Japan Geoscience Union Meeting 2016

Presentation information


Symbol S (Solid Earth Sciences) » S-GL Geology

[S-GL38] Geochronology and Isotope Geology

Tue. May 24, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Takahiro Tagami(Graduate School of Science, Kyoto University), Yuji Sano(Division of Ocean and Earth Systems, Atmosphere and Ocean Research Institute, University of Tokyo)

5:15 PM - 6:30 PM

[SGL38-P03] Argon Isotopic Composition on Mauna Loa Historical Lavas

*Ruri Kawamura1, Keiko Sato2, Hidenori Kumagai2, Takeshi Hanyu2, Katsuhiko Suzuki2, Takahiro Tagami1 (1.Department of Geology and Mineralogy, Division of Earth and Planetary Sciences, Graduated School of Science, Kyoto University, 2.Japan Agency for Marine-Earth Science and Technology)

Keywords:K-Ar method, mass fractionation, Mauna Loa volcano

K-Ar and Ar-Ar dating are widely adopted method to the reconstructions for the eruption history of the active volcanoes. Regardless of the wide use, there is a fatal problem of its basis that the initial argon isotope ratios are not fully reset, in other words, incompletely equilibrated with the atmospheric Ar. Although this phenomenon has been occasionally reported, the factors controlling have not intensively been investigated yet. Thus in this study, a set of lava systematically sampled from a historical lava flow was analyzed: sixteen samples from 1935 lava flow on Mt. Mauna Loa. Ar isotope measurement was performed with GVI-5400He as well as their major element compositions with XRF (Simultix12, Rigaku Co.) at JAMSTEC. Most of the samples showed smaller 38Ar/36Ar compared with the atmospheric isotope ratio. It may be a result of some magmatic processes at depth as well as shallower eruption related ones. Regardless of an anticipated enrichment of heavier isotopes that correlates with vesicularity for the residual argon in vesiculation, all the samples showed enrichment of lighter isotopes. Further, there is no clear correlation with vesicularity, lava type nor distances from the vent of the flow, etc.