Table 1. 40Ar-39Ar incremental heating ages for basalt and plagioclase.
| Plateau | Isochron | ||||||
|---|---|---|---|---|---|---|---|
| Sample Number | 39Ar (%) |
Age ± 1 (Ma) |
Age ± 1 (Ma) |
Intercept ±
1 |
Sum/ (N-2) |
N | |
163-988A- |
|||||||
3R-2, 70-76 PL |
80 |
49.4 ± 0.3 |
47.5 ± 1.8 |
349.7 ± 18.5 |
1.25 |
6 |
|
3R-3, 17-22 WR |
100 |
49.4 ± 0.5 |
49.8 ± 1.2 |
295.4 ± 3.6 |
1.76 |
6 |
|
3R-3, 17-22 WR |
74 |
51.1 ± 1.0 |
50.0 ± 2.2 |
302.7 ± 9.5 |
0.51 |
4 |
|
3R-3, 17-22 WR |
96 |
49.7 ± 0.3 |
47.3 ± 1.6 |
325.5 ± 11.3 |
1.56 |
5 |
|
163-989B- |
|||||||
4R-2, 102-10 WR |
100 |
57.1 ± 1.4 |
54.1 ± 1.2 |
297.4 ± 1.2 |
0.96 |
6 |
|
5R-2, 28-33 WR |
89 |
57.1 ± 3.8 |
57.9 ± 3.8 |
296.9 ± 2.6 |
1.17 |
5 |
|
11R-1, 138-143 WR |
No plateau developed (recoil release pattern) | ||||||
163-990A- |
|||||||
3R-1, 56-60 WR |
100 |
56.2 ± 1.3 |
54.8 ± 2.2 |
297.4 ± 2.6 |
1.00 |
6 |
|
7R-2, 50-56 WR |
90 |
55.4 ± 0.7 |
55.1 ± 0.7 |
283.4 ± 6.9 |
0.68 |
5 |
|
16R-3, 88-91 WR |
No plateau developed (recoil release pattern) | ||||||
16R-4, 7-11 WR |
82 |
56.0 ± 0.9 |
55.0 ± 1.0 |
296.6 ± 1.6 |
0.29 |
5 |
|
17R-3, 104-109 WR |
79 |
55.5 ± 2.2 |
54.8 ± 2.3 |
296.0 ± 1.8 |
0.48 |
4 |
|
17R-4, 24-28 PL |
No plateau developed | 56.1 ± 2.9 |
362.0 ± 27.0 |
1.85 |
6 |
||
19R-5, 21-26 WR |
65 |
55.2 ± 1.4 |
57.1 ± 1.7 |
293.6 ± 3.0 |
1.70 |
4 |
|
Notes: Ages
are reported relative to biotite monitor FCT-3 (27.84 ± 0.12
Ma), which is calibrated against hornblende Mmhb-1 (520.4 Ma;
Samson and Alexander, 1987). Plateau ages are the mean of
concordant step ages (N = number of steps), weighted by
the inverse of their variances. Calculations use the following
decay and reactor interference constants: 
= 0.581
× 10-10 yr-1, ß =
4.963 × 10-10 yr-1; (36Ar/37Ar)Ca
= 0.000264, (39Ar/37Ar)Ca =
0.000673, (40Ar/39Ar)Ca = 0.01.
PL = plagioclase separate, WR = whole rock.