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Table 2 Ar isotope data, cosmic ray exposure ages, 40Ar/39Ar ages for individual plagioclase-rich lithic fragments from Apollo 17, 78461 sample

From: 40Ar/39Ar and cosmic ray exposure ages of plagioclase-rich lithic fragments from Apollo 17 regolith, 78461

Sample 36Arm 37Arm 38Arm 39Arm 40Arm 38Arc
a
P38
sf
P38
avg
T38
sf
T38
avg
40Ar* 40Ar*/39ArK Age (Ga) 40Ar*/39ArK Age (Ga)
(10−6 cm3 STP/g) (Ma) (Ma) (%) (40Ar/36Ar)t = 0.146 (40Ar/36Ar)t = 0.0
Plag#1 0.8598 2.0115 0.2047 0.0252 8.8056 4.28 0.77 0.17 5.55 25.21 99 367.44 4.27 372.69 4.30
  ± 0.0015 ± 0.0072 ± 0.0004 ± 0.0005 ± 0.0044 ± 0.83 3.78 6.24 ± 0.05 6.25 ± 0.04
Plag#3 1.0202 2.1366 0.3207 0.0140 4.6721 12.9 0.75 0.16 17.27 78.16 97 364.99 4.26 376.87 4.32
0.0019 0.0095 0.0006 0.0003 0.0028 2.59 11.72 6.66 0.05 6.66 0.05
Plag#6 2.4610 1.5909 0.5121 0.0218 8.3324 4.92 0.73 0.16 6.75 30.69 96 388.51 4.37 405.82 4.44
0.0044 0.0090 0.0013 0.0008 0.0050 1.01 4.60 13.89 0.07 14.87 0.07
Plag#9 1.7646 1.9960 0.4568 0.0285 10.7986 12.5 0.76 0.17 16.33 74.24 98 391.73 4.38 401.19 4.42
0.0031 0.0072 0.0009 0.0004 0.0077 2.45 11.14 2.49 0.04 2.59 0.04
Plag#10 4.0690 1.9384 0.9513 0.0084 4.5744 18.6 0.77 0.17 24.20 109.47 87 578.00 5.03 663.19 5.26
0.0072 0.0068 0.0021 0.0002 0.0030 3.63 16.42 17.89 0.06 18.30 0.06
Plag#14 3.4637 2.0183 0.7720 0.0069 2.1377 12.1 0.76 0.17 15.82 71.55 76 303.48 3.96 396.18 4.40
0.0065 0.0074 0.0017 0.0001 0.0018 2.37 10.73   10.56 0.07 10.77 0.06
Plag#21 0.5082 1.2445 0.1361 0.0106 3.4686 4.04 0.76 0.17 5.34 24.18 98 353.29 4.21 360.92 4.25
0.0008 0.0041 0.0002 0.0001 0.0011 0.80 3.63 1.20 0.04 1.31 0.04
Plag#22 1.0221 1.8797 0.2122 0.0119 3.5167 2.00 0.78 0.17 2.57 11.77 96 323.01 4.06 337.15 4.13
0.0016 0.0063 0.0004 0.0001 0.0013 0.39 1.77 1.78 0.04 1.86 0.04
Plag#23 0.4147 1.6445 0.2482 0.0190 6.4346 17.0 0.79 0.17 21.53 97.48 99 359.57 4.24 362.95 4.25
0.0007 0.0055 0.0004 0.0002 0.0012 3.23 14.62 1.45 0.04 1.58 0.04
Plag#24 0.9031 1.3672 0.1915 0.0284 9.5823 2.14 0.76 0.17 2.81 12.79 99 346.31 4.18 351.08 4.20
0.0014 0.0048 0.0003 0.0003 0.0020 0.42 1.92 1.29 0.04 1.65 0.04
Plag#25 2.2802 1.6158 0.4375 0.0154 5.5328 0.87 0.78 0.17 1.11 5.05 94 369.07 4.28 392.43 4.38
0.0037 0.0056 0.0008 0.0002 0.0017 0.17 0.73 2.12 0.04 2.40 0.04
  1. The subscript m indicates that the measured abundance of Ar isotopes are corrected for blank contribution and mass discrimination. The subscript c indicates cosmogenic abundance determined by subtracting trapped component from the measured abundance of 38Ar. Please see the text for details. 40Ar*/39ArK and 40Ar/39Ar ages are given for two different methods (described in text) used for determining radiogenic 40Ar in the fragments. To determine the ratio 40Ar*/39ArK, measured 40Ar abundance is corrected for blank contribution, mass discrimination, and non-radiogenic trapped 40Ar (i.e., solar wind-implanted 40Ar) while measured 39Ar is corrected for blank contribution, mass discrimination, and corrected for reactor-produced 39Ar from 39K. 38Ar production rates are in units of 10−8 cm3 STP/g/Ma
  2. sf production rate calculated assuming lithic fragments were exposed to cosmic rays on lunar surface, avg production rate calculated based on average of production rates at the depth from 1 to 6 cm (corresponding shielding depth from 2 to 10 g/cm2)
  3. *Percentage of radiogenic component in measured 40Ar when corrected for trapped contribution (i.e., (40Ar/36Ar)t = 0.146)
  4. aUnits of (10−8 cm3 STP/g)
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