<
p id="
p-1">The Southwest Indian Ridge, between 61° and 68°E, is one of the dee
pest, slowest, and coldest sections of the global mid-ocean ridge system, and the com
position of the basaltic crust suggests an extremely low degree of melting (
Meyzen et al., 2003). In contrast to normal ex
pectations, the subaxial mantle contains
peridotites highly de
pleted in clino
pyroxene (<2%), the lowest-melting mineral
phase, but anomalously enriched in ortho
pyroxene (modal olivine/ortho
pyroxene ≈ 2). Furthermore, ortho
pyroxene grains host mineral inclusions enriched in OH, Na, K, P, S, and light rare earth elements never
previously re
ported in residual mineral assemblages of abyssal
peridotites; these inclusions are
primarily Na-, Cr-rich dio
pside variably associated with a
patite, am
phibole, mica, albite, and sulfides. Sur
prisingly, these metasomatic minerals do not occur within the other mineral
phases (olivine, s
pinel) or as interstitial
phases or veinlets. We conclude that the metasomatic mineral inclusions re
present traces of a fertile mantle com
ponent that locally esca
ped extraction during decom
pression beneath the ridge. Our observations (1) im
ply interactions of the suboceanic asthenos
phere with incom
patible element–rich melts, and (2)
provide evidence for refractory mantle blobs in the suboceanic mantle that have com
positional similarities to continental lithos
phere.
p>