NEON ISOTOPES IN SUBMARINE BASALTS

Abstract

Very large neon isotopic anomalies have been accurately measured in mid-ocean ridge basalt glassy samples from diverse locations worldwide. Values for20Ne/22Ne range up to ∼ 13 and21Ne/22Ne values range up to ∼ 0.07 (present atmospheric values are20Ne/22Ne= 9.8 and21Ne/22Ne= 0.029). The data are highly correlated in the20Ne/22Ne—21Ne/22Ne diagram, independent of sample location. Loihi seamount data show an atmospheric neon isotopic composition, which is consistent with previous He—Ar—Xe data and their interpretation as representative of a deep undegassed mantle source. Recent mixing within the mantle best explains the neon isotopic features, as well as the He—Ne—Ar—Xe relationships. We propose that the MORB21Ne/22Ne anomalies are due to nuclear reactions within the mantle. The origin of the20Ne/22Ne anomalies however cannot be explained in a straightforward way and we discuss several scenarios.