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ESR/ICP-MS dating method of the latest fault movement

最新断层运动的ESR/ICP-MS测年方法

基本信息

批准号：
10640441
负责人：
FUKUCHI Tatsuro
金额：
$ 2.11万
依托单位：
Yamaguchi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10640441/
关键词：
fault gouge Nojima Fault electron spin resonance ICP-MS radon anomaly Nojima Fault-zone probe α-ray neutron 野島断層 ESR ICP-MS 粘土鉱物摩擦熱兵庫県南部地震

项目摘要

First, we inspected the resetting state of ESR signals using the Nojima Fault 500m drilling core samples, and confirmed that ESR signals in the fault gouge had been thermally reduced. This means that fault gouge samples as deep as possible are necessary for complete resetting of ESR signals. As a result of computer simulation on the decay process of ESR signals in the fault gouge, it was found that we should consider as a resetting mechanism not only frictional heat but also vaporization or convection of pore and crystal water in the fault gouge.Next, we carried out chemical analysis of the fault gouge in the 500m core samples to confirm whether or not Pb anomaly actually exists. We analyzed by ICP-MS 8-20 μ m fractions separated from the bulk samples of the fault gouge. As a result we detected extreme ィイD1208ィエD1Pb/ィイD1232ィエD1Th and ィイD1206ィエD1Pb/ィイD1238ィエD1U ratio anomalies from the 0-3mm part just on the fault plane. In the 0-3mm and 3-6mm parts of the fault gouge, the intensity of ィイD1206ィエD1Pb/ィイD1238ィエD1U ratio is larger than that of ィイD1208ィエD1Pb/ィイD1232ィエD1Th ratio, whereas in the parts of more than 6mm away from the fault plane, the intensity of ィイD1206ィエD1Pb/ィイD1238ィエD1U ratio is smaller than that of ィイD1208ィエD1Pb/ィイD1232ィエD1Th ratio. This suggests that the Pb anomaly may not be derived from the migration of the whole Pb isotopes, but from that of apart of ィイD1206ィエD1Pb or ィイD1208ィエD1Pb. The Pb anomaly may be explained by the existence of Rn anomaly.Furthermore we experimentally generated fault gouge by hyirothermal reaction at high temperature and confirmed that smectites are easily generated in natural. One can evaluate fault activity by ESR dating of fault gouge using an intrinsic ESR signal in smectites. In addition, we found by high energy particles irradiation a new ESR signal in quartz, which is applicable to ESR dating.

首先，我们使用野岛断层500米钻孔岩心样品检查了ESR信号的复位状态，并确认了断层泥中的ESR信号已被热还原。这就意味着，要使ESR信号完全复位，就必须采集尽可能深的断层泥样品。通过对断层泥ESR信号衰减过程的计算机模拟，发现断层泥中不仅存在摩擦热，而且存在孔隙水和结晶水的蒸发或对流，这是一种重置机制。用ICP-MS分析了断层泥中8-20 μ m的组分。在断层面0- 3 mm处，测得D1208-Pb/D1232-Th和D1206-Pb/D1238-U比值异常。在断层泥0- 3 mm和3- 6 mm处，断层泥D1206 Pb/Pb/D1238 Th比值的强度大于D1208 Pb/Th比值的强度，而在距断层面6 mm以上的部分，铀D1206的D1 Pb/铀D1238的D1 U比值小于铀D1208的D1 Pb/铀D1232的D1 Th比值。这表明铅异常可能不是由全铅同位素的迁移引起的，而是由部分铅同位素的迁移引起的。Pb异常可以用Rn异常的存在来解释。此外，我们还通过实验研究了断层泥在高温下的热液反应，证实了蒙皂石在自然界中很容易生成。人们可以利用蒙脱石中固有的ESR信号，通过断层泥的ESR测年来评估断层的活动性。此外，我们还发现了一种新的ESR信号，可用于石英的ESR测年。