40 Ar (10-14 mol) 40 Ar* %

Transcription

1 Appendix 1: Complete 40 Ar/ 39 Ar incremental heating results Adak Canyon Dive 099 Sample: J99S20S24 Material: groundmass weight = 2.1 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: UW40D2 Rock type: basalt 0.75 > ± > ± > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 1.76 isochron age: ± 3.54 total fusion age: ± 2.29 Sample: J99S20S24 Material: groundmass weight = 3.8 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: UW40D2b Rock type: basalt 0.75 > ± > ± > ± > ± > ± > ± 6.50 weighted mean plateau age: ± 0.87 isochron age: ± 1.30 total fusion age: ± 0.95 Sample: J99S13S19 Material: groundmass weight = 4.0 mg μ = ± 0.05% (1σ) J = ± 0.15% (1σ) Experiment: UW40E3d Rock type: gabbro 1.00 > ± > ± > ± > ± > ± 1.16 weighted mean plateau age: ± 0.43 isochron age: ± 0.55 total fusion age: ± 1.30 Sample: J99S12S18 Material: groundmass weight = 3.7 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: D6 Rock type: andesite 1.25 > ± > ± > ± > ± > ± > ± > ± > ± ± 2.80 weighted mean plateau age: ± 0.23 isochron age: ± 0.29 total fusion age: ± 0.24 Sample: J99S6S9 Material: groundmass weight = 1.4 mg μ = ± 0.05% (1σ) J = ± 0.20% (1σ) Experiment: UW40B5 Rock type: basalt 0.75 > ± > ± > ± > ± 3.67 weighted mean plateau age: ± 0.41 isochron age: ± 1.74 total fusion age: ± 0.55 Sample: J99S6S9 Material: groundmass weight = 2.0 mg μ = ± 0.05% (1σ) J = ± 0.20% (1σ) Experiment: UW40B5c Rock type: basalt 1.00 > ± > ± > ± > ± > ± > ± > ± 8.77 weighted mean plateau age: ± 0.55 isochron age: ± 0.91 total fusion age: ± 0.60 Sample: J99S6S9 Material: groundmass weight = 0.7 mg μ = ± 0.05% (1σ) J = ± 0.20% (1σ) Experiment: UW40B5d Rock type: basalt 0.75 > ± > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 0.92 isochron age: ± 1.71 total fusion age: ± 1.14

2 Sample: J99S4S7 Material: groundmass weight = 2.1 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: UW40D4 Rock type: basaltic andesite 0.75 > ± > ± > ± > ± > ± > ± > ± 4.83 weighted mean plateau age: ± 0.33 isochron age: ± 0.48 total fusion age: ± 0.40 Sample: J99S3S6 Material: plagioclase weight = 2.1 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: UW40B3e Rock type: basalt 0.88 > ± > ± > ± > ± > ± > ± > ± > ± > ± 1.40 weighted mean plateau age: ± 0.41 isochron age: ± 1.97 total fusion age: ± 0.44 Sample: J99S3S6 Material: plagioclase weight = 2.7 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: UW40B4e Rock type: basalt 1.75 > ± > ± > ± > ± > ± > ± 0.22 weighted mean plateau age: ± 0.19 isochron age: ± 2.57 total fusion age: ± 0.20 Sample: J99S3S5 Material: groundmass weight = 2.2 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: UW40D5 Rock type: basalt 1.00 > ± > ± > ± > ± > ± > ± 7.69 weighted mean plateau age: ± 0.48 isochron age: ± 0.61 total fusion age: ± 0.58 Sample: J99S2S4 Material: groundmass weight = 1.4 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: UW40B2 Rock type: volcaniclastic andesite 1.25 > ± > ± > ± > ± > ± > ± > ± 5.00 weighted mean plateau age: ± 0.48 isochron age: ± 1.12 total fusion age: ± 0.50 Sample: J99S2S4 Material: groundmass weight = 0.7 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: UW40B2c Rock type: volcaniclastic andesite 0.75 > ± > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 0.95 isochron age: ± 1.69 total fusion age: ± 1.10 Sample: J99S1S2 Material: groundmass weight = 1.4 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: UW40B6 Rock type: basaltic andesite 0.75 > ± > ± > ± > ± > ± > ± 1.17 weighted mean plateau age: ± 0.61 isochron age: ± 1.26 total fusion age: ± 0.73

3 Sample: J99S1S2 Material: groundmass weight = 0.7 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: UW40B6c Rock type: basaltic andesite 0.75 > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 1.63 isochron age: ± 3.32 total fusion age: ± 1.83 Sample: J99S1S1 Material: groundmass weight = 1.6 mg μ = ± 0.05% (1σ) J = ± 0.15% (1σ) Experiment: J99S1S1 Rock type: volcaniclastic andesite 1.25 > ± > ± > ± > ± > ± > ± > ± > ± 2.53 weighted mean plateau age: ± 0.27 isochron age: ± 0.86 total fusion age: ± 0.32 Adak Canyon Dive 098 Sample: J98S7S8 Material: groundmass weight = 2.1 mg μ = ± 0.05% (1σ) J = ± 0.15% (1σ) Experiment: UW40C4e Rock type: basaltic andesite 0.75 > ± > ± > ± > ± > ± > ± > ± ± 0.35 weighted mean plateau age: ± 0.18 isochron age: ± 0.20 total fusion age: ± 0.25 Sample: J98S7S8 Material: groundmass weight = 1.4 mg μ = ± 0.05% (1σ) J = ± 0.15% (1σ) Experiment: UW40C4f Rock type: basaltic andesite ± ± > ± > ± > ± > ± > ± > ± > ± > ± 3.51 weighted mean plateau age: ± 0.33 isochron age: ± 0.69 total fusion age: ± 0.36 Sample: J98S6S7 Material: groundmass weight = 1.2 mg μ = ± 0.05% (1σ) J = ± 0.15% (1σ) Experiment: UW40C6 Rock type: andesite 1.25 > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 0.38 isochron age: ± 0.78 total fusion age: ± 0.47 Sample: J98S6S7 Material: groundmass weight = 1.5 mg μ = ± 0.05% (1σ) J = ± 0.15% (1σ) Experiment: UW40C6b Rock type: andesite 0.75 > ± > ± > ± > ± > ± > ± > ± > ± 1.10 weighted mean plateau age: ± 0.41 isochron age: ± 0.70 total fusion age: ± 0.46

4 Sample: J98S3S3 Material: groundmass weight = 2.0 mg μ = ± 0.05% (1σ) J = ± 0.15% (1σ) Experiment: UW40E2 Rock type: basaltic andesite 0.75 > ± > ± > ± > ± > ± > ± > ± > ± 6.06 weighted mean plateau age: ± 1.08 isochron age: ± 1.15 total fusion age: ± 1.44 Murray Canyon Dredge Sample: TN Material: plagioclase weight = 2.0 mg μ = ± 0.03% (1σ) J = ± 0.21% (1σ) Experiment: UW53A1 Rock type: gabbro 3.00 > ± > ± > ± > ± > ± > ± > ± > ± > ± > ± 5.97 weighted mean plateau age: ± 0.62 isochron age: ± 0.78 total fusion age: ± 0.88 Sample: TN Material: biotite weight = 1.2 mg μ = ± 0.03% (1σ) J = ± 0.22% (1σ) Experiment: UW53A2 Rock type: gabbro 3.50 > ± > ± > ± > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 0.88 isochron age: ± 1.28 total fusion age: ± 1.03 Sample: TN Material: groundmass weight = 1.8 mg μ = ± 0.03% (1σ) J = ± 0.26% (1σ) Experiment: UW53A5 Rock type: basalt ± > ± > ± > ± > ± > ± > ± > ± > ± ± 3.73 weighted mean plateau age: ± 0.67 isochron age: ± 1.16 total fusion age: ± 0.95 Sample: TN Material: groundmass weight = 1.5 mg μ = ± 0.03% (1σ) J = ± 0.26% (1σ) Experiment: UW53A5b Rock type: basalt ± ± ± > ± > ± > ± > ± > ± > ± > ± > ± 6.12 weighted mean plateau age: ± 0.70 isochron age: ± 1.99 total fusion age: ± 0.69 Sample: TN Material: groundmass weight = 2.5 mg μ = ± 0.03% (1σ) J = ± 0.26% (1σ) Experiment: UW53A5c Rock type: basalt ± ± > ± > ± > ± > ± > ± > ± > ± 4.54 weighted mean plateau age: ± 0.71 isochron age: ± 2.56 total fusion age: ± 0.74

5 Terrestrial volcanic and plutonic rocks Sample: AD Material: groundmass weight = 1.0 mg μ = ± 0.09% (1σ) J = ± 0.15% (1σ) Experiment: UW49A4 Rock type: andesite 0.63 > ± > ± > ± > ± > ± > ± > ± 7.00 weighted mean plateau age: 7.06 ± 0.19 isochron age: 7.00 ± 0.24 total fusion age: 7.10 ± 0.25 Sample: AD Material: plagioclase weight = 1.4 mg μ = ± 0.09% (1σ) J = ± 0.15% (1σ) Experiment: UW49A5b Rock type: andesite 2.50 > ± > ± > ± > ± > ± > ± > ± ± 2.98 weighted mean plateau age: 7.85 ± 1.79 isochron age: 7.90 ± 3.17 total fusion age: ± 1.79 Sample: KAG7-32 Material: biotite weight = 0.4 mg μ = ± 0.05% (1σ) J = ± 0.19% (1σ) Experiment: UW40H2 Rock type: granodiorite 0.88 > ± > ± > ± > ± > ± > ± > ± > ± > ± 0.16 weighted mean plateau age: ± 0.11 isochron age: ± 0.12 total fusion age: ± 0.14 Sample: KAG7-50 Material: biotite weight = 1.5 mg μ = ± 0.05% (1σ) J = ± 0.19% (1σ) Experiment: UW40G2b Rock type: granodiorite 0.83 > ± > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 0.52 isochron age: ± 0.71 total fusion age: ± 0.55 Sample: KAG7-50 Material: hornblende weight = 1.4 mg μ = ± 0.05% (1σ) J = ± 0.19% (1σ) Experiment: UW40G3 Rock type: granodiorite ± > ± > ± > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 0.92 isochron age: ± 1.67 total fusion age: ± 1.09 Sample: AM33 Material: plagioclase weight = 1.5 mg μ = ± 0.05% (1σ) J = ± 0.16% (1σ) Experiment: UW40I2 Rock type: granodiorite 0.88 > ± > ± > ± > ± > ± 7.16 weighted mean plateau age: ± 0.67 isochron age: ± 1.22 total fusion age: ± 0.83

6 Sample: AM33 Material: hornblende weight = 1.0 mg μ = ± 0.05% (1σ) J = ± 0.16% (1σ) Experiment: UW40I3 Rock type: granodiorite 1.00 > ± > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 0.96 isochron age: ± 1.40 total fusion age: ± 1.30 Sample: MR80-12 Material: groundmass weight = 2.0 mg μ = ± 0.09% (1σ) J = ± 0.16% (1σ) Experiment: UW49B1 Rock type: basalt 0.63 > ± > ± > ± > ± > ± > ± > ± 5.91 weighted mean plateau age: ± 0.35 isochron age: ± 0.69 total fusion age: ± 0.44 Sample: AT80-87 Material: plagioclase weight = 2.3 mg μ = ± 0.05% (1σ) J = ± 0.15% (1σ) Experiment: UW40E6 Rock type: gabbro 0.75 > ± > ± > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 1.36 isochron age: ± 2.20 total fusion age: ± 1.78 Sample: AT80-87 Material: plagioclase weight = 3.6 mg μ = ± 0.05% (1σ) J = ± 0.15% (1σ) Experiment: UW40E6b Rock type: gabbro 0.75 > ± > ± > ± > ± > ± ± ± ± 5.61 weighted mean plateau age: ± 1.04 isochron age: ± 2.47 total fusion age: ± 1.40 Sample: SED-AB Material: hornblende weight = 1.5 mg μ = ± 0.05% (1σ) J = ± 0.16% (1σ) Experiment: UW40I4 Rock type: granodiorite 0.98 > ± > ± > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 0.81 isochron age: ± 1.06 total fusion age: ± 1.36 Sample: SED-AB Material: hornblende weight = 3.0 mg μ = ± 0.05% (1σ) J = ± 0.16% (1σ) Experiment: UW40I4b Rock type: granodiorite 1.13 > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 1.54 isochron age: ± 1.89 total fusion age: ± 2.35

7 Sample: SED-36-D Material: biotite weight = 0.7 mg μ = ± 0.05% (1σ) J = ± 0.22% (1σ) Experiment: UW40K2 Rock type: granodiorite ± > ± > ± > ± > ± > ± > ± > ± > ± 1.39 weighted mean plateau age: ± 0.19 isochron age: ± 0.24 total fusion age: ± 0.23 Sample: HB Material: biotite weight = 0.5 mg μ = ± 0.05% (1σ) J = ± 0.28% (1σ) Experiment: UW40F3 Rock type: granodiorite ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 0.27 isochron age: ± 0.30 total fusion age: ± 0.28 Sample: HB Material: biotite weight = 0.6 mg μ = ± 0.05% (1σ) J = ± 0.28% (1σ) Experiment: UW40F3 Rock type: granodiorite 0.88 > ± > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 0.60 isochron age: ± 0.64 total fusion age: ± 0.80 Sample: HB Material: hornblende weight = 0.2 mg μ = ± 0.05% (1σ) J = ± 0.28% (1σ) Experiment: UW40F4 Rock type: granodiorite 0.93 > ± > ± > ± > ± > ± > ± > ± 3.29 weighted mean plateau age: ± 0.81 isochron age: ± 1.10 total fusion age: ± 1.11 Sample: HB Material: hornblende weight = 0.5 mg μ = ± 0.05% (1σ) J = ± 0.28% (1σ) Experiment: UW40F4b Rock type: granodiorite 1.00 > ± > ± > ± > ± > ± > ± > ± > ± > ± 3.24 weighted mean plateau age: ± 1.51 isochron age: ± 2.09 total fusion age: ± 1.59 Sample: AT80-22 Material: plagioclase weight = 2.0 mg μ = ± 0.05% (1σ) J = ± 0.19% (1σ) Experiment: UW40H5 Rock type: gabbro 0.88 > ± > ± > ± > ± > ± > ± > ± > ± ± weighted mean plateau age: ± 0.44 isochron age: ± 0.99 total fusion age: ± 0.63 Sample: AT80-22 Material: hornblende weight = 0.3 mg μ = ± 0.05% (1σ) J = ± 0.19% (1σ) Experiment: UW40H6 Rock type: gabbro 1.00 > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 2.17 isochron age: ± 3.13 total fusion age: ± 2.40

8 Sample: AT80-22 Material: hornblende weight = 0.3 mg μ = ± 0.05% (1σ) J = ± 0.19% (1σ) Experiment: UW40H6 Rock type: gabbro 0.98 > ± > ± > ± > ± > ± > ± > ± weighted mean plateau age: ± 2.65 isochron age: ± 3.23 total fusion age: ± 2.82 Sample: BW8-R39B Material: groundmass weight = 2.5 mg μ = ± 0.09% (1σ) J = ± 0.16% (1σ) Experiment: UW49B3 Rock type: basalt 0.63 > ± > ± > ± > ± > ± > ± > ± 2.10 weighted mean plateau age: ± 0.50 isochron age: ± 0.74 total fusion age: ± 0.50 Sample: MV80-24 Material: plagioclase weight = 3.0 mg μ = ± 0.09% (1σ) J = ± 0.16% (1σ) Experiment: UW49A6 Rock type: basalt 0.75 > ± > ± > ± > ± > ± > ± > ± ± 6.92 weighted mean plateau age: ± 0.93 isochron age: ± 1.50 total fusion age: ± 1.03 Sample: MV80-24 Material: plagioclase weight = 4.0 mg μ = ± 0.09% (1σ) J = ± 0.16% (1σ) Experiment: UW49A6b Rock type: basalt 0.63 > ± > ± > ± > ± > ± > ± > ± 2.65 weighted mean plateau age: ± 0.63 isochron age: ± 1.69 total fusion age: ± 0.79 Sample: FB8-19 Material: biotite weight = 0.3 mg μ = ± 0.05% (1σ) J = ± 0.16% (1σ) Experiment: UW40I5 Rock type: gabbro 0.88 > ± > ± > ± > ± > ± > ± > ± > ± > ± 0.98 weighted mean plateau age: ± 0.22 isochron age: ± 0.23 total fusion age: ± 0.23 a Corrected for 37 Ar and 39 Ar decay, half-lives of 35.1 days and 269 years, respectively. b Ages calculated relative to Ma Taylo Creek Rhyolite sanidine (Renne et al., 1998); using the decay constants of Steiger and Jäger (1977); uncertainties reported at 2σ precision. > indicates incremental heating steps that comprise a plateau

9 THE FOLLOWING DOCUMENT AND TABLE ARE TO BE INCLUDED IN AN ELECTRONIC SUPPLEMENT ANALYTICAL METHODS 40 Ar/ 39 Ar Geochronology Groundmass, plagioclase, amphibole, and biotite separates were prepared from volcanic and plutonic samples by crushing, sieving to mm, magnetic sorting, density separation, air abrasion, and hand picking under a binocular microscope. The purified separates were weighed and placed into 2.5 cm diameter Al disks with Ma sanidine from the Taylor Creek rhyolite (Renne et al., 1998) as a neutron fluence monitor. The Al disks were irradiated for either 10 or 20 hours at the Oregon State University Triga reactor in the Cadmium-Lined In-Core Irradiation Tube (CLICIT) where they received fast neutron doses of 1 to 2 x n/cm 2. At the University of Wisconsin Rare Gas Geochronology Laboratory, mg of the purified separates were incrementally heated using a 25-Watt CO 2 laser attached to a 250 cm 3 gas cleanup line and mass spectrometer. Gas extraction, measurement, and data reduction followed the procedures of Singer et al. (2004). Mass discrimination was monitored using an automated air pipette and varied between ± and ± per atomic mass unit during the analytical periods. Experiments yielded largely concordant age spectra with 5-10 steps comprising > 80% of the gas released. Plateau steps were regressed to calculate isochrons (York, 1969) and indicate that effects of low temperature alteration or excess argon are not significant in any sample. The isochrons give our preferred ages. All ages were calculated using the decay constants of Steiger and Jäger (1977) and are reported with ± 2 uncertainties. K-Ar ages mentioned throughout the text that were obtained prior to 1977 have been recalculated using the decay constants of Steiger and Jäger (1977). Major and trace elements Whole rock major and trace element compositions were measured by ICP-MS techniques at the GeoAnalytical Laboratory at Washington State University. Prior to analysis, samples were prepared into fused beads at the University of South Carolina. First, the samples were powdered in an agate ball mill. Two grams of powder was then mixed with an equal amount of lithium tetraborate flux, placed into a graphite crucible, and fused in a 1000 o muffle furnace for 30 minutes. The resulting bead was ground again, then dissolved on a hotplate using a HF-HNO 3 - HClO 4 mixture in an open teflon vial. The sample was evaporated to dryness, followed by additional evaporation in 2 ml of HClO 4. All samples were diluted to 60ml and analyzed along with three in-house rock standards using a Thermo-Finnigan ICP-MS. REFERENCES Renne, P.R., Swisher, C.C., Deino, A.L., Karner, D.B., Owens, T.L., and DePaolo, D.J., 1998, Intercalibration of standards, absolute ages, and uncertainties in 40 Ar/ 39 Ar dating: Chemical Geology, v. 145, p Singer, B.S., Ackert, R.P., and Guillou, H., 2004, 40 Ar/ 39 Ar and K-Ar chronology of Pleistocene glaciations in Patagonia: Geological Society of America Bulletin, v. 116, p Steiger, R.H., and Jäger, E., 1977, Subcommission on geochronology; convention on the use of decay constants in geo- and cosmochronology: Earth and Planetary Science Letters, v. 36, p