2009 Fiscal Year Final Research Report
Development of stepwise laser spot demagnetization system and itsapplication to planetary geology
| Project/Area Number |
19684017
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| Research Category |
Grant-in-Aid for Young Scientists (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
Geology
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| Research Institution | Tohoku University |
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Principal Investigator |
NAKAMURA Norihiro Tohoku University, 大学院・理学研究科, 助教 (80302248)
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| Project Period (FY) |
2007 – 2009
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| Keywords | 古地磁気 / 局所レーザー消磁 / 隕石 / 先カンブリア代 / 衝撃 / クレーター |
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| Research Abstract |
I have been developing a stepwise laser spot demagnetization system for the application to the micro-paleomagnetic study of pre-Cambrian rocks, shocked crater rocks and meteorites. I employed a Q-switched 30W second harmonic generation Nd : YAG green laser, a digital 2-color pyrometer (300-1000℃) with quartz fiber optics of 600 micrometer and a two-way laser irradiation unit with CCD camera. This laser demagnetization system allows us to stepwisely heat the individual spot area in oriented thin sections. As a sample holder, I developed a X-Y stage controlled vacuum chamber with quartz glass viewport embedded into horizontally-lying 12-folded cylindrical silicon steel. The target sample is hold in a very weak ambient magnetic field of 25nT with 10^<-2>Torr vacuum condition. In addition to laser demagnetization system, I have conducted a micro-paleomagnetic study of shock melt veins in Tenham chondrite and fault gouge samples of Chelungpu fault and Nojima fault, by using a supersonic cutter blade. Through these studies, I found that shock melt veins are a reliable magnetic recorder of ambient field during ancient parent-body collisions, and fault gouge are also a reliable recorder for the earthquake faulting. Although these new techniques of laser demagnetization and micro-paleomagnetic study are powerful, the Pre-Cambrian rocks and meteorites have still suffered metamorphism for a long time scale. Traditional Neel theory of magnetization tells us that single domain magnetic particles relax its remanent magnetization to energetically stable condition in an exponential function of temperature and time. However, it is often that natural magnetization data is not consistent with the theory, being due to metamorphism. To interpret the natural data, I have extended the Neel theory to a stretched exponential function, and derived a new non-linear time-temperature relation for metamorphosed rocks and meteorites.
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[Journal Article] Coarse-grained magnetites in biotite as a possible stable remanence-carrying phase in Vredefort granites2010
Author(s)
N. Nakamura, Okuno, K., Uehara, M., Ozawa, T., Tatsumi-Petrocholis, L., Fuller, M.
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Journal Title
GSA Special Paper "Large Meteorite Impacts and Planetary Evolution IV" (in press)
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[Journal Article] Changes to magnetic minerals caused by frictional heating during the 1999 Taiwan Chi-Chi earthquake2009
Author(s)
Mishima, T., Hirono, T., Nakamura, N., Tanikawa, W., Soh, W., Song, S.R.
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Journal Title
Earth Planets Space 61
Pages: 797-801
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[Journal Article] Characteristics of chlorites in seismogenic fault zones: The Taiwan Chelungpu fault Drilling Project (TCDP) core sample2008
Author(s)
Y.Hashimoto, O.Tadai, M.Tanimizu, W.Tanikawa, T.Hirono, W.Lin, T.Mishima, M.Sakaguchi, W.Soh, S.R.Song, K.Aoike, T.Ishikawa, M.Murayama, K.Fujimoto, T.Fukuchi, M.Ikehara, H.Ito, H.Kikuta, M.Kinoshita, K.Masuda, T.Matsubara, O.Matsubayashi, K.Mizoguchi, N.Nakamura, K.Otsuki, T.Shimamoto, H.Sone, M.Takahashi
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Journal Title
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[Journal Article] Low total and inorganic carbon contents within the Chelungpu fault system.2007
Author(s)
M.Ikehara, T.Hirono, O.Tadai, M., Sakaguchi, N.Nakamura, K.Aoike, K.Fujimoto, Y.Hashimoto, T.Ishikawa, H.Ito, M.Kinoshita, W.Lin, K., Masuda, T.Matsubara, O.Matsubayashi, K.Mizoguchi, M.Murayama, K.Otsuki, H.Sone, M.Takahashi, W.Tanikawa, M.Tanimizu, W.Soh, S.R.Song
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Journal Title
Geochemical Journal v.41
Pages: 391-396
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[Presentation] High remanence intensity of breccia samples: Taiwan Chelungpu-fault Drilling Project (TCDP)2009
Author(s)
Tachibana, S., Nakamura, N., Mishima, T., Hirono, T., Soh, W., Song, S., TCDP team
Organizer
2009 AGU fall meeting
Place of Presentation
San Francisco, USA, Poster
Year and Date
20091214-20091218
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[Presentation] Anomalous Magnetization of Brecciated Samples from the Taiwan Chelungpu-fault Drilling Project (TCDP)2009
Author(s)
Tachibana, S., Nakamura, N., Mishima, T., Hirono, T., Soh, W., Song, S., TCDP team
Organizer
2009 AGU Joint Assembly
Place of Presentation
Toronto, Canada, Poster
Year and Date
20090624-20090627
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[Presentation] Anomalous magnetization of fault gouges recovered from Taiwan Chelungpu-fault Drilling Project (TCDP)2008
Author(s)
Nakamura, N., Uehara, M., Mishima, T., Hirono, T., TCDP team
Organizer
European Geoscience Union General Assembly
Place of Presentation
Vienna, Austria, Oral
Year and Date
20080313-20080318
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