Japan Geoscience Union Meeting 2014

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Oral

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

[S-GL42_29AM2] Geochronology and Isotope Geology

Tue. Apr 29, 2014 11:00 AM - 12:45 PM 419 (4F)

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

12:25 PM - 12:40 PM

[SGL42-P03_PG] Diffusion experiment by stepwise heating and muscovite

3-min talk in an oral session

*Hironobu HYODO1 (1.RINS, Okayama Univ. of Sci.)

Keywords:diffusion experiment, argon, closure temperature, stepwise heating, muscovite

It is generally recognized that diffusion experiment on micas in vacuum during stepwise heating for 40Ar/39Ar dating was unsuitable for diffusion studies because of the destruction of crystal structure from dehydration. However, we showed that estimates of closure temperature from single grain biotites during laser heating experiment gives reasonable values. The problem in case of muscovite is that it seems to have structural transition or significant destruction between 600 and 700oC. The recent study using hydrothermal environment reported the activation energy E of 63 kcal/mole and an estimation of closure temperature exceeding 400oC. The high E and closure temperature Tc are derived on the steep slope in Arrhenius plot. Without change in crystal structure, muscovite does not give high E and Tc. This is contradictory for samples with high E and Tc. It is necessary to separate diffusion phenomena from structural change, and even a hydrothermal experiment at high temperatures in a laboratory may not be suitable for such studies. Muscovite is known to have relatively high Tc in field. To make a practical estimate for Tc, it is necessary to consider both laboratory and field setting.