Campaign-style titanite U-Pb dating by ICP - Earth Science ...

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626627628629630631632633634635636637638639640641642643644645646647648649A5. LA-ICP-MS Analytical TechniqueSamples were ablated either in thin section or in grain mount (Table 1) using a PhotonMachines 193 nm ArF excimer ultraviolet laser with a HelEx ablation cell coupled to aNu Instruments Plasma high-resolution multi-collector inductively coupled plasmamass spectrometer (MC-ICPMS) (Table A5). The laser spot diameter was 30 or 40 µmand the laser fluence was ~1 J/cm 2 . The laser was fired twice to remove common Pbfrom the sample surface and this material was allowed to wash out for 10 seconds.Material was then ablated at 4 Hz for 20 seconds, resulting in a pit depth of ~8 µm.Masses 204 Pb+Hg, 206 Pb, 207 Pb, and 208 Pb were measured on ion counters, and masses232 Th and 238 U were measured on Faraday detectors. Analyses of unknowns werebracketed by analyses of titanite primary reference materials (RM) BLR or Ontario-2(Table A6). At least one secondary titanite reference material (Table A6) was alsoincluded in each run as a monitor of accuracy: BLR, Ontario-2, the in-house titanitestandard Y1710C5 (Table 2), or the McClure Mtn (MM) titanite (Table A5).The Iolite plug-in [Paton et al., 2011] for the Wavemetrics Igor Pro software was usedto correct measured isotopic ratios for baselines, time-dependent laser-induced interelementfractionation, plasma-induced fractionation, and instrument drift. Baselineintensities were determined prior to each analysis. The mean and standard error of themeasured ratios of the backgrounds and peaks were calculated after rejection of outliersmore than 2 standard errors beyond the mean. Long-term analysis shows that thisequipment and method are capable of measuring the baseline- and fractionationcorrected206 Pb/ 238 U of a primary reference material (e.g., Ontario-2) with a long-termprecision of ± 0.7% (Figure A1); the baseline- and fractionation-corrected 207 Pb/ 206 Pbcan be measured with a long-term precision of ± 0.4%.36
650651652653654655656657658659660661662663664665666667668669670671672The in-run uncertainty of isotopic ratios measured in secondary RMs and unknownsis, naturally, greater. Analysis of secondary RMs with homogeneous isotopic ratios (e.g.,zircon) demonstrates that the uncertainty of individual 206 Pb/ 238 U measurements isdominated by counting statistics and signal stability; a typical uncertainty can berepresented by the Tukey’s biweight mean of ~1.9% calculated for the >3400 unknownsreported here. In contrast, individual 207 Pb/ 206 Pb measurements are much moreprecise—Tukey’s biweight mean is 0.2%—and require an additional 2% external errorattributable either to variation in ablation or transport characteristics; this was added inquadrature.The 238 U/ 206 Pb and 207 Pb/ 206 Pb isotopic ratios for each analysis were plotted on Tera–Wasserburg (1972) diagrams using Isoplot [Ludwig, 2003]. Because LA-ICP-MS allowsone to collect many analyses from the same titanite or the same sample, the analysesoften have sufficient spread in U/Pb ratios to define a 238 U/ 206 Pb– 207 Pb/ 206 Pb isochronwithout the need to assume a common 207 Pb/ 206 Pb ratio from a model [e.g., Stacey andKramers, 1975] model or from a low-U mineral presumed to be in equilibrium. All of theICP dates reported here are thus 238 U/ 206 Pb– 207 Pb/ 206 Pb isochrons. All dateuncertainties are reported at the 95% confidence interval, assuming a Gaussiandistribution of measurement errors.For samples with a broad spread of U-Pb ratios—and thus, a well-constrained common 207 Pb/ 206 Pb ratio—we report the 238 U/ 206 Pb–207 Pb/ 206 Pb isochron date. For samples with a small spread of U-Pb ratios—and thus, apoorly constrained common 207 Pb/ 206 Pb ratio—we anchor the ratio to the Stacey–Kramers [1975] value of 0.912 ± 0.05, appropriate for differentiation ages of 1660–400Ma.37
Page 1 and 2: Chemical Geology 341 (2013) 84-101C
Page 4 and 5: K.J. Spencer et al. / Chemical Geol
Page 8 and 9: Table 1 (continued)K.J. Spencer et
Page 20 and 21: 57657757857958058158258358458558658
Page 24 and 25: 67367467567667767867968068168268368
Page 26 and 27: Table 3a. Zr in titanite measuremen
Page 28 and 29: 173 374 2 818 15A0716A1_gr. 1 0 16
Page 30 and 31: 263 85 8 736 15A0718D_gr3 0 80 9 73
Page 32 and 33: 320 340 2 812 15360 332 2 811 15A07
Page 34 and 35: 23 98 7 743 1546 109 7 749 1569 105
Page 36 and 37: A0722G5_gr1 0 254 3 795 15163 266 3
Page 38 and 39: 61 197 4 781 15122 164 5 771 15183
Page 40 and 41: 198 342 2 812 15232 369 2 817 15264
Page 42 and 43: 26 350 2 814 1539 356 2 815 1552 33
Page 44 and 45: 272 391 2 820 15311 391 2 820 15350
Page 46 and 47: 227 168 4 772 15340 164 5 771 15453
Page 48 and 49: 598 60 12 719 15G9708Q4_gr. 3 0 75
Page 50 and 51: 482 80 9 733 15563 84 8 736 15643 5
Page 52 and 53: 642 12 59 645 201155 26 27 679 15P5
Page 54 and 55: 62 126 6 756 1582 142 5 763 15P5710
Page 56 and 57: 288 132 6 759 15360 172 4 773 15432
Page 58 and 59: 422 213 4 785 15475 129 6 758 15R98
Page 60 and 61: Table 4 appendix. Ontario-2 titanit
Page 62 and 63: 701702703704Appendix Table A5: Sett
Page 64 and 65: 8829A28830A1115 2.2 82 34 11.82 0.5
Page 66 and 67: 8912C3A0714L115 0.9 5 42 4.32 0.18
Page 68 and 69: A0715M2A0715R114 36.5 310 277 7.18
Page 70 and 71: A0717M34 5.9 201 68 14.39 0.16 0.13
Page 72 and 73:
A0718D5 4.7 771 115 15.01 0.34 0.08
Page 74 and 75:
A0720B1A0720J27 10.0 108 88 13.90 0
Page 76 and 77:
A0721E2A0721E47 7.9 1223 79 15.55 0
Page 78 and 79:
A0722B1A0722D110 7.5 791 28 15.20 0
Page 80 and 81:
A0722G5A0722H12 1.6 272 88 14.78 0.
Page 82 and 83:
A0724H4 6.0 317 222 14.01 0.17 0.10
Page 84 and 85:
A0726D1A0727C119 18.9 301 639 10.18
Page 86 and 87:
A0727N1A0801M23 2.6 1233 70 15.24 0
Page 88 and 89:
E9805KE9806B22 22.4 9 463 10.92 0.1
Page 90 and 91:
E9810C1E9814B222 3.8 25 45 5.16 0.1
Page 92 and 93:
G9702E1G9702FG9704G17 4.3 9 41 4.86
Page 94 and 95:
G9705YG9706N127 1.6 204 47 14.27 0.
Page 96 and 97:
G9707N1G9707R25 2.2 41 40 12.78 0.2
Page 98 and 99:
20 5.0 82 44 8.53 0.14 0.4336 0.009
Page 100 and 101:
K1725CK1727C125 2.1 7 50 2.75 0.17
Page 102 and 103:
K1729A1K1729F527 5.2 397 51 14.97 0
Page 104 and 105:
K1730G1K1730H120 1.3 278 21 15.01 0
Page 106 and 107:
K1802HK1802J129 7.8 110 54 11.39 0.
Page 108 and 109:
K7717KK7718I18 4.0 707 84 15.68 0.3
Page 110 and 111:
M8714G4 2.0 511 65 15.24 0.35 0.089
Page 112 and 113:
P5626H2P5626N16 6.8 523 42 13.65 0.
Page 114 and 115:
P5628E5P5628U4 4.3 83 76 13.89 0.23
Page 116 and 117:
P5630G2P5710A514 3.3 13 54 3.15 0.1
Page 118 and 119:
P6806B1P6806F1P6806G26 36.0 1662 68
Page 120 and 121:
P6807DP6809B18 2.4 3 42 1.08 0.07 0
Page 122 and 123:
P6815F2P6815G122 3.3 15 49 3.73 0.0
Page 124 and 125:
P6821A1P6824F1P6826I135 7.3 311 127
Page 126 and 127:
R9825E1R9828B211 11.2 216 48 9.43 0
Page 128 and 129:
R1617B19 1.8 61 49 11.07 0.21 0.312
Page 130 and 131:
Y0820C2Y0829J2Y1525A51 8.8 12 45 3.
Page 132 and 133:
25 17.8 24 50 1.25 0.02 0.8159 0.01
Page 134 and 135:
Paton, C., Hellstrom, J.C., Paul, B
Page 136 and 137:
0.170.15207 Pb206 Pbellipses are 2s
Page 138:
Figure 4a. Tera-Wasserburg diagrams
Page 141 and 142:
A0717J1A0718C10.200.18Intercept = 0
Page 143 and 144:
0.8A0721E40.28A0722B10.6Intercept =
Page 145 and 146:
0.5A0724HIntercept = 0.930 ± 0.013
Page 147 and 148:
1.0E9803K10.8E9806B20.80.6Intercept
Page 149 and 150:
1.1G9702E10.17G9705R10.9Intercept =
Page 151 and 152:
G9709K11.0J5810D0.24Intercept = 0.9
Page 153 and 154:
K1730A1K1730H11.00.80.60.5Intercept
Page 155 and 156:
M8710A1M8714G0.6Intercept = 0.912
Page 157 and 158:
1.0P5628E51.0P5630A30.8Intercept =
Page 159 and 160:
1.0P6814B1.10.9P6807C2Intercept = 0
Page 161 and 162:
R9828B20.80.6Intercept = 0.896 ± 0
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