Collaborative Research: Nuclear Studies of Continental Erosion Processes and Rates

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This is a continuation of an experimental program to further develop and apply a nuclear method for studies of earth- surface geologic processes, including studies of continental erosion. The technique is based on in situ production of nuclides in rocks by nuclear interaction of cosmic rays. Since the absorption mean free path of cosmic radiation is - 50 cm in rocks, and since in situ nuclides, 10Be (half-life, 1.5X106 yrs), 26Al (half-life, 0.7X106 yrs) and 14C (half-life, 5730 yrs) can easily be studied in most rocks, one can optimally characterize surficial changes in the bracket 2X10-5-6X10-3 cm.yr-1; higher and lower rates are accessible using shorter half-life nuclides (39Ar, half-life 269 yrs) and stable nuclides, 3He and 21Ne respectively. We have already demonstrated the potential of the method based on studies of in situ 10Be and 26Al in quartz extracted from some 50 rock samples. We have studied their production rates in quartz in natural settings, and also by irradiating quartz with high energy particles. And we have studied surface erosion rates and exposure histories of several rocks, and also determined the time of formation of the Canyon Diablo meteorite crater in Arizona. The measurements carried out have established the potential of the nuclear method proposed 2 years ago by us to NSF. We now propose to continue our measurements for another period of 2 years to fully develop and to exploit the potentials of the in situ method. Briefly: we will include studies of in situ 14C in quartz; we will obtain further data on isotope production rates; we will continue studies of surficial erosional rates of selected surfaces. In addition, we proposal a set of new applications of the nuclear method, e.g. studying faulting and history of global sands. The use of multiple in situ nuclides has the now realized potential to revolutionize the understanding of surficial processes by opening up the vast majority of earth's surface to the numerical age control.