COSMOGENIC NEON AND HELIUM AT REUNION - MEASUREMENT OF EROSION RATE

We report analyses of both helium and neon for olivine separates from a drill core at an attitude of 2330 m in oceanite at Piton de la Fournaise volcano. We show for the first time that cosmogenic Ne-21, like cosmogenic He-3, decreases exponentially with core depth. We obtain an attenuation length of 165 +/- 6 g cm 2 (1sigma) for cosmogenic Ne-21, identical to the value found previously for cosmogenic He-3 alone [1]. For each depth in the core, the measured amount of cosmogenic Ne-21 is about 13% lower than predicted based on the high precision K-Ar age of 65,200 +/- 2000 yrs (1sigma) [2], and this result is attributed to erosion. Assuming a constant erosion rate, we derive a value of 3.5 +/- 1.7 mm/yr (1sigma) from the Ne-21 data, the same order of magnitude as the value obtained from cosmogenic He-3 at Haleakala [ 1,3]. This work highlights the important potential of both cosmogenic helium and neon for measuring in-situ exposure ages and erosion rates.