Table 1. Summary of 40Ar/39Ar results and analytical methods

ageSample Lab # Irradiation mineral analysis steps/analyses Age ±2σ MSWD commentsCAF-2-36362 63685 276 sanidine fusion 12 17.72 0.01 3.51 weighted mean

Sample preparation and irradiation: Minerals separated with standard heavy liquid, Franz Magnetic and hand-picking techniques.Samples in NM-276 irradiated in a machined Aluminum tray for 16 hours in C.T. position, USGS TRIGA, Denver, Colorado. Neutron flux monitor Fish Canyon Tuff sanidine (FC-2). Assigned age = 28.201 Ma (Kuiper et al., 2008).

Instrumentation: Total fusion monitor analyses performed on a Argus VI mass spectrometer on line with automated all-metal extraction system. System = JanStep-heat analyses performed on a Argus VI mass spectrometer on line with automated all-metal extraction system. System = ObamaMulti-collector configuration: 40Ar-H1, 39Ar-Ax, 38Ar-L1, 37Ar-L2, 36Ar-CDDFlux monitors and sample fused with a Photon Machines Inc. CO2 laser.

Analytical parameters: Sensitivity for the Argus VI with the Diode laser (step-heated samples) is 9.84e-17 moles/fA. Sensitivty for the Argus VI with the CO2 laser (fused monitors)is 4.62 e-17 moles/fA. Typical system blank and background was 49.9, 0.92, 0.0.83, .092, 0.18 x 10-18 moles at masses 40, 39, 38, 37 and 36, respectively for the laser analyses.J-factors determined by CO2 laser-fusion of 6 single crystals from each of 13 radial positions around the irradiation tray. Decay constants and isotopic abundances after Minn et al., (2000).

Table 2. 40Ar/39Ar analytical data.ID 40Ar/39Ar 37Ar/39Ar 36Ar/39Ar 39ArK K/Ca 40Ar* Age ±1σ

(x 10-3) (x 10-15 mol) (%) (Ma) (Ma)

CAF2-36362, san, J=0.0038914±0.02%, D=1±0, NM-276F, Lab#=6368501 2.525 0.0158 0.0740 8.724 32.3 98.9 17.70 0.0110 2.524 0.0187 0.0618 5.724 27.2 99.0 17.70 0.0109 2.519 0.0181 0.0509 7.008 28.2 99.1 17.71 0.0108 2.522 0.0157 0.0570 7.144 32.4 99.1 17.71 0.0106 2.515 0.0162 0.0334 5.571 31.5 99.3 17.71 0.0105 2.521 0.0152 0.0500 5.353 33.6 99.1 17.71 0.0113 2.516 0.0156 0.0248 14.572 32.6 99.4 17.72 0.0002 2.526 0.0134 0.0606 9.838 38.2 99.0 17.73 0.0103 2.520 0.0229 0.0419 7.589 22.3 99.3 17.73 0.0112 2.583 0.0148 0.2445 9.106 34.4 96.9 17.73 0.0111 2.517 0.0138 0.0221 7.883 37.0 99.5 17.74 0.0104 2.527 0.0154 0.0605 6.034 33.1 99.0 17.74 0.0107 2.596 0.0209 0.2688 3.777 24.4 96.7 17.79 0.01Mean age ± 2σ n=12 MSWD=3.51 31.9 ±8.6 17.72 0.01

Notes:Isotopic ratios corrected for blank, radioactive decay, and mass discrimination, not corrected for interfering reactions.Errors quoted for individual analyses include analytical error only, without interfering reaction or J uncertainties.Mean age is weighted mean age of Taylor (1982). Mean age error is weighted error of the mean (Taylor, 1982), multiplied by the root of the MSWD where MSWD>1, and also incorporates uncertainty in J factors and irradiation correction uncertainties.Decay constants and isotopic abundances after Steiger and Jäger (1977).# symbol preceding sample ID denotes analyses excluded from mean age calculations.Ages calculated relative to FC-2 Fish Canyon Tuff sanidine interlaboratory standard at 28.201 Ma Decay Constant (LambdaK (total)) = 5.543e-10/aCorrection factors: (39Ar/37Ar)Ca = 0.0007064 ± 4e-06 (36Ar/37Ar)Ca = 0.0002731 ± 0 (38Ar/39Ar)K = 0.01261 (40Ar/39Ar)K = 0.00808 ± 0.00041

CAF2-36362 Sanidine

0

0.5

1.0

1.5

2.0

9698

100

102104

25

30

35

40

17.2 17.4 17.6 17.8 18.0

17.72 ± 0.01 Ma, MSWD = 3.51

Age (Ma)

Rel

ativ

e Pr

obab

ility

% R

adio

geni

c

K/C

a

Moles 39A

r(x 10 -14)