Revised astronomically calibrated 40Ar/39Ar ages for the Fish Canyon Tuff sanidine – Closing the interlaboratory gap
نویسندگان
چکیده
The 40Ar/39Ar geochronology method is capable of high precision (<0.05%), but remains limited by relatively large uncertainties in 40K decay constants and the ages natural reference mineral standards. most widely used well-known ca. 28 Ma Fish Canyon Tuff sanidine (FCTs). Several studies have attempted to calibrate FCTs against astronomically tuned tephra Crete (Faneromeni A1 tephra) Morocco (Messâdit Mes4 tuff) as well deep-sea sedimentary sequences. Previously reported range from 28.126 ± 0.019 28.21 0.18 (2σ), a ~0.3%, compared levels <0.05% achievable new generation, multi-collector mass spectrometer systems. In this study, we revisit astronomical calibration FCTs. Relative 6.943 0.005 for tuff (A1Ts) 6.791 0.010 (2σ) (Mes4Ts), calculate revised 28.175 0.012 (±0.023 Ma, including uncertainty age A1Ts) 28.176 (±0.042 Mes4Ts), respectively (assuming negligible differential 39Ar recoil loss). This within recent intercalibrations, permitting calculation inter-laboratory mean (±0.023) 28.179 0.009 (±0.042) respectively. As more precise than that tuff, recommend former value adopted consistent with available U-Pb zircon data, distinctly older 28.10 28.150 inferred Ocean Drilling Program sediments, indicating further work required align tuning terrestrial versus sediments. Based on previous R-values Alder Creek Rhyolite (ACRs) Mount Dromedary biotite (MD-2b) minerals, co-irradiated FCTs, calibrated 1.18342 0.00069 (±0.009) ACRs 99.323 0.077 (±0.33) MD-2b, latter amended 99.20 0.01 (±0.38) account relative loss 39ArK. To enhance accuracy ages, our study also highlights need carefully control neutron fluence gradients consider effects.
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ژورنال
عنوان ژورنال: Chemical Geology
سال: 2022
ISSN: ['0009-2541', '1872-6836']
DOI: https://doi.org/10.1016/j.chemgeo.2022.120815