Geoscience Reference
In-Depth Information
convective-overturn time. Either interpretation is
circumstantial.
of renewed interest. The possibility that the shal-
low mantle is lithologically variable, containing
materials with higher latent basaltic melt frac-
tions than lherzolite, means that the mantle
can be more-or-less isothermal on a local and
regional scale, yet at given depth closer to the
solidi of some of the lithologies than others. Fer-
tile patches can also account for melting anoma-
lies along the global ridge system. Thus,
if the
upper mantle is sufficiently heteroge-
nous, plumes and high absolute temper-
atures are not required
as an explanation
for melting anomalies. The viability of the
ther-
mal
plume hypothesis boils down to the viability
of the assumption that the upper mantle is
chem-
ically
homogenous [
mantleplumes
].
Composition of OIB sources -
eclogite?
Subducted or delaminated basalt converts to
eclogite at depths greater than about 50 km.
Eclogites are not uniform; they includes extru-
sives, dikes, sills and diverse cumulates and
maybesuitable
protoliths
for composition-
ally distinct and diverse ocean-island basalts. The
possible roles of garnet pyroxenite and eclog-
ite in the mantle sources of flood basalts and
ocean
islands
have
recently
become
a
matter
