Table 2.

Furnace argon isotopic results for MZ-7 plagioclase

Step	Temp, °C	40Ar/39Ar	37Ar/39Ar	36Ar/39Ar (×10−3)	39ArK (×10−15 mol)	K/Ca	40Ar*, %	39Ar, %	Age, Ma	±1 σ, Ma
A	700	82.37	4.689	177.9	0.068	0.11	36.6	5.9	43.3	6.5
B	900	28.34	12.52	16.22	0.246	0.041	86.5	27.1	35.4	1.7
C	1100	32.52	19.87	19.68	0.241	0.026	86.8	47.9	41.0	1.8
D	1300	33.21	19.35	34.09	0.341	0.026	74.1	77.4	35.8	1.3
E	1650	45.16	24.43	63.22	0.262	0.021	62.8	100.0	41.3	1.9
Total gas age					1.16	0.033			38.5	1.9
Preferred age					1.16	0.033		100.0	37.9	2.7**

MZ-7 plagioclase, sample mass = 4.16 mg, J = 0.0008025, Laboratory sample 8955-02. For calculation of both ages, n = 5. For preferred age from steps A–E, mean standard weighted deviation (MSWD) = 2.87 (outside of 95% confidence interval). **, 2 σ error.