1. Radiogenic isotopes

2. Isotopes Same number of protons, different number of neutrons (same atomic number, different atomic masses) Same chemical properties… … but different masses Chemical etc. processes fraction only slightly isotopes (mostly the lights)

3. Stable isotopes –See GEOL214 –Used largely for surface processes, some use as magmatic tracers Unstable isotopes –Parent -> daughter –Used for dating –Tracers of sources

4. Isotopic systems Used for dating –K-Ar –Rb-Sr –Sm-Nd –U-Pb (and Pb-Pb, and more) Used as tracers –Sm-Nd –Rb-Sr –Pb-Pb –Lu-Hf –Re-Os See G.214

7. The U-Pb-Th System Concordia = Simultaneous co-evolution of 206 Pb and 207 Pb via: 238 U  234 U  206 Pb 235 U  207 Pb Figure 9-16a. After Faure (1986). Principles of Isotope Geology. 2nd, ed. John Wiley & Sons. New York.

8. The U-Pb-Th System Discordia = loss of both 206 Pb and 207 Pb Figure 9-16a. After Faure (1986). Principles of Isotope Geology. 2nd, ed. John Wiley & Sons. New York.

9. The U-Pb-Th System Concordia diagram after 3.5 Ga total evolution Figure 9-16b. After Faure (1986). Principles of Isotope Geology. 2nd, ed. John Wiley & Sons. NY Figure 9-16b. After Faure (1986). Principles of Isotope Geology. 2nd, ed. John Wiley & Sons. NY