Radiogenic isotopes

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)

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

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

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.

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.

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