Publication Date:
2019-07-17
Description:
Cratons with their thick lithospheric roots can influence the thermal structure, and thus the convective
flow, in the surrounding mantle. As mantle temperatures are hard to measure directly, depth variations in
the mantle transition zone (MTZ) discontinuities are often employed as a proxy. Here, we use a large new
data set of P-receiver functions to map the 410 km and 660 km discontinuities beneath the western edge of
the East European Craton and adjacent Phanerozoic Europe across the most fundamental lithospheric
boundary in Europe, the Trans-European Suture Zone (TESZ). We observe significantly shorter travel times
for conversions from both MTZ discontinuities within the craton, caused by the high velocities of the
cratonic root. By contrast, the differential travel time across the MTZ is normal to only slightly raised. This
implies that any insulating effect of the cratonic keel does not reach the MTZ. In contrast to earlier
observations in Siberia, we do not find any trace of a discontinuity at 520 km depth, which indicates a
rather dry MTZ beneath the western edge of the craton. Within most of covered Phanerozoic Europe, the
MTZ differential travel time is remarkably uniform and in agreement with standard Earth models. No
widespread thermal effects of the various episodes of Caledonian and Variscan subduction that took place
during the amalgamation of the continent remain. Only more recent tectonic events, related to Alpine
subduction and Quarternary volcanism in the Eifel area, can be traced. While the East European craton
shows no distinct imprint into the MTZ, we discover the signature of the TESZ in the MTZ in the form of a
linear region of about 350 km width with a 1.5 s increase in differential travel time, which could either be
caused by high water content or decreased temperature. Taking into account results of recent S-wave
tomographies, raised water content in the MTZ cannot be the main cause for this observation. Accordingly,
we explain the increase, equivalent to a 15 km thicker MTZ, by a temperature decrease of about 80 K. We
discuss two alternative models for this temperature reduction, either a remnant of subduction or an
indication of downwelling due to small-scale, edge-driven convection caused by the contrast in lithospheric
thickness across the TESZ. Any subducted lithosphere found in the MTZ at this location is unlikely to be
related to Variscan subduction along the TESZ, though, as Eurasia has moved significantly northward since
the Variscan orogeny.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
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isiRev
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