Paleomagnetic Secular Variation for the Last 2 million Years form Young Volcanic Rocks

年轻火山岩过去 200 万年的古地磁长期变化

基本信息

批准号：
01540329
负责人：
TANAKA Hidefumi
金额：
$ 1.34万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

Precise dating of young volcanic rocks by K-Ar method was attempted to offer the basis of detailed paleosecular variation of the geomagnetic field. Samples for dating and paleomagnetic measurements were collected in the Zao Volcanic Group.Most of eighteen andesite lavas and dikes gave reliable radiometric ages, but exceptions are the dike "Roba no Mimi Rock" samples in which the ages of about 1 Ma were reported by the previous studies. Apparently some excess argon trapped in the dike samples is the cause of unsuccessful dating experiment. Review and summary were also given to unpublished age data for five volcano groups in Tohoku Japan obtained from the mass spectrometer of Yamagata University.Andesite lavas and dikes were collected for paleomagnetic study at sixteen sites in Zao Volcano. All samples are stable to AF and thermal demagnetizations, and 16 paleomagnetic directions were successfully determined in which the ages cover from 0.07-1 Ma. Paleointensity experiment by the Coe's version of the Thelliers' method was also made to the most stable 50 specimens selected from eight sites. However, the results were not as successful as the directional data. In spite of fairly high stability of remanence to both AF and thermal demagnetizations, half of the samples showed unreliable behavior in the paleointensity experiments. For one lava flow, Sainokawara lava of 0.21 Ma, two series of experiment were made in different inducing fields of 50 and 20 mT to five specimens in each experiment. Agreements were fairly good between the two sets except for one specimen.Statistical secular variation study was made for paleodirectional data set in Brunhes age including the newly obtained data in this study. The degree of the geomagnetic secular variation was about twice as large as the historical secular variation for the last 400 years.

试图通过K-AR方法对年轻火山岩进行精确约会，以提供详细的古磁场古生物变化的基础。在ZAO火山组中收集了用于约会和古磁测量的样品。十八个安山岩熔岩和堤防中的大多数给出了可靠的辐射年龄，但除前的研究报告了大约1 MA年龄的Dike“ Roba no Mimi Rock”样品。显然，一些被困在堤防样品中的多余氩气是导致约会实验不成功的原因。还对日本东北五个火山群的未发表年龄数据进行了审查和摘要，这些火山是从Yamagata University的质谱仪获得的。在Zao Volcano的16个地点收集了Andesite熔岩和堤防。所有样品均与AF稳定和热电磁化，并成功确定了16个古磁方向，其中年龄覆盖为0.07-1 mA。通过COE版本的Thelliers方法的紫色实验也是从八个站点选择的最稳定的50个标本进行的。但是，结果不如方向数据成功。尽管对AF和热消极的延迟的稳定性相当高，但一半的样品在古显着实验中表现出不可靠的行为。对于一种熔岩流量，在每个实验中，在50和20 mt的不同诱导场上进行了两次实验的sainokawara熔岩。两组之间的协议相当不错。除了一个标本外，在黑发年龄中，包括本研究中新获得的数据（包括新获得的数据）进行了统计的世俗变异研究。地磁世俗变异的程度约为过去400年来历史世俗变化的两倍。