Radiogenic isotopes

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Radiogenic isotopes
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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)

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

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