samples from South Mariana. ► The samples yieled U–Th ages from 250 to 2000 a and broadly consistent with ESR ages. ► The potential of the two methods in dating hydrothermal deposits has been revealed. ► Sulfide deposits can record the history of hydrothermal activity of >1 ka.
We report horizontal sliding of the kilometre-scale geologic block under the Aso hot springs (Uchinomaki area) caused by vibrations from the 2016 Kumamoto earthquake (Mw 7.0). Direct borehole ...observations demonstrate the sliding along the horizontal geological formation at ~50 m depth, which is where the shallowest hydrothermal reservoir developed. Owing to >1 m northwest movement of the geologic block, as shown by differential interferometric synthetic aperture radar (DInSAR), extensional open fissures were generated at the southeastern edge of the horizontal sliding block, and compressional deformation and spontaneous fluid emission from wells were observed at the northwestern edge of the block. The temporal and spatial variation of the hot spring supply during the earthquake can be explained by the horizontal sliding and borehole failures. Because there was no strain accumulation around the hot spring area prior to the earthquake and gravitational instability could be ignored, the horizontal sliding along the low-frictional formation was likely caused by seismic forces from the remote earthquake. The insights derived from our field-scale observations may assist further research into geologic block sliding in horizontal geological formations.
Ground-water samples were collected from 10 wells in Wadi El-Natrun, Western Desert, Egypt, over four consecutive years. The combination of isotopic composition and hydrochemical analyses was used to ...identify the origin of the groundwater and determine recharging sources as well as to discuss the mechanism controlling hydrochemical variation among wells. Two water sources, a relatively recent/shallow aquifer recharged from Nile River water and a deep/old aquifer (i.e. the Nubian sandstone aquifer system NSAS), are identified from isotopic and geographical relationships and the correlation between isotopic data and bicarbonate concentration. It was found that Nile Delta aquifer water was likely supplied as groundwater flows from the southeast and that old water (paleowater) was supplied upward from deeper layers. Some wells show relatively greater variation in concentration as well as in hydrogen isotope composition during the four-year study. Based on the relationship between concentration and isotope composition the variation was not caused by seawater intrusion or salt dissolution but by intensive water loss. The water loss is not directly due to evaporation or suction but is considered to proceed indirectly within the soil.
•Hydrologic and multi-temporal isotope data have been used to assess the processes affecting water quality in Wadi El-Natrun.•Two water sources are identified from isotopic, geographical and correlation relationships.•High salinity of groundwater is considered to be proceeded indirectly within the soil.
The concentration and stable carbon isotopic composition (δ
13C) of methane have been measured for both seafloor hydrothermal venting fluids and effluent plume waters supplied from the vents at the ...Myojin Knoll Caldera, Izu-Bonin arc, in the western North Pacific. The hydrothermal end-member concentrations and δ
13C of methane show near-homogeneity among vents: 41.2 (μmol/kg) and −16.3 ± 0.8 (‰PDB), respectively, while those in the effluent plume are stratified in the caldera and vertically exhibit a large variation (2.1–11 (nmol/kg) and −29.0 to −11.3 (‰PDB), respectively). Comparison of concentration and δ
13C data between vent fluids and plume waters suggest that the methane is not conserved but microbially oxidized along with the plume. Gradual decrease of diffusive methane flux in proportion to distance from the vent fields supports the occurrence of significant microbial oxidation within the plume. Assuming steady state emission of methane from the vents, (1) kinetic isotope effect due to the microbial oxidation (k
12/k
13); (2) methane flux from the vents (F
vents); (3) heat flux from the vents (Q); and (4) average turnover time of hydrothermal methane (T
all) are estimated to be k
12/k
13 = 1.005 ± 0.001, F
vents = 90–340 (mol/d), Q = 30–110 (MW), and T
all = 60–240 (d), respectively. The estimated turnover times, however, are not uniform within the water column. Around the vents, a turnover time of less than 50 d for methane is one of the shortest values in the pelagic ocean, while those at the distant points correspond to values more typical for deep ocean water.
Effluent hydrothermal water samples in and around the water column of the Suiyo seamount caldera (ca. 2 km diameter), Izu–Bonin arc, were taken to determine concentrations and stable carbon isotopic ...compositions (
δ
13C) of methane (CH
4) and carbon monoxide (CO) in the plume. Venting fluids on the caldera floor (ca. 1370 m depth) were also examined, using the manned submersible Shinkai 2000, to compare the chemical composition and isotopic composition of CH
4 and CO with those in the hydrothermal plume. Strong CH
4 enrichment was detected not only in the water column within the caldera, but also on those outside the caldera at the depth of ca. 1100 m, the sill depth of the caldera wall. Within the plume, we also detected significant CO enrichment. The
δ
13C of CO in the plume, however, exhibited highly
13C-depleted values (−
110‰
VPDB to −
60‰
VPDB) compared with those in seafloor venting hydrothermal fluids (around −
31‰
VPDB). Besides, the plume samples exhibited higher CO
/
CH
4 ratios depending on the distance from the seafloor venting site. We conclude that in situ microbial activity in the plume causes the CO enrichment in the hydrothermal plume. The present results suggest that CO enrichment in deep sea water could act as a new tracer for unidentified seafloor hydrothermal activities, especially for detecting plumes distant from venting sites, as well as for quantifying in situ microbial activity related to CO production in hydrothermal plumes.
We present novel data sets of rare earth element (REE) distributions in a hydrothermal vent field at Yonaguni Knoll IV in the Okinawa Trough. Vertical REE profiles in three water columns showed ...horizontal variation of REE concentrations within 1000–1200 m. Hydrothermal plumes were discovered by anomalous values of methane, manganese and transmissometry at that site. Europium anomalies in the North Pacific deep water (NPDW) (Nozaki et al., 1999) normalized pattern decreased with distance from the hydrothermal vent site, indicating that the dilution of hydrothermal fluid in the plume can be traced using REE. The horizontal variation of negative Ce-anomalies represents the continuous scavenging of REE by suspended matter in the plume. In addition, we measured nine hydrothermal fluid samples. The REE geochemistry of hydrothermal vent systems had been investigated intensively at sediment-starved mid-oceanic ridges, but few studies had examined sediment-hosted hydrothermal systems like those of the Okinawa Trough. The chondrite-normalized REE patterns of the fluids collected at Yonaguni Knoll IV show typical lighter rare earth elements (LREE) and Eu enrichment similar to at the Mid-ocean Ridge sites. A remarkable characteristic of the Yonaguni Knoll IV fluid pattern is its higher concentrations of heavier rare earth elements (HREE) and La composition than the hydrothermal fluids of the sediment-starved East Pacific Rise and Trans-Atlantic Geotraverse. Such a feature is explainable by influences of covering sediments in the back-arc basin Okinawa Trough. At the hydrothermal vent, lighter REE (LREE) in the fluid was reduced systematically during fluid mixing with seawater within the chimney. Light REE elimination resembles fractionation caused by particle scavenging within the water column. However, the lack of Ce depletion, which is a typical REE feature in the water column, along with distinctive Eu reduction, were unique in the Yonaguni Knoll IV fluid, suggesting that fluid REE fractionation at the vent site was induced predominantly by coprecipitation with hydrothermally originated minerals (e.g. sulfate and carbonate), not by adhesive removal by Fe and/or Mn oxide particles. Previous studies had shown that REE removal and fractionation of the hydrothermal system were observed only in deposit samples. Results of this study elucidated REE fractionation in fluid samples using previous analytical data. We were also able to distinguish REE removal mechanisms occurring at the vent site and water column using REE pattern characteristics.
The objective of this research is to clarify the appearance of the teacher community based on collegiality under the GIGA school initiative in Japan. The interview was conducted with 37 teachers in ...12 elementary schools that are relatively advancing ICT use, and we arrived following results; teacher community under the GIGA school initiative is (1) formed by connecting with the existing environment such as a grade group, formal and informal relationship, and physical space of faculty room, (2) struggling to solve problems that have arisen from the installation of the new device, and (3) supported by classroom communities and out-of-school resources because the practical information/knowledge for ICT use is distributed in various places rather than they are concentrated in teacher communities, . However, this appearance of the teacher community is dependent on the school situation. Therefore, each school should find a suitable form of teacher community based on their situation.
The objective of this research is to clarify the appearance of the teacher community based on collegiality under the GIGA school initiative in Japan. The interview was conducted with 37 teachers in ...12 elementary schools that are relatively advancing ICT use, and we arrived following results; teacher community under the GIGA school initiative is (1) formed by connecting with the existing environment such as a grade group, formal and informal relationship, and physical space of faculty room, (2) struggling to solve problems that have arisen from the installation of the new device, and (3) supported by classroom communities and out-of-school resources because the practical information/knowledge for ICT use is distributed in various places rather than they are concentrated in teacher communities, . However, this appearance of the teacher community is dependent on the school situation. Therefore, each school should find a suitable form of teacher community based on their situation.
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