STRUCTURE OF THE LITHOSPHERE ALONG THE CEL05 PROFILE IN BELARUS (WESTERN PART OF THE EAST EUROPEAN CRATON): CONSTRAINTS FROM GEOLOGICAL AND NON-SEISMIC GEOPHYSICAL DATA. E. Kozlovskaya, L. Taran, G. Karatayev, V. Astapenko, J. Yliniemi. Sodankyla Geophysical Observatory / Oulu Unit, University of Oulu, POB 3000, 90014, Oulu, Finland, E-mail: elena.kozlovskaya@oulu.fi. Belarusian Research Geological Exploration Institute Kuprevich 7, 220141 Minsk, Belarus E-mail: taran@geology.org.by. Institute for Nature Management, National Academy of Sciences of Belarus E-mail: german@nature.basnet.by.

The crust in the Fennoscandian part of the Belarusian-Baltic region is represented by a collisional assemblage of Palaeoproterozoic terranes of different age and varying grades of metamorphism. The 1.9-1.85 Ga old amphibolite- to granulite-facies Belarusian-Lithuanian terrane comprises the Bela-rusian-Podlasie granulite (BPG) and East Lithuanian (EL) belts representing different depth levels of the crust. The collision tectonics resulted in a high thickness (around 50 km) of the crust. The prevalence of linear and linear-striped NW- and NE-trending positive and negative magnetic anomalies is the typical feature of the area. The EW-trending ca. 1.5 Ga old Polotsk-Kurzeme fault zone (PKZ) clearly cuts the pre-existing tectonic pattern.

A new opportunity to study this important tectonic boundary was provided by the CEL05 wide-angle reflection and refraction profile that is a part of CELEBRATION 2000 (Central European Lithospheric Experiment Based on Refraction). The northern part of the profile (700-1420 km) stretches along the BPG and crosses the southern margin of the PKZ. The profile revealed a difference between crustal and upper mantle P-wave velocities beneath the BPG and northern part of the PKZ and an upper mantle reflector beneath the southern demarcation of the PKZ at a depth of 60-65 km. In this study the authors tried to find more evidence for the difference between the PKZ and BPG using results of the other seismic studies in the Belarusian-Baltic region, analysis of laboratory measurements of rock properties, 3-D density modeling and results of previous magnetotelluric (MT) studies. The 3-D gravity modeling of the area around the CEL05 revealed that the BPG and pKz crust have different density values. Previous MT studies revealed two conductivity anomalies at depths of 20 km and about 120 km within the PKZ. These anomalies are absent from the BPG. All this suggests that the PKZ may represent an ancient terrane boundary that could have been reactivated ca. 1.5 Ga ago and an important present-day intraplate tectonic boundary.