Japan Geoscience Union Meeting 2015

Presentation information


Symbol S (Solid Earth Sciences) » S-GC Geochemistry

[S-GC51] Frontiers in noble gas isotope geosciences

Sun. May 24, 2015 6:15 PM - 7:30 PM Convention Hall (2F)

Convener:*Hironobu Hyodo(Research Institute of Natural Sciences, Okayama University of Science), Hirochika Sumino(Geochemical Research Center, Graduate School of Science, University of Tokyo), Takahiro Tagami(Graduate School of Science, Kyoto University)

6:15 PM - 7:30 PM

[SGC51-P05] Possibility of K-Ar age mapping on the moon using cosmogenic ^{39}Ar

Yuko TAKESHIMA1, *Hironobu HYODO2, Tetsumaru ITAYA2 (1.NEC Aerospace systems, 2.RINS, Okayama Univ. of Sci.)

Keywords:^{39}Ar, Cosmogenic, age distribution, ^{40}Ar/^{39}Ar age, moon surface

Rapid and wide range of age survey on the moon surface requires in situ measurement. 39Ar of cosmogenic origin from 39K in meteorite has been noticed since the early stage of noble gas research, and became a cue to the 40Ar/39Ar method. If the production rate of 39Ar is considered uniform, the production and decay of 39Ar reaches to equilibrium after a long time, since 39Ar has a half life of 293 years. This half life is long enough to detect 39Ar in meteorites and moon rocks, and short enough to reach equilibrium of the isotope. Thus, such rocks or minerals possess a certain amount of 39Ar proportional to their potassium content. Using meteorites or rocks on moon surface under the same exposure condition, 40Ar/39Ar age can be determined. For a start, a precise date of one of those samples in a laboratory and 40Ar/39Ar ratio measurement of the same sample in the field are required to obtain J-value in the field. 40Ar/39Ar ratios measurement of the rest of unknowns in the field allow us to calculate ages. Interfering isotopes from calcium will not affect much as long as Ca/K ratio is low. Samples in a depth or a shadow from exposure are not suitable for the measurement since the neutron density attenuates with depth. However, no need for atmospheric contamination, mass measurement and 36Ar measurement may provide us more mobility and rapid measurement.