Concordia

G. Zambon" Chemistry Research Institute, Italy Dead Sea Bromine Group, Israel Ben-Gurion University of the Negev, Israel The Hebrew University of Jerusalem, Israel University de Paris VII - C.N.R.S., France Tel Aviv University, Israel University College of Swansea, UK Concordia University, Canada University de Louvain, Belgium The Weizmann Institute of Science, Israel... 

Figure 4. vs. concordia diagram (after Cheng et al. 1998). Concordia represent the... 

Figure 5. Concordia diagram similar to Figure 4 illustrating the concordia curve for initial = 150 (appropriate for marine samples), with age in ka depicted parametrically along concordia. Also illustrated are continuous uranium gain/loss model curves for samples with primary ages of 80 ka (dashed) and 150 ka (thin solid curve). See text for discussion of this model and related models (after Cheng etal. 1998).

Concordia represents the isotopic composition of material that has lost uranium at a low rate. Points progressively higher on the curve represent progressively higher rates of uranium loss. The thin solid curve is analogous to the dashed curve, but pertains instead to a set of materials with a primary age of 150 ky. 

Figure 6. A portion of the concordia curve for initial =150 and four data points (Edwards et al. 1997) for coral samples from the last interglacial terrace in Barbados. The points lie along a hne, and illustrate the possibility of using best-fit lines through discordant points to extrapolate to concordia and possibly the tme age of a set of samples (after Cheng et al. 1998).

Edwards et al. (1997) demonstrate that for samples with similar " U(O), such as corals that grew in open marine water, and remained closed system since time of formation, isotopic data plot on or close to an ideal concordia in vs. °Th/ U... 

Figure 9. U, Th and Pa isotopic data and ages for speleothems (Beck et al. 2001 Mnsgrove et al. 2001, Dorale et al. 2003). A.) vs. concordia plot. Evolntion cnrves for different 5 " U(0)...

A unique strength of concordia diagrams is their ability to reveal modes of diagenetic disturbance. If U-Th-Pa isotopic data for numerous co-eval sub-samples that have experienced different degrees of the same diagenetic process are plotted in or vs. space, they should fall on a curve or straight line... 

Figure 10. Modified Tera-Wasseibuig f° Pb/ ° Pb-2 U/2 Pb) plot with disequilibrium concordia (after Wendt and Carl 1985). The curvilinear trajectories (dotted lines), or concordia, show the change in 23 U/ 06p ) 207p y206p ggg incrcascs for different values of 8234u(0) and Pao = orh = 226Ra = q.

Figure 13. Tera-Wasserbnrg style three-dimensional concoidia plot for the WHCl stalactite (Richards et al. 1988). Shown is the projection onto the U/ ° Pb- ° Pb/ ° Pb plane (see Fig. 10 caption). The intercept of the three-dimensional fit with this plane is shown by the shaded error ellipse. A) Three-dimensional regression, disequilibrium concordia (5 " U(0) = 320 dashed line], and plane intercept. B) Detail of intercept with 2 U/ ° Pb- ° Pb/ Pb plane, disequilibrium concordia (2o error), regression line, and the secular equilibrium concordia.

Allegre CJ (1964) De I extension de la methode de calcul graphique Concordia aux measures d ages absolus effctues a I aide du desequilibre radioactif. Cas ds mineralisations secondaires d uanium. C R Acad Sci Paris 259 4086-4089... 

W. J. Chazin, Ph.D. Thesis, Concordia University, Montreal, Quebec, Canada, 1983. 

Associate Professor, Department of Electrical and Computer Engineering, Concordia University, Montreal, Canada... 

In order to complete this chapter, I had to call on the help of three friends, who I would like to acknowledge. First, I thank Dr. Luc Varin for providing me with unfettered access to his office at the Loyola campus of Concordia, away from the distractions of Montreal s downtown. I also am thankful to Imad Hoteit for reading and providing detailed feedback on the first draft of the chapter. Last, but not least, I would like to thank Mohammad Ebne-Alian for the excellent technical drawings and recreations used to illustrate parts of this chapter. 

C.H. Langford, Concordia University Dr. Wrighton s paper maintains appropriate discretion with respect to the twenty-first century. As Neils Bohr said, "Prediction is difficult, especially about the future". However, he does call attention to a number of problems in solid state and interfacial chemistry which are certainly important now and would not have been likely to be picked out for emphasis in a meeting of inorganic chemists held ten years ago and oriented to the theme of... 

Using two different initial guesses (5 and OGa) in order to approach the two intersections from different directions, Table 3.4 gives the results of the first iterations towards each intersection. The zircon alignment intersects the Concordia at 1.00 and 2.00 Ga. o... 

Table 3.4. Iterative calculation of the two age intercepts with the Concordia curve for a zircon linear array having a slope a = 0.256 and an intercept =0.094613.

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