GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 23-18
Presentation Time: 9:00 AM-5:30 PM


ISHIBASHI, Junichiro1, TSUKAMOTO, Naru1, NAKAI, Shun'ichi2, FUJIWARA, Taisei3, OBATA, Naoya3, GOTO, Takashi3, GOUZU, Chitaro3, UCHIDA, Ai4 and TOYODA, Shin4, (1)Department of Earth and Planetary Sciences, Kyushu University, 744 Motooka Nishi-ku, Fukuoka, 8190395, Japan, (2)Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi Bunkyo-ku, Tokyo, 1130032, Japan, (3)Hiruzen Institute for Geology and Chronology, 2-5 Nakashima Naka-ku, Okayama, 7038252, Japan, (4)Applied Physics, Okayama University of Science, 1-1 Ridai Kita-ku, Okayama, 7000005, Japan

Chronological studies of hydrothermal mineral deposits are useful, because accumulation of metal elements to be "resource" requires duration and evolution of mineralization processes in a time scale of 103 to 105 years. Since 1980s, several dating studies have been applied to sulfide and sulfate deposits collected from seafloor hydrothermal fields. For geochronological studies of these mineral deposits, there is an important pending problem when the system is closed, because hydrothermal deposits are likely to grow up by repeated mineralization. To overcome this problem, we tried to yield practical applications of trapped charge dating techniques. We conducted electron spin resonance dating of sulfate deposits and thermoluminescence dating of siliceous sediment, and compared results of these dating techniques with those obtained by radiometric dating techniques such as 234U-230Th disequilibrium method for sulfide minerals, and 226Ra-210Pb and 228Ra-228Th disequilibrium methods for sulfate minerals. Our main study field is hydrothermal fields in the Okinawa Trough, where modern analogue of Kuroko-type volcanogenic massive sulfide deposits have been located. Mineralization of these hydrothermal deposits are characterized by coexisting occurrence of polymetallic sulfide minerals and abundant sulfate minerals. Preliminary studies revealed that the obtained ages from hydrothermal fields with large hydrothermal deposits range from several years to several thousand years. Our ongoing program is dating of sediment core samples obtained by scientific drillings within and around active hydrothermal fields. The chronological studies are expected to provide important constraints to understand formation mechanisms of seafloor massive sulfide deposits.