U–Pb analyses of zircon in a metarhyolite (AF94-DD2) from the Delaney Dome Formation (modified from Friedrich 1998)

ConcentrationErrors 2-s (%)Age (Ma)d
FractionWeight (μg)U (ppm)Pb (ppm)206Pba/204Pb208Pb/206Pbb206Pb/238Uc% err207Pb/235Uc% err207Pb/206Pbc% err206Pb/238U207Pb/235U207Pb/206Pbcorr. coef.Pbe (pg)Pba/Pbe
Z4(1)2.9115.519.92263.60.1190.16785(.14)1.70760(.21)0.07378(.15)1000.31011.41035.50.6981.635.8
Z5(1)0.8436.833.9754.10.1540.07461(.30)0.58163(.60)0.05654(.49)463.9465.5473.60.5782.311.9
Z7(1)0.9679.980.13562.60.0730.11843(.16)1.35468(.17)0.08296(.07)721.5869.61268.30.9231.354.7
Z8(1)1.2354.248.42934.40.0320.14394(.10)1.43300(.14)0.07221(.08)866.9902.8991.80.7821.443.0
Z9(1)0.9627.136.12630.00.1130.05719(.22)0.44633(.30)0.05660(.19)358.5374.7476.10.7790.840.8
Z10(1)1.0499.423.52104.40.1990.04343(.26)0.33903(.32)0.05661(.18)274.1296.4476.60.8350.735.0
Z11(1)1.2468.129.22397.30.1590.05968(.15)0.46561(.30)0.05659(.25)373.7388.1475.40.5410.938.6
Z12(1)1.1284.016.1979.70.1560.05446(.32)0.42488(.43)0.05658(.28)341.9359.5475.20.7571.115.6

a Radiogenic Pb.

b Measured ratio corrected for spike and fractionation only. Mass fractionation correction of 0.15%/amu ± 0.04%/amu was applied to single collector Daly analyses and 0.12%/amu ± 0.04% for dynamic Faraday–Daly analyses.

c Corrected for fractionation, spike, blank, and initial common Pb.

d Age calculations are based on the decay constants of Steiger & Jäger (1977).

e Total common Pb in analysis. Total procedural blank for Pb ranged from 0.65–3.7 pg and < 1.0 pg for U. Blank isotopic composition: 206Pb/204Pb = 19.10 ± 0.1, 207Pb/204Pb =15.71 ± 0.1,208Pb/204Pb = 38.65 ± 0.1.

All errors are reported as 2σ. Number of zircons in each fraction shown in parentheses after fraction name. Sample weights are estimated using a video monitor with gridded screen and are known to within 40%. Common Pb corrections were calculated using the model of Stacy & Kramers (1975) and the interpreted age of the sample.