Spinel-bearing peridotite and pyroxenite xenoliths dredged from the
Dragon Seamount (southern Tore-Madeira Rise, West Iberia and Morocco
margin) give an insight into the composition of the underlying
lithosphere. These xenoliths are devoid of evidence of strong host
lava-peridotite interaction and re-equilibration or late impregnation in
the plagioclase facies. The spinels and pyroxenes from the Dragon
peridotites have compositions distinct from those of both Iherzolites
and harzburgites from the Iberia margin and the Mid-Atlantic Ridge. They
display a highly depleted composition, in particular, high Cr-number, up
to 0.63 in the spinels, consistent with a melting degree between 12 and
19%. Because of the strong chemical similarities between the
Tore-Madeira Rise, Newfoundland peridotites, and peridotites from
supra-subduction zones, we propose that the Dragon peridotites formed in
a similar context. The pyroxenites display a cumulate texture and are
probably a high-temperature-high-pressure cumulate formed by fractional
crystallization from a melt. The Tore-Madeira Rise peridotites may
represent a former mantle wedge in an oceanic arc, later included into
the continental lithosphere and finally tectonically disseminated within
the lithosphere during the rifting of the Newfoundland-Iberia
continental lithosphere. As a consequence, rifting processes may produce
heterogeneities in the oceanic lithosphere and influence isotopic
compositions of ocean island basalt-type lavas during plume-lithosphere
interactions, as inferred for the southern Tore-Madeira Rise.