U_Pb_Geochronology

Example zircon just as important however is nding u

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Unformatted text preview: b Dating • • Key with U-Pb dating is finding U-rich minerals. • Example: Zircon Just as important, however, is finding U-rich minerals with very low common Pb (common Pb increases errors and gives less precise ages). • • • • Takes U into its structure, but excludes Pb. By comparing the amount of Pb derived from radioactive decay, relative to the amount of U present we can get ages for the rocks. Hence, any Pb present in the zircon grain has come from radiogenic breakdown of U. More on this later...... Wednesday, 15 August, 12 Common Minerals Used for U-Pb Dating Uranium Common Pb Range (ppm) ( ppm) Mineral Formula Rock Type Zircon ZrSiO4 1-10000 <2 Most Baddeleyite ZrO2 58-3410 <2 K,C,UM,M,A Monazite CePO4 282-13730 <2 SG,GP,PS,HV Titanite CaTiSiO5 4-500 5-40 Most,SK Rutile TiO2 <1-390 <2-95 GP,GN,HV Perovskite CaTiO3 21-348 <2-90 K,C Apatite CaPO4 5-114 <5-30 Most Allanite CaFeAl2Si3O12 130-600 5-30 IG Xenotime YPO4 5000-29000 <5 SG Thorite Th(SiO4) >50000 <2 GP,SG K = kimberlite, C = carbonatite, UM = ultramafic, M = mafic, A = alkaline, SG = S-type granitoids, IG = I-type granitoids, GP = granitic pegmatite, HV = hydrothermal veins...
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This document was uploaded on 03/06/2014 for the course ES 4502 at Memorial University.

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