Crustal evolution of the Middle Urals based on seismic reflection and refraction data

Abstract

Integration of seismic refraction and deep reflection data from the Middle Urals of central Russia provides important new constraints on the structure of the Uralian crust. Re-analysis of the GRANIT refraction profile and comparison with coincident reflection data from the ESRU profile shows a high-velocity (7.6–7.8 km/s) root zone from c. 45 to 55 km with low reflectivity beneath the Urals. We interpret this interval as crustal material, consistent with previous Russian interpretations of this velocity anomaly. Above this crustal root, one of the principle features imaged on the ESRU profile is a thick zone (3–4 s TWT) of relatively strong reflectivity which may characterize the lower crust of the East European platform, but is considerably shallower to the east at 8–12 s TWT (25–37 km) than in the west at 10–14 s TWT (31–43 km). Reprocessing of 20 s records from the R-17 Profile in the West Siberian basin, ∼315 km northeast of the ESRU profile, reveals a similar pronounced lower-crustal reflectivity between 11–14 s TWT (34–43 km), in the hinterland of the Middle Urals. This lower-crustal reflection fabric may represent a feature developed during collisional orogenesis, or a younger property imparted through post-orogenic extension. Future deep reflection profiling will be critical to address the continuity, and accordingly, the tectonic significance of this lower-crustal reflectivity in the Urals.