Extending 10Be applications to carbonate-rich and mafic environments
Published:January 01, 2006
Régis Braucher, Pierre-Henri Blard, Lucilla Benedetti, Didier L. Bourlès, 2006. "Extending 10Be applications to carbonate-rich and mafic environments", In Situ-Produced Cosmogenic Nuclides and Quantification of Geological Processes, Ana María Alonso-Zarza, Lawrence H. Tanner
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Quantitative geomorphologic studies using cosmogenic nuclides in carbonate-rich and mafic environments have up to now been restricted to the cosmogenic radio-nuclide 36Cl (T1/2 = 0.31 m.y.), and to the stable 3He and 21Ne cosmogenic nuclides, respectively. To extend the time span and erosion rate range quantifiable in carbonate-rich environments, and to provide the possibility to decipher complex exposure histories by differential radioactive decay over several Ma in mafic environments, the in situ production rate of 10Be (T1/2 = 1.5 m.y.), the nuclide with the longest half-life of the well-established terrestrial cosmogenic radionuclides, has been determined in calcite and clinopyroxenes.
The development of new chemical decontamination procedures efficiently removing meteoric 10Be from carbonates and altered clinopyroxenes allows determining 10Be production rates. A 10Be production rate in clinopyroxenes of 3.1 ± 0.8 atoms/g/yr at sea level and high latitude is proposed from measurements of 10Be and 3He concentrations in K-Ar-dated Quaternary basaltic flows of Etna volcano.
Through measurements of 10Be and 36Cl concentrations in the same calcite samples and of 10Be concentrations in depth profiles of flint from the same erosional surface, a value of 37.9 ± 6.0 atoms/g/yr has been determined for the 10Be production rate in calcite at sea level and high latitude. Approximately sixfold higher than production in the coexisting flint, this higher rate of production may be due to high production cross sections for C spallation by cosmic rays with energies below 50 MeV. These results also open the possibility of dating burial events in carbonate-rich environments by differential radioactive decay of 10Be and 36Cl.