Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Poster

B (Biogeosciences) » B-BG Biogeosciences & Geosphere-Biosphere Interactions

[B-BG02] Interrelation between Life, Water, Mineral, and Atmosphere

Mon. May 21, 2018 1:45 PM - 3:15 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Ken Takai(Extremobiosphere Research Center, Japan Agency for Marine-Earth Science & Technology), Kentaro Nakamura(Department of Systems Innovation, School of Engineering, University of Tokyo), Yuichiro Ueno(東京工業大学大学院地球惑星科学専攻, 共同), Yohey Suzuki(Graduate School of Science, The University of Tokyo)

[BBG02-P09] 230Th ages of brucite-carbonate chimneys at the Shinkai Seep Field, southern Mariana forearc

*Tomoyo Okumura1, Chuan-Chou Shen2, Marjoor Ahmad Lone2, Tsai-Luen Yu2, Akihiro Kano3, Amekawa Shota3, Taiki Mori4, Yasuhiko Ohara5,6 (1.Center for Advanced Marine Core Research, Kochi University, 2. High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, 3.Department of Earth and Planetary Science, The University of Tokyo, 4.Graduate school of integrated science for global society, 5.Hydrographic and Oceanographic Department of Japan, 6.Department of Subsurface Geobiological Analysis and Research, Japan Agency for Marine-Earth Science and Technology)

Keywords:serpentinization, alkaline fluid, brucite-carbonate chimney

Serpentinite-hosted fluid vent systems have attracted interest as analogues for the place of birth of life on the Earth as well of extraterrestrial life expected on Mars and Enceladus. During the past five-years expeditions, brucite-carbonate chimneys were discovered from the deepest known (~5700 m depth) serpentinite-hosted ecosystem, the Shinkai Seep Field (SSF) in the southern Mariana forearc [1]. Previous study for the chimney textures and mineralogies recognized two types (type I and II) of active chimneys formed under compensation of the precipitation and dissolution of constituent minerals [2]. Type I chimneys are mainly consist of brucite; these formed as a result of rapid precipitation under high discharge of alkaline fluid. In this type of chimneys, filamentous microbial cells were often mineralized by brucite. Type II chimneys are characterized by inner brucite-rich and outer carbonate rich zones and were likely formed under lower fluid discharge than the type I chimneys. Type II chimneys are covered with non-lithified grayish microbial mats and colonies of Phyllochaetorterus. In this study, we applied uranium-thorium disequilibrium dating for the two types of chimneys to elucidate the history of the chimney growth.
Ages of the type I chimneys ranged from modern to 14,000 yrs and its median age was 350 yrs. The type II chimneys showed older age than that of type I, which ranged from 1,600 to 18,000 yrs with 6,000 yrs median age. These results indicated that the intensity of fluid discharges also controlled growth rate of the brucite-carbonate chimneys. The broad age ranges likely resulted from the compensation of mineral precipitation and dissolution occurring below the local carbonate compensation depth. Such conditions provides a habitat for microbes and animals for >10,000 yrs on deepsea floor, which are encased in mineral precipitates.

[1] Ohara et al. (2012) Proc. Natl. Acad. Sci. U. S. A., 109, 2831–2835.
[2] Okumura et al. (2016) Geochem. Geophys. Geosys. 17, 3775–3796.