HR: 14:25h
AN: U23B-04 INVITED     [Abstracts]
TI: The rapidly advancing field of applications of nuclides produced in terrestrial solids in earth and planetary sciences
AU: * Lal, D
EM: dlal@ucsd.edu
AF: Scripps Institution of Oceanography, Geosciences Research Division, La Jolla, CA 92093 United States
AB: The field of cosmogenic in situ nuclides in terrestrial solids is about 2 decades old, beginning with the realization that the commonly occurring mineral quartz allowed convenient study of in situ produced nuclides, 10Be and 26Al (Lal and Arnold, 1985; Nishiizumi et al., 1985)), which in turn provide estimates of cosmic ray irradiation history of quartz. Since then the field has continually developed, providing time scales in several disciplines of paleoclimatology, geomorphology, tectonics, meteorology, and volcanology. Realizing the importance of determining accurate time scales in earth sciences, several scientists joined in to implement a project: Cosmic-Ray-Originated Nuclide Systematics on Earth Project (CRONUS), for improving rates of production of cosmogenic nuclides in targets exposed to cosmic radiation under different conditions. These efforts will undoubtedly immensely increase the potentials of the cosmogenic in situ method. In modeling of the cosmogenic nuclide data, one generally faces a dilemma in most cases, namely that one does not have sufficient amount of useful geological data about the samples under study. For instance, one of the principal obstacles constraining exposure histories is the information on its erosion and exfoliation history during exposure. A new approach is feasible to tackle the above mentioned shortcoming utilizing the unique feature of the cosmogenic interaction, namely that the cosmic ray flux at a given point within an object depends on the angular distribution of path lengths of cosmic ray particles arriving at the point from different directions. Interestingly, this distribution continuously changes as the surface of the object evolves with erosion and/or exfoliation. Herein lies the potential of determining both the exposure history and the evolutionary history of the solid object under investigation from multiple determinations of nuclide concentration at different points within a target. We present as examples, exposure histories of boulders, soils and beach terraces, where one can take advantage of the fact that the magnitude of cosmic ray interactions in a solid is very sensitive to the geometry of irradiation, which allows constraining its evolutionary history.
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
DE: 4918 Cosmogenic isotopes (1150)
SC: Union [U]
MN: Fall Meeting 2005