9523565 de Silva Recently an important contribution to the field of geomorphology has been the development of a nuclear method for quantifying erosion rates and exposure ages of geological surfaces. the method relies on measurement of a number of radionuclides and stable nuclides which are continually being produced in situ in rocks exposed to cosmic rays. We have chosen to examine 36Cl due to its ease of measurement and applicability to volcanic rocks. We propose to calibrate the 36Cl method of exposure age dating up to 600 Ka. The 36Cl and 40Ar/39Ar methods will then be applied to Central Andes volcanic rocks to provide a chronological framework for late Pleistocene to Holocene volcanism in the Central Andes. The Central Andes has been selected for this pilot study because it is probably the finest example of continental volcanism in the world, and its high elevation and hyper-arid environment result in superb preservation (extremely low erosion rates) of volcanic features. In addition, since a high incident flux of cosmic rays is attained at high altitudes, cosmogenic isotope production rates will also be high. 36Cl depth profiles, and, if possible, 36Cl/10Be ratios will be determined to ensure that the erosion rate is well below that which would affect exposure ages. The proposed study will help to quantify several important scientific questions about central Andes volcanism: (1) the rate of growth and evolution of volcanic constructs, (2) the eruption frequency of lava flows and magma production rates, and (3) the correlation of 36Cl exposure ages and erosion rates with Landsat imaging data. The study is important as volcanism and tectonism are intimately related and any conclusions about the processes studied will likely be applicable globally.
