Geochemical and 40Ar/39Ar Analytical Data of Rocks from Glacier Bay National Park and Preserve

The geochemical analyses, run at ALS Global laboratories (Fairbanks, Alaska, and North Vancouver, British Columbia), includes quality control steps through sample preparation and analysis, inter-laboratory test programs, and regular internal audits. Samples were run with standard reference materials and blanks. Quality control data is archived at ALS. For the argon-argon geochronology analyses, mineral samples were irradiated with monitor mineral MMhb-1 with preferred age of 523.5 Ma (Renne et al, 1994). Samples and monitors were step-heated or fused using a 6-watt argon-ion laser. Argon purification was achieved using a liquid nitrogen cold trap and SAES Zr-Al getter at 400 degrees C. The argon isotopes were measured and corrected for system blank and mass discrimination, as well as neutron induced reactions on calcium, potassium and chlorine. Typical full-system 8 min laser blank values (in moles) were generally 2e-16 mol 40Ar, 3e-18 mol 39Ar, 9e-18 mol 38Ar, 2e-18 mol 37Ar, and 2e-18 mol 36Ar, which are 10-50 times smaller than the sample/standard volume fractions. Correction factors for nucleogenic interferences during irradiation were determined from irradiated CaF2 and K2SO4 as follows: (39Ar/37Ar)Ca = 7.06e-4, (36Ar/37Ar)Ca = 2.79e-4, and (40Ar/39Ar)K = 0.0297. Mass discrimination was monitored by analyzing air shots with an assumed 40Ar/36Ar value of 295.5 (Nier, 1950). The mass discrimination during these experiments was 1.3% per mass unit. No significant variation in discrimination over the course of the analyses was measured and so a single value was used in data reduction. Ages with +/- 1 sigma error were calculated using the decay constants of Renne et al, 2010. The integrated age is the age given by the total gas measured and is equivalent to a potassium-argon (K-Ar) age. A plateau age is reported if three or more consecutive gas fractions representing at least 50 percent of the total gas released that are within two standard deviations of each other and with an overall Mean Square Weighted Deviation (MSWD) less than or equal to 2.5.