黄河小浪底水库区断层的ESR年龄测定

ESR DATING OF FAULTS IN THE AREA OF XIAOLANGDI RESERVOIR ON THE YELLOW RIVER

为了检验应用ESR方法测定断层运动年龄的可行性,在黄河小浪底水库区内的5个断层剖面上采集了13个样品进行ESR年龄测定。结果指出;研究区内的断层活动大致发生于距今0.154—0.183Ma及0.374—0.532Ma两个时期。并对一些有关问题作了讨论,指出这是一种很有希望的确定断层活动近似年龄的新方法,在地震地质及工程地质领域中具有良好的应用前景。

In order to check the applicability of ESR dating method to determination of the age of fault, 13 samples from fault gouges and calcretes were collected from five fault outcrops in the area of Xiaolangdi Reservoir on the Yellow River. The E' signal of quartz grains from fault gouge, and the signal at g = 2.0000 and g = 2.0036 of calcretes from the loess deposits covered the faults were used for the assessment of AD value.To check the hypothesis that the ESR signal intensity was reset to zero by faulting, pure quartz sand were pressed to 17 kbar in a vessel. The result shows that the E' signal intensity was decreased to 24 % of the original intensity. In addition, the AD value of the sample collected from the sliding face of the fault was decreased greatly compared with the sample collected from the normal position located five metres away from the fault zone. It indicates that the zeroing effect of faulting seems to have occurred but the ESR signal intensity was not completely reset to zero. The ESR age therefore, is considered to be a rough estimation of the period of fault movement.The measurement of samples from fault outcrops resulted in ages ranging from 0.154-0.532 Ma for the fault gouges and 0.098-0.348 Ma for the calcretes from the loess deposits covered the faults. It is in accordance with their relative chronology estimated from the geological field evidence. The determination indicates that the ESR method is a promising technique for determining approximate age of fault movement.