Radiometric dating of Young MORB using the ⁴⁰Ar-³⁹Ar incremental heating method Public Deposited

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  • Determination of reliable crystallization ages by K-Ar methods for young (<1 Ma), fresh basalts from the seafloor has been frustrated by several effects. The small amounts of radiogenic ⁴⁰Ar developed over these timescales in such low-K rocks are difficult to resolve from predominantly atmospheric ⁴⁰Ar. An additional concern is that mantle-derived ⁴⁰Ar may not be totally outgassed when magmas quench at seafloor hydrostatic pressures. We have developed a successful strategy for partially separating atmospheric from radiogenic ⁴⁰Ar in ⁴⁰Ar-³⁹ Ar incremental heating experiments on mid-ocean ridge basalts, from the East Pacific Rise near the Clipperton Fracture Zone. Pre-heating samples to 400°C removes surficial atmospheric ⁴⁰Ar, while subsequent heating at 600°-1000°C produces favorable proportions of radiogenic ⁴⁰Ar. Experiments using "zero-age" glassy and holocrystalline samples show that mantle-derived ⁴⁰Ar is retained only in the outermost few cm of rapidly cooled pillow basalts.
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  • Duncan, R. A., and Hogan, L. G. (1994) Radiometric dating of young MORB using the ⁴⁰Ar-³⁹Ar incremental heating method. Geophys. Res. Lett., 21(18).
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