Concordia diagram

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).

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... 

Limiting ourselves to the observation of isotopic abundances determined by the 4n + 2 and 4n + 3 decay series, we can construct a concordia diagram (Wetherill, 1956) relating (206p /238 j 207pj /235 j ratios developing at... 

Figure 11,26 Concordia diagram. (A) Interpretation of straight discordia path as a result of a single episode of Pb loss. (B) Continuous diffusion model of Tilton (1960) applied to world minerals of a = 2800 Ma common age. Reproduced with modifications from G. Faure (1986), Principles of Isotope Geology, 2nd edition, copyright 1986 by John Wiley and Sons, by permission of John Wiley Sons and from Tilton (1960) by permission of the American Geophysical Union.

Why is the Tera-Wasserburg Concordia Diagram Concave Upward ... 

Wetherill s concordia diagram for interpreting discordant U-Pb dates caused by episodic loss of radiogenic lead. 

Figure 1 U-Pb Concordia diagram showing the results of an analysis of a detrital zircon crystal by ion microprobe (SHRIMP) followed by analysis of the same crystal using TIMS. Both error ellipses are plotted at 2a. The best estimate of the age of crystallization of the zircon is identical for both techniques however, the TIMS analysis is an order of magnitude more precise than that obtained using the ion microprobe (source Samson et aL, 2003).

BOX 1.1 FIGURE 3 U-Pb Concordia curve showing the compositions of individual analyses as error ellipses. The data, which are for a single grain, show that the grain has a core which is about 3,350 Ma old and a rim which is about 2,700 Ma old. The rim has experienced subsequent lead loss, giving rise to a series of discordant points on the Concordia diagram. This lead loss reflects a later thermal event at about 1,000 Ma. 

Figure 1. Concordia diagram illustrating misbehavior in the U-Th-Pb system that is relevant to U-Pb dating. Arrows show how concordant data can be affected by inheritance, Pb loss, disequilibrium, and common Pb (Pb°) corrections.

Figure 2. Concordia diagram of Himalayan monazite grains. References listed in the key. Note that a remarkable number these monazite grains show reverse discordance, consistent with incorporation of excess ° Pb.

AS data from Hodges et al. (1996), whereas MCT and DK data from Coleman (1998). See Figure 2 for a concordia diagram of this and other Himalayan monazite data. 

Pb isotopes with Because there are so many variables in lead isotopic systems (since we are dealing time with three different decay schemes) it is not convenient to display the data on the same type of rime vs isotope ratio diagram as is used for Sr and Nd isotopes, and the Concordia diagram is a better choice. On this diagram families of concordia (growth) curves can be drawn for different ratios ( i values) (Figure... 

Concordia diagram showing the effects of lead loss or uranium gain on U/Pb systems, fcryst is the time elapsed since original crystallization, fcios is the time elapsed since closure of the system after lead loss or uranium gain. A235 and A238 are the decay constants of the respective primary parents and... 

FIGURE 31.12 U-Pb age determination on zircon from Cinque Frati granite (Corsica, France). (A) Common-Pb uncorrected Tera and Wasserburg diagram for data obtained with LA-MC-ICP-MS (290.7 2.4 Ma [2o] MSWD = 2.7 [n = 20]). (B) Conventional Concordia diagram data corrected for common-Pb using Pb (ID-TIMS) (286.4 + 1.7 Ma [2oj MSWD = 1.2 [n = 7]). 

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