Table 3.
Laser argon isotopic results for MZ-7 plagioclase
| Step | 40Ar/39Ar | 37Ar/39Ar | 36Ar/39Ar (×10−3) | 39ArK (×10−15 mol) | K/Ca | 40Ar*, % | Age, Ma | ±1 σ, Ma |
|---|---|---|---|---|---|---|---|---|
| 06 | 41.84 | 15.86 | 63.42 | 0.341 | 0.032 | 58.1 | 35.26 | 0.51 |
| 05 | 41.95 | 14.01 | 63.00 | 0.349 | 0.036 | 58.2 | 35.34 | 0.46 |
| 04 | 56.79 | 13.20 | 111.1 | 0.385 | 0.039 | 44.0 | 36.15 | 0.52 |
| 07 | 39.31 | 14.00 | 51.69 | 0.272 | 0.036 | 63.9 | 36.34 | 0.53 |
| 09 | 36.43 | 15.80 | 42.08 | 0.289 | 0.032 | 69.2 | 36.54 | 0.46 |
| 08 | 79.53 | 6.180 | 180.0 | 0.034 | 0.083 | 33.7 | 38.6 | 6.7 |
| 03 | 49.56 | 16.21 | 81.49 | 0.162 | 0.03 | 53.9 | 38.7 | 1.2 |
| Weighted mean age | 0.041 ± 0.018 | 36.01 | 0.44** | |||||
MZ-7 plagioclase sample masses = 1–3 mg, J = 0.0008025, Laboratory sample 8955. Isotopic ratios are corrected for blank, radioactive decay, and mass discrimination, not corrected for interfering reactions. Individual analyses show analytical error only; plateau, preferred, and total gas age errors includes error in J and irradiation parameters. K/Ca = molar ratio calculated from reactor-produced 39ArK and 37ArCa. For calculation of the weighted mean age (n = 7), mean standard weighted deviation (MSWD) = 1.92. **, 2 σ error.