Аннотация:The carbon budget and dynamics of the Earth’s interior, including the
core, are currently very poorly understood. Diamond-bearing, mantlederived
rocks show a very well defined peak at δ13C≈−5 ± 3‰with
a very broad distribution to lower values (∼−40‰). The processes
that have produced the wide δ13C distributions to the observed low
δ13C values in the deep Earth have been extensively debated, but
few viable models have been proposed. Here, we present a model
for understanding carbon isotope distributions within the deep
Earth, involving Fe−C phases (Fe carbides and C dissolved in Fe−Ni
metal). Our theoretical calculations show that Fe and Si carbides can
be significantly depleted in 13C relative to other C-bearing materials
even at mantle temperatures. Thus, the redox freezing and melting
cycles of lithosphere via subduction upwelling in the deep Earth that
involve the Fe−C phases can readily produce diamond with the observed
low δ13C values. The sharp contrast in the δ13C distributions of
peridotitic and eclogitic diamonds may reflect differences in their
carbon cycles, controlled by the evolution of geodynamical processes
around 2.5–3 Ga. Our model also predicts that the core contains C
with low δ13C values and that an average δ13C value of the bulk
Earth could be much lower than ∼−5‰, consistent with those of
chondrites and other planetary body. The heterogeneous and depleted
δ13C values of the deep Earth have implications, not only
for its accretion−differentiation history but also for carbon isotope
biosignatures for early life on the Earth.