Author(s):
Madureira, Pedro 
; Moreira, Manuel ; Mata, João
Date: 2005
Persistent ID: http://hdl.handle.net/10174/2447
Origin: Repositório Científico da Universidade de Évora
Subject(s): Neon isotopic data; Azores hot spot
Description
The collection of helium isotopic data in the last twenty
years has shown different signatures for MORB and OIB
basalts and this has been used as the basis for the two-layer
mantle model. However, for some OIB that appear in the
vicinity of mid-ocean ridges, He isotopic ratios are similar to
those typical of MORB, leading some authors to argue against
the deep mantle plume hypothesis particularly in areas where
geophysical evidence is lacking (Anderson, 2000).
For Terceira island (Azores), located close to the Mid-
Atlantic Ridge, we analysed neon from olivine phenocrysts in
order to better constrain the nature of the Azorian plume.
Some of the analysed samples show higher 20Ne/22Ne and
21Ne/22Ne ratios than air suggesting the presence of a mantle
component in the olivine melt inclusions. Moreover, in a
three-Ne isotope diagram, the samples define a trend with a
higher slope than the MORB line (Sarda et al., 1988) arguing
for a lower mantle origin. One basaltic sample coming from
the 1998 submarine Serreta eruption is plotted along this line,
suggesting that the influence of a deep plume is still active. In
a plot of 21Ne/22Necorr vs. 4He/3He, Terceira data is plotted in
the same hyperbolic mixing line that encompasses Iceland,
Shona and Discovery data (Moreira et al., 1995, 2001; Sarda
et al., 2000). The data suggests the existence of plume-ridge
interaction for these hotspots resulting on mixing between
degassed MORB-type and deep plume-type magmas. In such
an environment the data shows that neon is a better tracer of
primordial material than helium.
