Bascom ARgon Dating (BARD) Laboratory
Welcome to the Bascom ARgon Dating (BARD) Laboratory webpage.
In the Bascom ARgon Dating (BARD) Laboratory, we use community standard methods for 40Ar/39Ar isotopic analysis of potassium-bearing minerals and glasses. The 40Ar/39Ar isotopic system allows for age determination of potassium-bearing phases over ~104-109 yr timescales, spanning most of geologic time. Thus, 40Ar/39Ar geochronology is an indispensable tool in documenting rock histories in support of USGS mission critical goals in geologic mapping, geologic hazards, energy, and minerals research. The BARD Lab utilizes a tailored approach, including optical and electron petrography, geochemical modeling, X-ray diffraction (XRD), Raman spectroscopy and other methods to understand the petrologic context of dated minerals. This work is commonly done in close collaboration with USGS geologic field mappers and in direct support of USGS-National Cooperative Geologic Mapping (NCGMP) projects.
Research and Expertise
Lab staff conduct research that places time constraints on geologic units and processes. A major component of our work focuses on poly-deformed igneous and metamorphic rocks of the Appalachian Mountains, but we also work globally. Most of this geochronologic research emphasizes detailed sample characterization as a key to understanding the geologic implications of radiogenic isotope measurements. We apply our expertise in mineralogy, microtexture, and metamorphic petrology, along with a variety of tools (see associated facilities), to assess isotopic data collected in the BARD Lab and other laboratories.
Lab staff also conduct research on active tectonics, landscape evolution, and tectonic geomorphology. We apply our expertise in detrital geochronology by the 40Ar/39Ar and U/Pb methods, low temperature thermochronology by the 40Ar/39Ar and U-Th/He methods, and more recently cosmogenic nuclide dating. The Reston Cosmogenic Nuclide (RECON) Lab, started in 2021, shares workspace and staff with the BARD Lab.
Facilities
Argon Geochronology
- VG1200 single collector noble gas mass spectrometer
- NGX electronics (new 2022)
- Resistance furnace
- 30W Synrad CO2 laser (new 2022)
- Diode-laser microfurnace (under construction)
- Operating under NGX software
- MAP216 single collector noble gas mass spectrometer
- Resistance furnace
- 50W Synrad CO2 laser
- Resistance furnace
- Operating under MassSpec software
Mineral separation equipment
- Frantz L1 magnetic separators
- Fume hoods
- Organic and inorganic heavy liquids, acids
- Sturtevant jaw crusher, Bico disk mill, Wilfley table, rock saws
- Binocular and petrographic microscopes
- Diamond wire saw
- Mendenbach microdrill
- Good attitudes
- Struers automated polisher
- Sartorius microbalance
Publications
Photoluminescence imaging of whole zircon grains on a petrographic microscope—An underused aide for geochronologic studies
The refractory nature of zircon to temperature and pressure allows even a single zircon grain to preserve a rich history of magmatic, metamorphic, and hydrothermal processes. Isotopic dating of micro-domains exposed in cross-sections of zircon grains allows us to interrogate this history. Unfortunately, our ability to select the zircon grains in a heavy mineral concentrate that records the most ge
40Ar/39Ar and U-Pb SIMS zircon ages of Ediacaran dikes from the Arabian-Nubian Shield of south Jordan
A spectacular feature of the Arabian-Nubian Shield (ANS) is the abundance of well-exposed and extensive Neoproterozoic dike swarms of multiple generations. These dikes are generally categorized into metamorphosed and unmetamorphosed post-orogenic dike swarms. The unmetamorphosed dikes in the northern ANS can be grouped into an old and young generations. We dated three dikes from the old generation