江汉平原地下水混合的^(14)C年龄曲线投影校正研究

A study on the curvilinear projection clibration of mixed^(14)C ages for groundwaters in Jianghan Plain

地下水^(14)C年龄的分布可以指示地下水渗流的方向及其变化。经典校正模型可以消除水化学组成变化对^(14)C年龄的影响,但很难识别地下水混合,导致得到的^(14)C年龄代表的是地下水的混合年龄。本文根据地下水化学组分变化提出了识别混合和校正a^(14)C值的方法,并以江汉平原为研究实例进行解剖。江汉平原地下水中硫酸盐矿物溶解导致SO_(4)^(2-)含量增加,且SO_(4)^(2-)含量与a^(14)C值的关系曲线可以识别混合,并利用曲线投影校正a^(14)C值,提出了混合-IAEA模型。IAEA年龄和混合-IAEA年龄的分布差异揭示出地下水渗流变化。年轻地下水混合区为年轻地下水的汇聚方向;老地下水混合区为老地下水的汇集方向。因此,对于大型沉积平原(或盆地)的地下水流系统,使用^(14)C定年时需要考虑地下水混合的影响,混合校正后的^(14)C年龄可以用来识别地下水渗流变化。

The distribution of^(14)C ages of groundwaters can indicate the direction and its change of groundwater seepage.The classical calibration models can eliminate the impact of^(14)C ages by changes of hydrochemical compositions of groundwaters,but hardly identify the mixing of groundwaters,resulting in that the obtained^(14)C ages represent mixed ages of groundwaters.In this paper,we have proposed a method for identifying the mixing of groundwaters and calibrating a^(14)C values of groundwaters based on changes of hydrochemical compositions of groundwater samples along the flow path of groundwater,and have undertaken a case study of the groundwaters in the Jianghan Plain.The dissolution of sulfate minerals in groundwaters in the Jianghan Plain leads to the increase of SO_(4)^(2-)contents in groundwaters.The relationship curve between SO_(4)^(2-)contents and a^(14)C values of groundwaters can be used to identify the mixing of groundwaters and to calibrate a^(14)C values of groundwaters by using the curvilinear projection.Thus,we have proposed the mixed-IAEA model.The difference between the IAEA modelling age and the mixed-IAEA modelling age can be used to reveal the change of groundwater seepage.The mixing area of young aged groundwaters repersents the convergence direction of groundwaters in the Jianghan Plain,while the mixing area of old aged groundwaters represents the the convergence direction of the old aged groundwaters.Therefore,it is necessary to consider the influence on^(14)C dated ages of groundwaters by the mixing of grounderwaters for the groundwater flow system in large sedimentary plains(or basins).The calibrated^(14)C ages by using the mixed-IAEA model can be used to identify the change of groundwater seepage.