U_Pb_Geochronology

If the two ages and pb pb age are coincident they are

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Unformatted text preview: f not they are DISCORDANT. • We can view the behaviour of the UPb system using a CONCORDIA DIAGRAM. Wednesday, 15 August, 12 Concordia Diagrams From Richards and Noble (1998) Wednesday, 15 August, 12 CONVENTIONAL U-PB CONCORDIA PLOT concordant U-Pb analysis 206 Pb/238U age = 1500 ± 60 Ma 0.3 Pb/235U age = 1500 ± 40 Ma 207 Pb/206Pb age = 1500 ± 20 Ma 1600 206Pb/238U 207 1400 1200 0.2 1000 800 600 0.1 400 discordant analysis 206 Pb/238U age = 1150 ± 60 Ma Pb/235U age = 1300 ± 50 Ma 207 Pb/206Pb age = 1750 ± 50 Ma 207 0.0 0.0 2.0 4.0 207Pb/235U From Mortensen and Tosdal (1998) Wednesday, 15 August, 12 CONVENTIONAL U-PB CONCORDIA PLOT episodic Pb-loss model 0.3 1600 concordant U-Pb analysis + 206Pb/238U 1400 1200 0.2 1000 1 Ga Pb-loss 800 + + ++ + + crystallization age discordant U-Pb analyses + 600 0.1 400 inferred age of episodic Pb-loss event 0.0 0.0 0 Ma Pb-loss 4.0 2.0 207Pb/235U From Mortensen and Tosdal (1998) Wednesday, 15 August, 12 CONVENTIONAL U-PB CONCORDIA PLOT inheritence model minimum age range of inherited zircon components = 1 Ga - 1.8 Ga 0.3 1600 206Pb/238U 1400 1200 + 0.2 + 1000 crystallization age 800 600 0.1 400 + + + + inherited c...
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This document was uploaded on 03/06/2014 for the course ES 4502 at Memorial University.

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