成岩混层(I/S)Ar-Ar年龄谱型及^(39)Ar核反冲丢失机理研究——以浙江长兴地区P-T界线粘土岩为例

Study on the Ar-Ar Age Spectrum of Diagenetic I/S and the Mechanism of ^(39)Ar Recoil Loss——Examples from the Clay Minerals of P—T Boundary in Changxing, Zhejiang Province

本文以浙江长兴地区P—T界线上的粘土岩为研究对象,对其中的成岩混层I/S进行了K-Ar和Ar-Ar测年实验研究,结果表明,沉积岩中成岩混层I/S的K-Ar年龄在没有碎屑含钾矿物混入的情况下,比其对应的地层时代要年轻。成岩混层I/S的常规40Ar/39Ar阶段升温测年一般情况下得不到年龄坪,只有当类蒙皂石层的含量为零时(即没有膨胀层的成岩伊利石),才能形成平坦的年龄谱。39Ar的核反冲丢失不仅发生在矿物表面,也发生在矿物内部,最高可达48%左右,0.2μm粒级可能是39Ar核反冲丢失量的拐点,同时也表明,用快中子照射硅酸盐样品,核反冲距离可以达到0.2μm。

We dated the diagenetic I/S of P-T boundary in Changxing, Zhejiang Province using K-Ar and ^40Ar/^39Ar method. The results show that. （1） the K-Ar ages of pure diagenetic I/S is younger than the age of the P-T boundary, （2） their ^40Ar/^39Ar age spectrum show staircase-shaped and when the proportion of smectite-like interlayers is zero（pure illite） ,the rate of increase of the ^40Ar^＊/^39Ar is zero, showing flat age spectrum, （3） ^39Ar recoil loss not only exist in the outer part but also in the inner part of the clay minerals and the recoil loss can up to ～48%, and （4） 0. 2μm fraction may be the inflection for the ^39Ar recoil loss and the ^39Ar recoil distance can up to 0. 2μm.