Primitive neon isotopes in Terceira Island (Azores archipelago)

We present the first neon data, as well as new helium data, on Terceira Island (Azores archipelago, Portugal). Clear Ne-20 and Ne-21 excesses compared to air are observed (Ne-20/Ne-22> 11.2) and moreover, the samples show a more primitive Ne-21/Ne-22 ratio than MORB, confirming that the Azores hotspot can be considered as sampling a "primitive", relatively undegassed, reservoir. Most He-4/He-3 isotopic ratios range between 80,000 and 63,500 (similar to 9 to 11.5 R/Ra), being similar to those previously reported by [1] [M. Moreira, R. Doucelance, B. Dupre, M. Kurz, C.J. Allegre, Helium and lead isotope geochemistry in the Azores archipelago, Earth Planet. Sci. Lett. 169 (1999) 189-205]. A more primitive He-4/He-3 ratio of similar to 50,000 (R/Ra similar to 15) was obtained in one sample, but we cannot completely exclude the possibility of a cosmogenic He-3 contribution for this sample. Our study illustrates that the neon systematics can be more capable than helium to constrain the ultimate origin of hotspots in geodynamic settings dominated by plume-ridge interaction. (C) 2005 Elsevier B.V. All rights reserved.