断层电子自旋共振定年中石英信号强度的影响因素分析

电子自旋共振(ESR)是一种利用矿物在地质环境中的累计辐射能进行测年的技术方法,它采用的测年矿物石英广泛分布,并具有记录断层作用良好的计时零点,是同位素测年的重要补充。ESR信号强度是决定ESR年龄精确度的关键因素,但是各种参数条件对测量结果的影响方式及其程度缺乏系统研究。本文以取自断层带石英的一种顺磁中心——E’心为研究对象,运用单因素重复性实验方法,分析石英ESR定年中5种影响因素与ESR信号强度的相关关系。结果表明,微波功率、调制幅度、扫描宽度是影响ESR信号强度的主控因素,样品管方位及直径对测量结果影响不大。微波功率0.02~0.1 m W、调制幅度0.25~0.4 Gs可作为精确测量断层泥石英E’心普适性的参数区间,过大或过小的扫描宽度均不利于ESR测量,可利用在大扫描宽度条件下先预扫描再精细扫描的方法确定合适的扫描宽度,重复测量后求取平均值可有效降低测量误差。利用本文提出的参数区间及其确定的方法测量断层泥石英的E’心信号强度,能显著提高ESR测量精度。

The Analysis of Influence Factors on Electron Spin Resonance Signal Intensity in Dating of Quartz in Fault Lines

Electron Spin Resonance (ESR) is a dating technique using the accumulated irradiation energy in minerals under geological environments as the target. The quartz used for isotopic dating is widely distributed, and has an excellent time starting point to record fault deformation. This implies that ESR will become a valuable supplement to isotopic dating. ESR signal intensity is the key factor affecting the accuracy of ESR age, but the influence pattern and degree of different parameters on ESR signal intensity remains unknown. A paramagnetic E'' center in quartz from fault zones was taken as the main investigation object. By single factor repeated experimental method, the relationship between 5 parameters of ESR dating and ESR signal intensity was analyzed. The results indicate that microwave power, field modulation amplitude, and scan width are the most important factors affecting ESR signal intensity, however the inserted direction and diameter of the sample tube had a slight influence on measuring the data. The microwave power from 0.02 mW to 0.1 mW (in Fig.1), and the field modulation amplitude from 0.25 Gs to 0.4 Gs can be used as a universal parameter range to precisely measure E'' center in fault clay quartz (in Fig.3). Improper scan width was unsuitable for ESR measuring. Before the fine scanning, the pre-scan should be performed under wider scan width and then the proper scan width can be identified. Calculating the average value based on repeated measuring data can help to decrease measurement error effectively. When the proposed parameter range and measuring method are used to measure the E'' center signal intensity of fault clay quartz, the ESR measurement precision can be improved remarkably.