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Extending 10Be applications to carbonate-rich and mafic environments

By
Régis Braucher
Régis Braucher
CEREGE: UMR 6635–CNRS, IRD, Université Paul Cézanne, Plateau de l'Arbois, BP 80, 13545 Aix-en-Provence, France
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Pierre-Henri Blard
Pierre-Henri Blard
CEREGE: UMR 6635–CNRS, IRD, Université Paul Cézanne, Plateau de l'Arbois, BP 80, 13545 Aix-en-Provence, France
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Lucilla Benedetti
Lucilla Benedetti
CEREGE: UMR 6635–CNRS, IRD, Université Paul Cézanne, Plateau de l'Arbois, BP 80, 13545 Aix-en-Provence, France
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Didier L. Bourlès
Didier L. Bourlès
CEREGE: UMR 6635–CNRS, IRD, Université Paul Cézanne, Plateau de l'Arbois, BP 80, 13545 Aix-en-Provence, France
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Published:
January 01, 2006

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.

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Contents

GSA Special Papers

In Situ-Produced Cosmogenic Nuclides and Quantification of Geological Processes

Ana María Alonso-Zarza
Ana María Alonso-Zarza
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Lawrence H. Tanner
Lawrence H. Tanner
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Geological Society of America
Volume
415
ISBN print:
9780813724157
Publication date:
January 01, 2006

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