CRUSTAL STRUCTURE OF THE MIDDLE URALS BASED ON REPROCESSING OF RUSSIAN SEISMIC-REFLECTION DATA

Reprocessed Russian seismic reflection data, combined with existing Ru ssian geological maps and seismic interpretations, provide the basis f or a revised tectonic interpretation of the upper crust in the Middle Urals. The Main Uralian Fault (MUF)-the principal suture of the Urals separating the East European Craton to the west from accreted terranes to the east-is found to penetrate to depths of at least 18 km, and pe rhaps much deeper, with a uniform eastward dip of 35 degrees (after mi gration). As the MUF appears to truncate reflections in both the forel and and hinterland of the Urals, it is arguably one of the youngest st ructural features of the orogen. Basement rocks of the East European P latform underthrust the suture and comprise the deep crust a minimum o f 30 km east of the surface expression of the MUF. The Tagil volcanic are complex, greater than 1000 km in length along strike, comprises at least the upper 10 km of the crust east of the MUF. This terrane shal lows eastwards, where it appears to be truncated by the west-dipping S erov-Mauk fault based on correlation with surface geology. The hinterl and of the Urals, east of the MUF, is characterized by a previously un recognized zone of discontinuous mid-crustal reflectivity at depths of 14-16 km that is discordant with upper crustal reflections. This mid- crustal zone of reflectivity is interpreted to represent either a majo r subhorizontal structural detachment or a zone of magmatic intrusion.