用于同位素测年的自生伊利石分离纯化流程探索

The Separation of Authigenic Illite from Detrital Illite in Sedimentary Rock for Ar Isotope Dating

沉积岩中自生矿物与碎屑矿物的分离问题是制约沉积岩定年的主要问题之一。本文以浙江和川西地区的粘土矿物为例 ,介绍了沉积岩中自生伊利石与碎屑矿物的一般分离过程 ,具体包括悬浮液的制备过程、高速离心机的条件实验和 8个样品的分级实验 ,确定了较佳的分级参数 ,并对分级后的各级别进行了X 射线衍射 (XRD)分析。X 射线衍射结果表明 ,随着粒度的减小 ,各种杂质的含量都在逐渐减少 ,在小于 0 .2 μm的粒级中 ,已检测不出石英、钾长石、钠长石、方解石、白云石等杂质的存在 ,其中有 3个产品的成岩混层含量达到 10 0 % ,,说明本次实验的分离纯化流程是比较成功的。综合考虑粒度和自生伊利石的纯度 ,一般情况下 ,以 0 .1～ 0 .2 μm粒级的产品用于Ar Ar和K Ar测年较合适。但在实际进行年龄分析时 ,一定要先进行XRD和透射电镜分析 ,只有确定其成岩混层I/S的含量近 10 0 % (至少在 95 %以上 )及混层中S的含量小于 2 5 %时 ,才可用于Ar Ar和K

The dating of sedimentary rock has in part been hampered by the problem of complete separation of authigenic illite from detrital illite. Taking the clay minerals of Changxing area in Zhejiang Province as an example, this paper describes the separation procedure of authigenic illite from detrital illite, with all the grain size fractions analyzed by X-ray diffraction (XRD). The result shows that impurities such as quartz, potassium feldspar, albite, calcite and dolomite decrease gradually with the reduction of grain size, and there are no detectable impurities in the <0.2 μm fraction. It is especially striking that the content of mixing I/S in the samples 5-4,6-3 and 6-4 is 100%, which shows that the separation is relatively successful.