C. Meriaux et al., THE THERMAL SIGNATURE OF SUBDUCTED LITHOSPHERIC SLABS AT THE CORE-MANTLE BOUNDARY, Earth and planetary science letters, 160(3-4), 1998, pp. 551-562
We study the thermal structure around a cold deformable lithospheric s
lab as it sinks to the core-mantle boundary and migrates along it. We
present analytical results for the steady thermal structure establishe
d by a steady but spatially varying motion. The analysis gives a time-
like criterion for the thermal signature of a cold slab to persist by
the time that the slab moves along the core-mantle boundary. The model
is used to assess the feasibility of a purely thermal origin for some
of the observed seismic reflectors near the core-mantle boundary. Cal
culations of the time-like criterion show that the dynamical condition
s in our model, namely the velocity and the thickness of the descendin
g slab, are hard to reconcile with observations of subduction and seis
mic features. Seismic reflections and refractions from anomalously fas
t regions above the core-mantle boundary could be explained as thermal
slabs if the thickness of the slab at subduction was larger than 200
km or somewhat less if the slab did not split at the core-mantle bound
ary. A simple thermal model also predicts from mineral physics a certa
in correlation between S- and P-wave velocity anomalies, which is not
observed. However, a purely thermal origin cannot be ruled out if the
slab is buckling. This process could be in agreement with the observat
ions: the amplitude of the seismic anomalies, the vertical extent of h
igh-gradient zones and the P versus S comparisons. Chemical heterogene
ities and phase transformations remain alternative or complementary ex
planations. (C) 1998 Elsevier Science B.V. All rights reserved.