@article{oai:repo.qst.go.jp:00058538,
 author = {Ishibashi, Jun-ichiro and Shimada, Kazuhiko and Sato, Fumihiro and Uchida, Ai and Shin, Toyoda and Takamasa, Asako and Shun’ichi, Nakai and Hyodo, Hironobu and Sato, Keiko and Kumagai, Hidenori and 賞雅 朝子},
 journal = {Subseafloor Biosphere Linked to Hydrothermal Systems},
 month = {Jan},
 note = {Ages of sulfide and sulfate mineralized samples collected from active hydrothermal fields
in the Southern Mariana Trough were determined. In addition to samples collected from
active and inactive chimneys, and sulfide breccia during dive expeditions, massive sulfide
ores obtained by shallow drilling were studied. We applied 230Th/234U radioactive disequilibrium
dating technique to sulfide minerals, as the collected mineralized samples were
dominated by marcasite, pyrite and sphalerite. In addition, electron spin resonance (ESR)
dating was applied to a few barite-rich samples, for comparison purpose. A laser step
heating 39Ar-40Ar dating of the basement volcanic rock samples was also attempted.
Sulfide chimneys and ores collected from a hydrothermal mound located beside the
spreading axis range in age from <100 to 3,520 years old, without notable hiatus. The
growth rate of the massive sulfide ore body is calculated to be 0.12–1.5 mm year 1 based on
results of the core samples. This age range is comparable for those previously reported for
giant hydrothermal mounds of a few 100 m in diameter. These results suggest >1,000 years
of continuous hydrothermal activity would be necessary for the formation of a massive
sulfide deposit.
Sulfide chimneys and breccia collected from two hydrothermal fields located on an offaxis
knoll are up to 9,000 years old. Sulfide breccia collected from an active site on the
spreading axis are 2,740 and 7,190 years old. Geophysical studies provided evidence for
abundant magma supply in the Southern Mariana Trough, which would have fueled
hydrothermal activities in this area for long duration. While geophysical evidence for
crustal velocity anomaly below the off-axis knoll suggests mineralization at the off-axis
sites is considered to be in the late-stage of the hydrothermal activity, the discrete ages from
the on-axis site might reflect episodic hydrothermal activities related to diking events
proposed by geophysical and geological studies.},
 pages = {289--300},
 title = {Dating of Hydrothermal Mineralization in Active Hydrothermal Fields in the Southern Mariana Trough},
 year = {2015}
}