Development of stepwise laser spot demagnetization system and itsapplication to planetary geology

步进式激光光斑退磁系统的研制及其在行星地质中的应用

• 批准号: 19684017
• 负责人: NAKAMURA Norihiro
• 金额: $ 16.31万
• 依托单位: Tohoku University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Young Scientists (A)
• 财政年份: 2007
• 资助国家: 日本
• 起止时间: 2007 至 2009
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-19684017/
• 关键词: 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; 地球電磁気; 地質学; 局所段階レーザー熱消磁; 磁性; 惑星起源・進化; 走査型MI磁場顕微鏡; 衝突溶融脈; 断層破砕帯; クレーター磁気異常; 単結晶斜長石; グリーンレーザー; 局所段階レーザー加熱; 断層古地磁気; フラクタル; 磁化の温度・時間関係

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.

我一直在开发一种分步激光点退磁系统，用于前寒武纪岩石、冲击火山口岩石和陨石的微古地磁研究。采用调Q的30 W倍频Nd：YAG绿色激光器、600 μ m石英光纤数字双色高温计（300-1000℃）和带CCD摄像机的双向激光照射装置。这种激光退磁系统允许我们逐步加热定向薄切片中的单个光斑区域。作为样品保持器，我开发了一个X-Y平台控制的真空室，石英玻璃观察口嵌入水平放置的12折叠圆柱形硅钢。将目标样品保持在具有10 μ Torr真空条件的25 nT的非常弱的环境磁场中<-2>。除了激光退磁系统，我进行了微观古地磁研究的冲击熔融脉Tenham球粒陨石和断层泥样品的车笼埔断层和野岛断层，使用超声切割刀片。通过这些研究发现，震融脉是古母体碰撞时环境磁场的可靠记录，断层泥也是地震断层活动的可靠记录。尽管激光退磁和微古地磁研究等新技术具有强大的功能，但前寒武纪岩石和陨石仍经历了长时间的变质作用。传统的Neel磁化强度理论告诉我们，单畴磁性粒子的剩磁随温度和时间呈指数函数衰减到能量稳定状态。然而，由于变质作用的影响，天然磁化强度数据往往与理论不符。为了解释自然数据，我将Neel理论扩展到一个拉伸指数函数，并推导出一个新的非线性时间-温度关系的变质岩和陨石。

项目成果

Shocked melt veins as recorders of paleomagnetic field for an asteroidal parent-body

冲击熔脉作为小行星母体古磁场的记录器

• 发表时间: 2007
• 作者: Sato;Y. & Nakamura;N.
• 通讯作者: N.

Direct identification of stable remanence carriors: MI magnetic microscopy with demagnetization tests

直接识别稳定剩磁载体：具有退磁测试的 MI 磁显微镜

• 发表时间: 2007
• 作者: Uehara;M & Nakamura;N.
• 通讯作者: N.

Coarse-grained magnetites in biotite as a possible stable remanence-carrying phase in Vredefort granites

黑云母中的粗粒磁铁矿作为 Vredefort 花岗岩中可能的稳定剩磁携带相

• 发表时间: 2010
• 期刊: GSA Special Paper "Large Meteorite Impacts and Planetary Evolution IV" (in press)
• 作者: N. Nakamura;Okuno;K.;Uehara;M.;Ozawa;T.;Tatsumi-Petrocholis;L.;Fuller;M.
• 通讯作者: M.

理科実験の文科系学部開講

文理学院开始教授科学实验

• 发表时间: 2007
• 期刊: 大学の物理教育 v.13
• 作者: 須藤彰三;長谷川琢哉;本堂毅;中村教博;田嶋玄一
• 通讯作者: 田嶋玄一

Anomalous magnetization of fault gouges recovered from Taiwan Chelungpu-fault Drilling Project (TCDP)

台湾车龙埔断层钻探项目（TCDP）发现的断层泥异常磁化强度

• 发表时间: 2008
• 作者: Nakamura;N.;Uehara;M.;Mishima;T.;Hirono;T.;TCDP team
• 通讯作者: TCDP team