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U-Pb Concordia/Discordia Dating Techniques

U-Pb Concordia/Discordia Dating Techniques. Decay of 238 U to 206 Pb and 235 U to 207 Pb System behavior = exponential decay If/then/else logical statements introduced to remove Pb or U at specified time Start with simple 2 and 3 isotope decay series to learn about secular equilibrium.

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U-Pb Concordia/Discordia Dating Techniques

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  1. U-Pb Concordia/Discordia Dating Techniques • Decay of 238U to 206Pb and 235U to 207Pb • System behavior = exponential decay • If/then/else logical statements introduced to remove Pb or U at specified time • Start with simple 2 and 3 isotope decay series to learn about secular equilibrium

  2. 238U decay to 206Pb 234U 238U 234Pa 230Th 234Th 226Ra 218Rn 222Rn 218At 210Po 214Po 218Po 210Bi 214Bi 206Pb 210Pb 214Pb 206Tl 210Tl 206Hg

  3. Basic model of U decay Lead_206(t) = Lead_206(t - dt) + (Decay) * dt INIT Lead_206 = 0 INFLOWS: Decay = Uranium_238__Decay_Constant*Uranium_238 Uranium_238(t) = Uranium_238(t - dt) + (- Decay) * dt INIT Uranium_238 = 1*10^9 OUTFLOWS: Decay = Uranium_238__Decay_Constant*Uranium_238 Uranium_238__Decay_Constant = LOGN(2)/Uranium_238_Half_Life Uranium_238_Half_Life = 4468

  4. Model incorporating both decay systems and Metamorphic loss or gain of isotopes (e.g. Lead_206_Outflow = IF(TIME=1500)THEN(0.1*Lead_206/DT)ELSE(0)

  5. Age of rock = 3.5 billion years 20% 30% Time of lead loss = 1.5 billion years, ratios give time = 2 billion years, which reflects the time elapsed since lead loss 235U half life shorter than 238U so 207Pb/235U ratio larger than 206Pb/238U

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