45 research outputs found
Concentrations of amino acids in hydrothermal sediments collected from the Izena and Yoron Cauldrons, Okinawa Trough
Leaching of metals and metalloids from hydrothermal ore particulates and their effects on marine phytoplankton
http://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt11-15/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt12-06/
Postseismic fluid discharge chemically recorded in altered pseudotachylyte discovered from an ancient megasplay fault: an example from the Nobeoka Thrust in the Shimanto accretionary complex, SW Japan
Abstract Megasplay fault branching from plate boundaries of subduction zones is thought to be important sources of earthquakes and tsunamis. In this study, we performed structural and geochemical analyses on a fossilized megasplay fault (the Nobeoka Thrust of the Shimanto accretionary complex) to understand fluid-rock interaction and how the splay fault plays a role in fluid flow in the seismogenic zone. As a result of structural observations, we report that the principal slip zone (PSZ) of the Nobeoka Thrust is composed of foliated cataclasite originating from a sandstone-shale mélange and includes a thin (~ 1.5 mm thick) pseudotachylyte layer. Major and trace element composition analysis and EPMA element mapping revealed that the pseudotachylyte is enriched in Li and Cs within the PSZ, as well as in the slip zone of a minor fault in the footwall. Li and Cs enrichment in pseudotachylyte is interpreted as a result of fluid-rock interaction in the postseismic stage, because such an anomaly only results from a large fluid/rock ratio (R > 512–24 at 250–350 °C) under the influence of Li- and Cs-enriched fluids. The amount of fluid that reacted with the pseudotachylyte is estimated to be 1.78 × 100 to 7.61 × 103 m3
Changes in illite crystallinity within an ancient tectonic boundary thrust caused by thermal, mechanical, and hydrothermal effects: an example from the Nobeoka Thrust, southwest Japan
Simultaneous estimation of in situ porosity and thermal structure from core sample measurements and resistivity log data at Nankai accretionary prism
Leaching of Metals and Metalloids from Hydrothermal Ore Particulates and Their Effects on Marine Phytoplankton
Seafloor
massive sulfide deposits have attracted much interest
as mineral resources. Therefore, the potential environmental impacts
of full-scale mining should be considered. In this study, we focused
on metal and metalloid contamination that could be triggered by accidental
leakage and dispersion of hydrothermal ore particulates from mining
vessels into surface seawater. We determined the leaching potential
of metals and metalloids from four hydrothermal ores collected from
the Okinawa Trough into aerobic seawater and then evaluated the toxic
effects of ore leachates on a phytoplankton species, Skeletonema marinoi–dohrnii complex, which is present ubiquitously in the ocean. Large amounts
of metals and metalloids were released from the ground hydrothermal
ores into seawater within 5 min under aerobic conditions. The main
components of leachates were Zn + Pb, As + Sb, and Zn + Cu, which
were obtained from the Fe–Zn–Pb-rich and Zn–Pb-rich
zero-age, Ba-rich, and Fe-rich ores, respectively. The leachates had
different chemical compositions from those of the ore. The rapid release
and difference in chemical compositions between the leachates and
the ores indicated that substances were not directly dissolved from
the sulfide-binding mineral phase but from labile phases mainly on
the adsorption–desorption interface of the ores under these
conditions. All ore leachates inhibited the growth of S. marinoi–dohrnii complex but with different magnitudes of toxic effects. These results
indicate that the fine particulate matter of hydrothermal ores is
a potential source of toxic contamination that may damage primary
production in the ocean. Therefore, we insist on the necessity for
the prior evaluation of toxic element leachability from mineral ores
into seawater to minimize mining impacts on the surface environment