Pb isotope

For example, after successively emitting eight helium nuclei and six beta particles from the end result is the non-radioactive Pb isotope. 

For example, the presence of Sr in the absence of the more abundant Sr (82.7%) would clearly indicate that its origin is from the decay of Rb. For the Pb isotopes, a more detailed set of measurements might be needed. In this case the normal Pb abundances can be altered by the presence of any or all of the indicated Th and U isotopes, so not only the abundances of the Pb isotopes, but also those of the potential parent isotopes must be determined. 

A sample of lead atoms is analyzed by mass spectrometry. The bar graph in the margin shows the results. Use information from the graph to write the elemental symbol that represents each Pb isotope and estimate the natural abundance of each. List the number of protons and neutrons for each isotope. 

The four peaks in the mass spectrum represent four Pb isotopes. Their A values are 204, 206, 207, and 208. Consulting the periodic table, we find that Z of lead is 82. Thus, the elemental symbols are as 204 206. 207 208... 

Fig. 2.57. Pb isotopic compositions in volcanogenic Cu sulfide deposits in Japan. Diamond shape K], K2 and K3 indicate average values of Kuroko-type deposits Ki Taro (Cretaceous) K2 Northeast Japan (Miocene) K3 southwest Japan (Miocene). Note that the Shimokawa ores (solid square, Besshi subtype) and Yanahara ores (open square, Hitachi subtype), closely associated with sediments, tend to have slightly more radiogenic values than the others (solid circles) (Sato and Kase, 1996).

LeHuray, A.P., Church, S.E., Koski, R.A. and Bouse, R.M. (1988) Pb isotopes in sulfides from midocean ridge hydrothermal sites. Geology, 16, 362-365. 

Belshaw NS, Freedman PA, O Nions RK, Frank M, Guo Y (1998) A new variable dispersion double focusing plasma mass spectrometer with performance illustrated for Pb isotopes. Inti J Mass Spectrom 181 51-58... 

Because the ( °Th)/( Th) of any material after 350,000 years will depend on the material s Th/U, the behavior of Th isotopes in the mantle is intrinsically different from that of Sr, Nd and Pb isotopes. In principle, Th isotopes could provide information about discrete recent depletion and enrichment events. Unfortunately, this interpretation is not straightforward if Th isotopes are significantly modified from the original mantle source value by ingrowth during the melting process. 

O Hara MJ (1968) The bearing of phase equilibria studies in synthetic and natural systems on the origin and evolution of basic and ultrabasic rocks. Earth Sci Rev 4 69-133 O Nions RK, McKenzie D (1993) Estimates of mantle thorium/uranium ratios from Th, U and Pb isotope abundances in basaltic melts. Phil Trans Royal Soc 342 65-77 Oversby V, Gast PW (1968) Lead isotope compositions and uranium decay series disequilibrium in reeent volcanic rocks. Earth Planet Sci Lett 5 199-206... 

The presence of °Be or negative Ce anomalies, or both, in some arc lavas provide unambiguous evidence for a contribution from subducted sediments to the source of arc lavas (Morris et al. 1990 Hole et al. 1984). In addition, Pb isotopes commonly are... 

Hoogewerff JA, van Bergen MJ, Vroon PZ, Hertogen J, Wordel R, Sneyers A, Nasution A, Varekamp JC, Moens HLE, Mouchel D (1997) U-series, Sr-Nd-Pb isotope and trace-element systematics across an active island arc-continent collision zone impUcations for element transfer at the slab-wedge interface. Geochim Cosmochim Acta 61 1057-1072... 

Reagan MK, Sims KW, Erich J, Thomas RB, Cheng H, Edwards RL, Layne G, Ball L (2003) Timescales of differentiation from mafic parents to rhyolite in North American continental arcs. J Petrol (in press) Regelous M, Collerson KD, Ewart A, Wendt JI (1997) Trace element transport rates in subduction zones evidence from Th, Sr and Pb isotope data for Tonga-Kermadec arc lavas. Earth Planet Sci Lett 150 291-302... 

Tinner S, Foden J (2001) U, Th and Ra disequilibria, Sr, Nd and Pb isotope and trace element variations in Sunda arc lavas predominance of a subducted sediment component. Contrib Mineral Petrol 142 43-57 Turner S, Evans P, Hawkesworth C, (2001) Ultra-fast source-to-surface movement of melt at island arcs from Ra- °Th systematics. Science 292 1363-1366... 

Since the subsequent B-decays of Pb-212 and Pb-214 4- Bi-214 do not result in significant recoil (Mercer, 1976), the alpha measurement of Po-214 and the Pb-212 daughters is in reality tracing the aerosol distribution of a Rn-220 daughter atom (Pb-212) which has condensed only once and a Rn-222 daughter atom (Pb-214) that has probably condensed more than once. This stability of the Pb isotopes is the basis for our generic reference to Pb-212 and Pb-214 distributions. 

Table 4.4. Contours of the 95 percent confidence ellipse of the mean for the Pb isotope composition...

The loading matrix FA1/2 given by equation (4.4.26) can be found in Table 4.14. Lead isotopes have strong correlation coefficients on the first component. They are decoupled from Sr and Nd isotopes which strongly correlate and anticorrelate, respectively, with the second component. On a global scale, Pb isotopic variations in oceanic islands seem to be decoupled from Sr and Nd isotopic variations. 

Table 5.23. Pb isotope composition of Archean granites from Zimbabwe (courtesy...

Ludwig, K. R. (1980). Calculation of uncertainties of U-Pb isotope data. Earth Planet. Sci. Letters, 46, 212-20. 

Corrections for instrumentally-produced mass fractionation that preserve natural mass dependent fractionation can be approached in one of two ways a double-spike method, which allows for rigorous calculation of instrumental mass fractionation (e.g., Dodson 1963 Compston and Oversby 1969 Eugster et al. 1969 Gale 1970 Hamelin et al. 1985 Galer 1999 see section Double-spike analysis ), or an empirical adjustment, based on comparison with isotopic analysis of standards (Dixon et al. 1993 Taylor et al. 1992 1993). The empirical approach assumes that standards and samples fractionate to the same degree during isotopic analysis, requiring carefully controlled analysis conditions. Such approaches are commonly used for Pb isotope work. However, it is important to stress that the precision and accuracy of isotope ratios determined on unknown samples may be very difficult to evaluate because each filament load in a TIMS analysis is different. 

---