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The various methods of geochronology have, as a rule, evolved along a characteristic path whereby the earliest work lays out the physical and mathematical foundation and demonstrates its practicality for a few cases using optimal samples. Later work confronts the problems and failures of early assumptions on more general problems, and as the method matures and becomes more generally applied, a standard toolkit of more-or-less rigorous protocols for data interpretation and error estimation is developed. The 230Th/U dating method has evolved along broadly similar lines, but with a discontinuity arising from the revolutionary application by Chen et al. (1986) and Edwards et al. (1987) of TIMS (thermal ionization mass spectrometry), which not only improved the precision of the analyses by an order of magnitude, but also changed the “culture” and mind-set of the practitioners from a small community trained largely in AS (alpha spectrometry) to a larger community that included the TIMS and ICP-MS (inductively-coupled polarization mass-spectrometry) laboratories as well. At this writing, these two cultures have not completely integrated their approaches, so that there is little practical consensus on a “standard” way of evaluating common types of 230Th/U data-sets for geochronology, in contrast to geochronology by the U-Pb, Rb-Sr, or Ar-Ar methods. The viewpoint taken in this chapter is to outline the basic tools of data handling and evaluation for 230Th/U geochronology, while at the same time pointing out the limitations of these tools and possible directions of improvement.
Though this chapter is focused on the 230Th/U method, most of the concepts are directly applicable to other uranium-series chronometers, such as 231Pa/235U, 231Pa/230Th or 226Ra/230Th. However, because the details of individual applications of these methods are more varied than for the 230Th/U method, and in …