Abstract
Temperature is one of the key parameters controlling lithospheric
and mantle dynamics and rheology. Using recent experimental data
on elastic parameters and anelasticity, we obtain models of temperature
at 50 to 200 km depth beneath Europe from the global P wave velocity
model of Bijwaard et al. 1998 and the regional S wave velocity
model of Marquering and Snieder 1996. Forward modeling of seismic
velocity allows us to assess the sensitivity of velocity to various
parameters. In the depth range of interest, variations in temperature
(when below the solidus) yield the largest effects. For a 100C increase
in temperature, a decrease of 0.5-2\% in VP and 0.7-4.5\% in VS is
predicted, where the strongest decrease is due to the large effect
of anelasticity at high temperature. The effect of composition is
expected to give velocity anomalies <1\% for the shallow mantle and
would therefore be difficult to resolve. At depths >80 km the relative
amplitudes of the European VP and VS anomalies are consistent with
a thermal origin. At shallower depths, variations in crustal thickness
and possibly the presence of partial melt appear to have an additional
effect, mainly on S wave velocity. In regions where both P and S
anomalies are well-resolved, VP- and VS-derived thermal models agree
well with each other and with temperatures determined from surface
heat flow observations. Furthermore, the thermal models are consistent
with known tectonics. The inferred temperatures vary significantly,
from around 400C below an average mantle adiabat at 100 km depth
under the Russian Platform and a 300C increase from east to west
across the Tornquist-Teisseyre zone to temperatures around the mantle
adiabat in the depth range 50-200 km under areas with present surface
volcanism. In spite of the uncertainties in the calculation of temperatures
due to uncertainties in the experimental elastic parameters and anelasticity
and uncertainties associated with tomographic imaging, we find that
the tomographic models of the shallow mantle under Europe can yield
useful estimates of the thermal structure.
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