Table 1. 40Ar/39Ar results.
%39Arfeld is the cumulative percentage of 39Ar released from the feldspathic portion of the age spectrum that is included in the age calculation. The preferred age for each sample is the plateau age, shown in bold. Data were corrected for cosmogenic Ar using an apparent 38Ar exposure age of 4.77 ± 0.54 Ma (see Table 3). Age spectra were corrected for trapped 40Ar using a 40Ar/36Ar ratio of 576 ± 208, based on the weighted average y intercept of seven isochrons. See the Supplementary Materials for a list of extractions included in isochron regressions and plateau age calculations and for a description of the statistical approach used to interpret age spectra and isochrons and to calculate weighted averages.
| Aliquot | Phase | Isochron analysis | Age spectrum analysis | ||||||
| Age ± 2σ (Ma) | (40Ar/36Ar)trap ± 2σ | MSWD | Prob. | %39Arfeld | Age ± 2σ (Ma) | MSWD | %39Arfeld | ||
| SUERC-1 | WR frag | Does not meet isochron criteria | <1300 Ma—did not yield concordant ages | ||||||
| SUERC-2 | WR frag | 1224 ± 52 | 542 ± 150 | 0.3 | 0.57 | 52 | 1191 ± 32 | 0.6 | 92 |
| SUERC-3 | WR frag | 1347 ± 24 | 869 ± 118 | 0.9 | 0.42 | 52 | 1391 ± 16 | 0.8 | 52 |
| SUERC-4 | WR frag | No spread on isochron | 1365 ± 16 | 0.7 | 64 | ||||
| SUERC-5 | WR frag | 1350 ± 38 | 267 ± 140 | 0.9 | 0.46 | 61 | 1266 ± 14 | 1.0 | 76 |
| SUERC-6 | WR frag | 1334 ± 70 | 310 ± 280 | 1.8 | 0.13 | 59 | 1288 ± 32 | 1.2 | 59 |
| SUERC-7 | WR frag | Does not meet isochron criteria | 1346 ± 15 | 0.9 | 89 | ||||
| SUERC-8 | WR frag | 1330 ± 37 | 808 ± 230 | 1.9 | 0.13 | 76 | 1371 ± 16 | 0.7 | 76 |
| SUERC-9 | WR frag | Does not meet isochron criteria | 1345 ± 17 | 1.3 | 69 | ||||
| SUERC-10 | WR frag | No spread on isochron | 1383 ± 16 | 1.8 | 56 | ||||
| SUERC-11 | WR frag | 1367 ± 44 | 534 ± 390 | 1.0 | 0.42 | 100 | 1367 ± 11 | 0.6 | 100 |
| LLNL-1 | WR frag | 1337 ± 23 | 530 ± 100 | 1.3 | 0.22 | 86 | 1327 ± 12 | 0.3 | 95 |
| LLNL-2 | WR frag | Does not meet isochron criteria | <1300 Ma—did not yield concordant ages | ||||||
| Weighted average: | 576 ± 208 | 8.8 | |||||||
| SUERC-12 | Feldspar | Does not meet isochron criteria | >2000 Ma—did not yield concordant ages | ||||||
| SUERC-13 | Feldspar | Does not meet isochron criteria | 1374 ± 7* | 7.2 | 100 | ||||
| SUERC-14 | Feldspar | Does not meet isochron criteria | >1400 Ma—did not yield concordant ages | ||||||
| LLNL-3 | Feldspar | Does not meet isochron criteria | >2000 Ma—did not yield concordant ages | ||||||
*The SUERC-13 feldspar age represents the weighted average of all extraction steps and does not satisfy plateau age criteria.