U_Pb_Geochronology

Common pb all 204pb and 206207pb204pbo wednesday 15

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Unformatted text preview: tope ratios o λ1, λ2 = decay constants. COMMON Pb = all 204Pb and 206,207Pb/204Pbo Wednesday, 15 August, 12 U-Pb Isotope System • In most minerals we aim to have no common Pb as it increases error. With this we can rewrite the above to have equations with no common Pb (i.e., we can remove 204Pb and 206,207Pb/204Pb): 206,207Pb* = Pb derived from radiogenic breakdown of U. 238,235U = U present in the minerals. λ1, λ2 = decay constants • Since we have two decay schemes we get two independent ages for a mineral/rock. • • If the ages are the same they are CONCORDANT. If the ages are different they are DISCONCORDANT. Wednesday, 15 August, 12 U-Pb Isotope System • By dividing the above equations we also get what is called the 207Pb/206Pb age (Pb-Pb age). 206,207Pb* = Pb derived from radiogenic breakdown of U. 238,235U = U present in the minerals. λ1, λ2 = decay constants • This is solved iteratively and these ages are often used for discordant data arrays (we’ll see significance of this in future slides). Wednesday, 15 August, 12 Minerals for U-P...
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This document was uploaded on 03/06/2014 for the course ES 4502 at Memorial University.

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