He and Ne isotopic ratios from the Terceira Rift (Azores): Constraints on the boundary between Eurasia and Nubia mantle sources

Abstract

We present He and Ne isotopic data from subaerial and submarine samples collected along the Terceira Rift. Graciosa Island as well as the western end of S. Miguel Island and D. João de Castro Bank display 4He/3He ratios similar to those observed along the MAR segments located to the north of the Azores Triple Junction area. Conversely, samples from the south Hirondelle Basin display a 4He/3He ratio similar to that of the MAR segments located to the south of the Azores Plateau. The Terceira Rift is thus characterized by the mingling of two different mantle domains referred as ‘Eurasia’ and ‘Nubia’ type. He and Ne systematics shows that the influence of the relatively primitive source sampled by the Azores plume can be followed along the Terceira Rift from the Graciosa Island towards the south Hirondelle Basin. Moreover, samples from the south Hirondelle Basin, D. João de Castro Bank and Graciosa Island cannot be explained by the same hyperbolic mixing model that encloses Terceira data.