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Surface Exposure Dating Using Cosmogenic 3He and 21Ne

3He and 21Ne produced in situ in surface rocks provide a chronometer for surface processes, complementing radioactive in situ cosmognenic nuclides like 10Be, 36Cl, and 26Al. Several areas of the Pacific Northwest are interesting targets for exposure dating using these techniques, including the Yellowstone region, the Steens Mountain area of eastern Oregon (a high mountain range with a well preserved, but largely undated, glacial moraine sequence composed primarily of basalt boulders), and the Columbia River Plateau. Debris flows, and deposits related to outburst floods during the end stages of glaciation are also of interest. Another area we plan to explore is application of cosmogenic noble gas measurements to mineral phases found in granitic rocks, which dominate many formerly glaciated regions of the world. Quartz appears to quantitatively retain 21Ne under most conditions. Amphibole, garnet, mica and fluorapatite have been suggested as phases that may retain cosmogenic noble gases well. Iron oxide minerals may also be useful. Other minerals may also be suitable, but a challenge with many is that they can be enriched in uranium and/or thorium and therefore in radiogenic 4He, requiring measurements of small quantities of cosmogenic 3He in the presence of large abundances of 4He. At OSU we have a large library of samples of granite, gneiss, quartzite, and other rocks from a variety of locations (Norway, Labrador, eastern Europe, Canadian Shield, Svalbard, Greenland, western US, many of which have cosmogenic 10Be measurements, and these will provide excellent suites to explore the utility of noble gas measurements in other mineral phases.