Earth system scientists increasingly explore research frontiers that require precise timing of physical, chemical and biological processes. With the precise and accurate measurement of geological ages they are able to correlate and link past events in the Earth's geological record and determine durations and rates at which processes act. The application of 40Ar/39Ar age dating techniques is especially critical to addressing many of the grand scientific challenges in hotspot geodynamics, large-scale cataclysmic volcanism, paleo-environmental impacts, lunar crust formation and geological time scale calibrations. The acquisition of a state-of-the-art ARGUS VI multi-collector noble gas mass spectrometer to the 40Ar/39Ar Geochronology Laboratory at the College of Oceanic & Atmospheric Sciences at Oregon State University is significantly improving the capability to conduct 40Ar/39Ar experiments on very small samples from dredged submarine basalts and deep sea drill cores, fine-grained terrigenous sediment fractions to use as paleoproxies to study sediment transport and climate change, extremely small fragments of lunar impact melts and breccias, and low-potassium lavas from large oceanic igneous provinces in order to unravel their temporal evolution and their world-wide environmental impacts.
The Oregon State University 40Ar/39Ar Geochronology Laboratory has been in operation since 1977 and functions as a multi-user facility for both scientists and students, within and outside the United States. With more than 75 visitors and students over the last 17 years, 70 collaborators over the last 3 years, and more than 175 publications, this NSF-sponsored laboratory has established itself as a widely-used facility, specifically focused on the geochronology of ocean crust, seamounts, marine sediments and large igneous provinces. The new ARGUS VI mass spectrometer will operate in tandem with the current MAP 215-50 mass spectrometer and will allow for a continued active participation of undergraduate and graduate students and post-doctoral fellows in this laboratory, training them in noble gas analytical techniques and the use of the NSF-sponsored ArArCALC software.
K/Ar and 40Ar/39Ar geochronology has had a profound impact on the Earth system sciences since its introduction in 1965. In the Argon Geochronology Laboratory at Oregon State University (OSU) we have been employing these dating methods ever since 1977 with a focus on volcanism in both the marine and terrestrial environment to improve the geochronology of the ocean crust, ocean island volcanism, large igneous provinces, lunar and planetary rocks, hydrothermal minerals and clays, and much more. With this NSF grant from EAR Instrumentation and Facilities we have successfully installed an ARGUS-VI multi-collector mass spectrometer for 40Ar/39Ar geochronology, a ~500cc ultra-high vacuum (low blank) extraction line for cleaning of argon gas samples, and a CO2 laser with laser scanning head for releasing the argon gas from geological materials. In September 2013 the first ARGUS-VI became fully operational. Since then, we have carried out 38,857 measurements of individual gas samples (including single incremental heating steps, total fusions of single crystals, blanks or backgrounds, air shots or collector calibrations). Our lab's productitiy is now 5x higher than what was typical for our old MAP215-50 mass spectrometer, which is now retired. These measurements comprise 653 incremental heating experiments (with 20 to 40 incremental heating steps, not counting blanks), 356 airshot experiments, 358 collector calibration experiments and 33 flux monitor experiments. After being in production for more than one year with the ARGUS-VI the major outcomes of this grant are: (1) We are operational 24/7 and more efficient with a 5x higher productivity. (2) Our precision (and accuracy) is an order of magnitude improved compared to the MAP215-50. (3) Based on our succes story with the ARGUS-VI we could retire the MAP215-50 and replace it with a second ARGUS-VI (arriving December 2014 and likely operational in the spring of 2015) using support from CEOAS, OSU Research Office and the Vetlesen Foundation. We expect productivity to raise even higher to 9x MAP215-50 levels, while our capabilities will be expanded in particular toward dating on the younger end of the timescale. (4) The youngest ages measured so far are 12,000 ± 400 years (2σ) on sanidines. (5) We regularly are measuring low- to medium-K basaltic rocks about 100-500 ka in age with uncertainties smaller than 5,000 years (2σ).
