Cosmogenic neon and helium at Réunion: measurement of erosion rate

Abstract

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