Search

In the Eurasian part of the World Stress Map almost the whole region east of the Tornquist-Teisseyre line is terra incognita. The closure of this information gap is of fundamental importance to the understanding of the geodynamics of the Eurasian continent. A detailed analysis of stress-induced wellbore breakouts has been performed over a 4.1-km-long depth interval in the Vorotilov drillhole (VGS). The borehole is located in the central part of the Russian platform, right in the center of the Vorotilov meteorite impact crater 60 km to the NNE of the city of Nizni Novgorod. An ultrasonic borehole televiewer (BHTV) was used to obtain high-resolution acoustical images from the borehole wall. With an interactive system for analyzing BHTV data the azimuth and shape of borehole breakouts occurring in the depth range of 1.3–4.8 km were analyzed. A statistical analysis of the resulting orientation profile of the breakout azimuths yields an overall direction of the maximum horizontal principal stress S H of N 137°E ± 15°. Variations of breakout orientation with depth ranging from a few degrees up to more than 90° are seen on various depth scales. The observed stress direction of N 137°E agrees very well with the average S H orientation of N 145°E in Central Europe. If this measurement is taken as representative for the Russian platform, the stress field in Russia is only slightly rotated in comparison to Central Europe. This can possibly be interpreted as indicative for the stress field to be governed by broad scale tectonic forces, such as a strong contribution from the forces exerted by the collision zone in the Alpine-Himalayan belt and by the Mid-Atlantic ridge.

We review the structure and evolution of a number of Riphean-Phanerozoic rifts and extensional basins within the territory of the former Soviet Union (FSU). Horst-and-graben formation in strong crustal and subcrustal lithosphere layers can explain the multi-trough character of rift systems observed in the Russian platform, the Vilyuy rift, the West Siberian rift system, the Pechora-Kolva rift system and the Laptev Sea rift. Many features in the evolution of these rifted basins are incompatible with predictions of classical stretching models. Basin subsidence often occurs in the absence of any noticeable stretching and over time scales much longer than predicted by models of thermal subsidence. Other observations include a time gap between rifting and the onset of post-rift basin subsidence of tens to hundreds Ma and a correlation in timing of subsidence phases of rifted basins and platforms with opening and closure events of adjacent ocean basins. These observations point to an important role for mechanisms such as ecologite formation within or beneath the lithosphere as well as intraplate compression and stress-induced lithospheric deflection.