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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS017 Oral Presentation 2361
Heat flow variation with depth in Poland and Central Europe from deep
equilibrium temperature logs and litosphere thermal state
Dr. Jacek Majorowicz
IASPEI
Jan Safanda, Vladimir Cermak, Marta Wroblewska, Jan Szewczyk, Stanislaw
Wybraniec, Marek Grad, Aleksander Guterch
High precision, deep, temperature depth (T-z) logs were obtained in three deep wells in Poland some
three decades after the drilling ceased. These new logs give unique thermal equilibrium information for
the western margin of the Precambrian craton and the Variscan accreted terranes. A heat flow of 50-60
mW m-2 was determined in the lower 900 m of a 2900 m deep well at Torun (western part of the
Precambrian craton) using estimated thermal conductivities from net rock analyses and measured
thermal conductivities on core samples. We determined, using functional space inversion of the entire
temperature-depth profile, that postglacial warming at Torun was 10-15 C. A 1044 m T-z profile at
Czeszewo well (the Variscan platform) does not sample the region below the post-glacial warming
signal, but our analysis also showed an increase in heat flow with depth in the region. The estimated
heat flow is 65.1 mW/m**2. After correcting for the transient effects of post-glacial warming in the
Czeszewo well, we estimated steady-state heat flow at 2 km depth to be 84.7 mW m-2 to 86.6
mW/m**2,which agrees with heat flow estimates from below 2 km in other wells in the area. These
changes in heat flow with depth are consistent with a model of the glacial cycles (90 - 25 - 90 - 25 -
...ka) with temperatures (0 - 14 - 0 - 14C - ..) and temperature before the onset of the cycles equal to
the weighted average of one cycle [(90*0C + 25*14C)/115ka = 3.05 C]. In Udryn-Sidorowka wells (low
heat generation norite -anorthosite intrusion in NE Poland - Precambrian craton) combined T-z from 2
profiles gives significant increase of heat flow with depth. Deep heat flow is 40 mWm-2 at 2.3km. The
estimated paleosurface temperature is -10C (Safanda, Szewczyk, Majorowicz.,2004 GRL). It is
consistent with other studies in Central Europe in deep wells in Czech Republic, Slovenia and in the KTB
well in Germany (Safanda & Rajver, 2001 GPCH; Clauser et. al, 1997 JGR).These study confirm that
deep heat flow map of Central Europerequires correction and only deepwell heat flowdeterminationsare
usefull for lthermal lithosphere modeling. These corrected deep heat flow values were used through
Central Europe to studythermal litosphericstate. Large variations in the uppermost mantle velocity (from
less than 7.9 km/s to >8.5 km/s) through the area of Poland and Central Europe suggest a transition
between low velocity hot southern southwestern part and high velocity cold mostly northern and northeastern
part. This does not exactly agree with deep heat flow data in many areas of the Variscan inner
and outer zones. High heat flow zones (>80mW/m**2) occur in the areas of highest Pn velocities (>8.2
km/s) while low heat flow zones (40-60 mW/m**2) occur in areas having relatively low Pn velocities
(7.9-8.05 km/s). On the other hand, there is a good relationship between heat flow, crustal thickness,
and elevation that is consistent with a simple isostatic model of the major tectonic units in Central
Europe. This suggests to us that large compositional changes exist in the mantle below the Variscan
foreland in TESZ (Trans-European Suture) zone.
Keywords: paleo heat flow, thermal litosphere, permian basin