Tera–Wasserburg diagram

English

Alternative forms

Etymology

Named after geologists Fouad Tera and G. J. Wasserburg. From circa 1972.

Noun

Tera–Wasserburg diagram (plural Tera–Wasserburg diagrams)

(geology, geochronology) A type of concordia diagram, used in the context of uranium–lead dating, whose axes are the ratios ²⁰⁷Pb/²⁰⁶Pb and ²³⁸U/²⁰⁶Pb.
The axes of the Tera–Wasserburg diagram are the amounts of ${\ce {^{207}Pb}}$ (a stable, radiogenic isotope unconnected with uranium series decay) and ${\ce {^{238}U}}$ (the start of the uranium series decay chain), each adjusted and expressed as ratio to the amount of ${\ce {^{206}Pb}}$ (the stable end product of the uranium series).

One feature of the Tera–Wasserburg diagram is that for samples whose original lead content was both high and of unknown isotopic composition, the plotted points may lie on an isochron whose intersection with the ${\ce {^{207}Pb/^{206}Pb}}$ axis gives the original lead composition and whose intersection with the concordia curve yields the age.
- 2012, Frank Vanhaecke, Patrick Degryse, Isotopic Analysis, Wiley-VCH, page 252:
  Unfortunately, zircons that have high common Pb contents often also display Pb loss. This can be checked in a Tera–Wasserburg diagram, provided that the zircons belong to a single population, since common-Pb correction should reduce the data to a single point on the concordia.
- 2016, Bruce F. Schaefer, Radiogenic Isotope Geochemistry, Cambridge University Press, page 103:
  For all practical purposes, such distinctions are generally significant more for the specialist geochronologists rather than the geologists who are interested in using the geochronological data; however, it is important to be aware that there are subtle differences between the types of Tera–Wasserburg diagrams that can be plotted and hence how the ages can be interpreted.
- 2018, Alan P. Dickin, Radiogenic Isotope Geology, 3rd edition, Cambridge University Press, page 116:
  Fig. 5.32 Meteorite mineral data on (a) Pb–Pb isotope and (b) Tera–Wasserburg diagrams, representing the back and front faces of the total-Pb/U isochron diagram.