Geochemical Journal, Vol. 48 (No. 6), pp. 549-560, 2014
Hisayoshi Yurimoto,1,2* Shoichi Itoh,1 Michael Zolensky,3 Minoru Kusakabe,4 Akiya Karen5 and Robert Bodnar6
1Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan
2Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo 001-0021, Japan
3Astromaterials Research and Exploration Science, KT, NASA Johnson Space Center, Houston, TX 77058, U.S.A.
4Department of Environmental Biology and Chemistry, The University of Toyama, Gofuku 3190, Toyama 930-8555, Japan
5Toray Research Center, Inc., 3-7, Sonoyama 3-chome, Otsu, Shiga 520-8567, Japan
6Department of Geosciences, 4044 Derring Hall, Virginia Tech, Blacksburg, VA 24061 U.S.A.
(Received June 2, 2014; Accepted September 17, 2014)
Determination of isotopic composition of extraterrestrial liquid water provides important information regarding the origin of water on Earth and the terrestrial planets. Fluid inclusions in halite of ordinary chondrites are the only direct samples of extraterrestrial liquid water available for laboratory measurements. We determined H and O isotopic compositions of this water by secondary ion mass spectrometry equipped with a cryogenic apparatus for sample cooling. Isotopic compositions of the fluid inclusion fluids (brines) were highly variable among individual inclusions, -400 < δD < +1300‰; -20 < Δ17O < +30‰, indicating that these aqueous fluids were in isotopic disequilibrium before trapping in halite on asteroids. The isotopic variation of fluids shows that various degrees of water-rock interaction had been underway on the asteroids before trapping between D-rich-16O-poor aqueous fluid, D-poor-16O-rich aqueous fluid, and asteroidal rock by delivery of cometary water onto hydrous asteroids. This may be a fundamental mechanism in the evolution of modern planetary water.
Key words: fluid inclusion, hydrogen isotope, oxygen isotope, asteroid, water