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近年来碳酸盐岩石Pb-Pb和U-Pb地质年代学的应用,对原生沉积作用(严格说是早期成岩作用)和沉积变质作用的年龄测定做出了重要贡献。本文总结了这方面的显著发展,讨论了碳酸盐岩石U-Pb和Pb-Pb计时器的功能,概括其主要优缺点和未来要解决的一些问题。 像所有经典测年方法(Rb-Sr、K-Ar、Sm-Nd和锆石U-Pb)一样,未变质碳酸盐U-Pb和Pb-Pb年龄的真实性,依赖于U-Pb系统之封闭性。仅有碳酸盐的U-Pb或Pb-Pb年龄不能赋予确切的地质意义。然而,对于变质碳酸盐来说,大理岩的Pb-Pb等时线年龄则一般是准确地反映变质重结晶作用时间。应用Wendt(1984)三维研究方法可 以增加获得有关碳酸盐热历史和U-Pb分馏作用信息。 来自16个地方,从大古代到中生代有价值的碳酸盐年龄数据显示,除一个例外(穆尚迪凯灰岩),全部模式μ1值变化很小,为8.4±0.4。与封闭系统同位素均一化预计的不一样,从来没有观测到变质碳酸盐有非常高的μ1值,表明(1)成岩或变质作用条件下,Pb是在一个包含有碳酸盐Fb和外来Fb的开放系统中被均一化,(2)外来Pb具有主要大陆储、库的特征,而这个储库控制着均一化后碳酸盐U-Fb系统中的Fb聚集。 至今已发表的U-Pb和Pb-Pb年龄还不足以用来精确地标定显生宙地质年表。尽管用U-Pb法和Ph-Fb法已成功地测定了相当多碳酸盐?
The application of Pb-Pb and U-Pb geochronology to carbonate rocks in recent years has made an important contribution to the age determination of primary sedimentation (strictly speaking, early diagenesis) and sedimentary metamorphism. This article summarizes the remarkable developments in this area, discusses the function of carbonate rock U-Pb and Pb-Pb timers, summarizes their main advantages and disadvantages, and some problems to be solved in the future. As with all classical dating methods (Rb-Sr, K-Ar, Sm-Nd and zircon U-Pb), the authenticity of U-Pb and Pb-Pb ages of uncalcined carbonate depends on the U-Pb system Closed. The carbonate-only U-Pb or Pb-Pb age can not give the exact geological meaning. However, for metamorphic carbonates, the Pb-Pb isochron age of marble generally reflects exactly the duration of metamorphic recrystallization. Using Wendt’s (1984) three-dimensional research approach can add information about the thermal history of carbonate and U-Pb fractionation. Data from 16 places, from the ancient to the Mesozoic valuable carbonate age data, show that with all but one exception (the Muchandikay limestones), the μ1 values for all modes vary very little at 8.4 ± 0.4. Unlike the predicted homogeneity of the closed system isotopes, a very high μ1 value for metamorphic carbonate has never been observed, suggesting that (1) Pb is formed during a diagenetic or metamorphic process in a solution containing carbonate Fb and exogenous Fb (2) Exogenous Pb has the characteristics of a major continental reservoir, and this reservoir controls the Fb accumulation in the homogenized carbonate U-Fb system. U-Pb and Pb-Pb ages so far published are not enough to accurately calibrate the Phanerozoic geochronology. Although quite a bit of carbonate has been successfully measured using U-Pb and Ph-Fb methods?