Japan Geoscience Union Meeting 2015

Presentation information

Oral

Symbol M (Multidisciplinary and Interdisciplinary) » M-TT Technology & Techniques

[M-TT44] Frontiers in Geochemistry: Prospect for geochemistry in 30 years

Tue. May 26, 2015 4:15 PM - 6:00 PM 102B (1F)

Convener:*Takafumi Hirata(Graduate School of Science, Kyoto University), Yoshio Takahashi(Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo), Urumu Tsunogai(Graduate School of Environmental Studies, Nagoya University), Hajime Obata(Marine inorganic chemistry division, Atmosphere and Ocean Research Institute, University of Tokyo), Shogo Tachibana(Department of Natural History Scieces, Hokkaido University), Katsuhiko Suzuki(Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology), Gen Shimoda(Geological Survey of Japan, AIST), Hiroyuki Kagi(Geochemical Laboratory, Graduate School of Science, University of Tokyo), Yusuke Yokoyama(Atmosphere and Ocean Research Institute, University of Tokyo), Tetsuya Yokoyama(Department of Earth and Planetary Sciences, Graduate School of Science and Engineering, Tokyo Institute of Technology), Chair:Takafumi Hirata(Graduate School of Science, Kyoto University), Yoshio Takahashi(Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo)

5:45 PM - 6:00 PM

[MTT44-09] Molecular Geochemistry as a Future Topic in Geochemistry

*Yoshio TAKAHASHI1 (1.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo)

Keywords:Molecular Geochemistry, Goldschmidt

Professor V. M. Goldschmidt is a father of geochemistry. He wrote in 1954 that geochemistry is the study of the distribution and amounts of the chemical elements in minerals, rocks, soils, water, and the atmosphere, and the study of the circulation of the elements in nature, on the basis of the properties of their atoms and ions. Based on this concept, he discussed (i) substitution of trace elements into major element within a certain crystal, (ii) reaction of metal ions with the ligands in water in terms of ion potential (= z/r; z: charge; r: ionic radius), and (iii) classification of all the elements in the periodic table in terms of chemical bounding nature such as ionic, covalent, and metallic bonding. Using X-ray emission spectroscopy, which was the state-of-the art method at that time, he determined abundances of trace elements in various geochemical samples.

However, his discussion on the distribution of these elements on the basis of the properties of their atoms and ions could not be proved by any methods, since it was difficult at that time to clarify the chemical species (bonding nature and structure) of trace elements. At present, on the other hand, we can determine the neighboring atom and interatomic distance of trace elements in various samples by advanced speciation methods such as by X-ray absorption fine structure (XAFS) spectroscopy. As shown in our recent studies, abundances and isotopic compositions of various elements in natural samples strongly depend on the chemical state of various elements in nature. This fact shows that we can predict behaviors and isotopic fractionation of various elements based on physic-chemical properties. This field can be called as "Molecular Geochemistry". This field includes (i) identification of organic polymolecules in nature which can be used for the paleoenvironment reconstruction, (ii) isotopomers of various molecules, and (iii) fundamental understanding of isotopic fractionation such as mass-independent fractioation. Thus, I propose "Molecular Geochemistry" as an important future topic of geochemistry, which cannot be conducted by researchers in other fields in earth and planetary sciences and must be conducted by Prof. Goldschmidt if he could use the methods to reveal the atomic- and molecular-level information in geochemical samples.