Laboratory Equipment and Analytical Techniques
 The Nevada Isotope Geochronology Laboratory will house two rare gas mass spectrometers, a MAP215-50 and Nuclide 4.5-60-RSS. The MAP 215-50, its extraction line, and auxiliary equipment will be fully computer automated using LabView software. The MAP is a modern high sensitivity, low background machine featuring a triple collector assembly with Faraday cup, standard electron multiplier, and quiet electron multiplier with pulse counting electronics. This mass spectrometer will be connected to a high vacuum extraction line with automated pneumatic valves, a 4K cryogenic pump for condensing water vapor or separating noble gases, and a quadrapole mass spectrometer for monitoring gas species prior to admission to the rare gas mass spectrometer. Sample manipulation will be accomplished by an automated x-y stage with up to 221 individual samples for laser analysis, or a motorized furnace sample dropper capable of running up to 15 sequential samples. Sample heating can be accomplished by a double vacuum resistance furnace capable of heating samples to 1600 °C ± 1-2 °C, or a Merchantek laser system consisting of a 20W CO2 laser, or an ultraviolet laser capable of 5-10 µm resolution. The old Nuclide will be operated manually, at least initially, and will accomplish sample heating using a custom built furnace similar to that installed on the MAP's line. The Nuclide will be utilized for running older (e.g., Mesozoic-Paleozoic or older) samples which do not require the performance of the more sensitive MAP.
We will eventually offer three isotopic dating techniques; the 40Ar/39Ar method (a variant of the conventional K/Ar method) and the 21Ne and 3He surface exposure dating method. The 40Ar/39Ar dating method has a wide range of uses in geochronology (defining eruption or emplacement ages of igneous rocks with applications in, for example, volcanic hazards assessment, ore genesis, and ages of hominid fossils) and thermochronology (constraining time-temperature histories of crustal rocks, for example, timing and rates of crustal-scale tectonic events such as uplift of the Himalayas, and subsidence of sedimentary basins with implications for petroleum genesis). The generation of cosmic ray induced isotopes such as 21Ne and 3He in rocks exposed at the Earth's surface has recently opened new areas of geologic research, most notably in dating very young or recently exposed rocks not amenable to other dating methods. Surface exposure dating has been applied to research aimed at understanding climate change, development of landforms, constraining erosion rates, and nuclear waste site assessment, and is a rapidly growing and exciting new field in geochronology. The combination of these isotopic dating techniques in a single laboratory will permit visitors, faculty, and students to conduct research on a large variety of problems in geoscience involving materials spanning the entire range of geologic time. 40Ar/39Ar analyses are expected to be available during Spring of 1999 with the cosmogenic exposure dating techniques coming in during Summer of 1999. |
