闪锌矿铷-锶同位素等时线讨论

A Discussion of Sphalerite Rb-Sr Isotopic Isochron

通过对闪锌矿铷-锶同位素等时线形成机制的讨论,若为同源、同期、待测同位素封闭的体系,因混合形成的直线为等时线具有定年意义,但若非同源、非同期或非封闭的体系亦可因混合形成直线,但该直线为无年代学意义的混合线。作为铷-锶同位素定年矿物,闪锌矿可能仅充当"容器"的角色,因此利用闪锌矿进行定年时,必须进行细致的物相研究。闪锌矿中的碳酸盐、硅酸盐等矿物微粒可能对铷-锶定年产生极大的影响,如不能对其进行成因鉴别或配合其他同位素定年方法加以系统研究,闪锌矿铷-锶法直线拟合结果很难反映成矿时间。

By discussing genesis of sphalerite Rb-Sr isochron, it can be pointed that the mixing line produced by the tested isotopes system, which is cogenetic, syngenetic and closed, brings the geological age. The system related to tested isotopes, however, which may be no cogenetic, syngenetic or closed, also brings ＂isochron＂ —— a meaningless mixing line. Sphalerite, the object of isotope dating, maybe just play the role of ＂container＂, while mineral particulates such as carbonate, silicate etc. produce remarkable influence to the analyses, so a elaborate mineralogical work is indispensable before isotopes analyses carrying on. So the isochron is bad to reflect the geological fact if these particulates are not discussed on genesis or the dating object has not been tested on other isotopic chronological methods.