自然演化碎屑锆石裂变径迹长度影响因素分析

Influence Factors of the Fission-track Length in Detrital Zircon Obtained from Natural Borehole Samples

锆石裂变径迹长度是锆石裂变径迹热年代学研究的一个重要参数。基于不同热背景的沉积盆地样品实测数据,分析锆石裂变径迹的退火行为,探讨锆石裂变径迹长度的影响因素。研究表明,Sk1井样品的裂变径迹长度和径迹与结晶C轴夹角之间具有一定的负相关性,即夹角愈小,径迹长度愈长;反之,夹角愈大,径迹长度愈短。Sk1井样品径迹与结晶C轴夹角主要分布在10°~70°,整体分布较随机;而Ku1井样品多分布于高角度(60°~90°),整体分布不随机。Sk1井锆石裂变径迹在沉积盆地开始退火温度为220℃,深层样品的平均径迹长度为5.02~5.55μm;Ku1井锆石裂变径迹在沉积盆地开始退火温度为170℃,深层样品的平均径迹长度为8.06~8.31μm,高温热背景下Sk1井的锆石裂变径迹开始受到沉积盆地影响的温度高于Ku1井。研究认为锆石裂变径迹在不同热背景下的开始退火温度和退火行为产生的差异是由盆地不同的增温速率导致的。Sk1井的中浅层样品平均径迹长度范围为5.85~8.36μm,Ku1井中浅层样品平均径迹长度为9.21~10.05μm。2口井中浅层样品的最小年龄大于地层年龄,表明未受到沉积盆地的影响,缩短的径迹长度是受到母源区热事件的影响。对锆石裂变径迹的退火行为和径迹长度影响因素的分析对于油气成藏过程以及烃源岩的热演化史研究具有指导意义。

Zircon fission-track length is an essential parameter for studying annealing behavior.Based on measured data from sedimentary basin samples with different thermal backgrounds,this study investigated the annealing behavior of zircon fission tracks and discussed the factors influencing the fission-track length.The results show that the fission track of the Sk1 sample has a negative correlation with the angle to the C-axis on the fission track;specifically,a smaller angle corresponds to a longer track length,while a larger angle results in a shorter track length.The angle to the C-axis on the fission-track of the Sk1 sample was mainly distributed at 10°~70°,and the overall distribution was relatively random.The Ku1 samples were primarily distributed at high angles(60°~90°),and the overall distribution was not random.The initial annealing temperature of zircon fissions track in the sedimentary basin of Sk1 is 220℃,and the average track length of deep samples is 5.02~5.55μm.The initial annealing temperature of the zircon fission track in the sedimentary basin of Ku1 is 170℃,and the average track length of deep samples is 8.06~8.31μm.Under a high temperature and thermal background,the temperature at which the zircon fission track of Well Sk1 was affected by the sedimentary basin was higher than that of Well Ku1.The difference in initial annealing temperature and annealing behavior of zircon fission tracks with different thermal backgrounds is attributed to variations in the heating rate.The average track length of the middle and shallow samples in well Sk1 is 5.85~8.36μm;the average track length in the Ku1 well is 9.21~10.05μm.The minimum age of shallow samples in both wells exceeded the formation age,indicating that they were not affected by the sedimentary basin.Instead,the shortened track length was affected by thermal events in the source.