DEEP-STRUCTURE OF THE CONTINENTAL LITHOSPHERE IN AN UNEXTENDED OROGEN- AN EXPLOSIVE-SOURCE SEISMIC-REFLECTION PROFILE IN THE URALS (URALS SEISMIC EXPERIMENT AND INTEGRATED STUDIES (URSEIS 1995))

Explosive-source near-vertical seismic reflection data from the Urals Seismic Experiment and Integrated Studies (URSEIS) profile displays an image of orogenic lithosphere to depths of 225 km. The reflective cru stal section is characterized by dipping, crustal-scale shear zones, a nd a pronounced crustal root that show no evidence of overprinting by extension and are preserved since late Paleozoic collision. Toward the east, the Uralian crustal root is composed of a partially subducted v olcanic are, while to the west it has affinity with the East European platform. The reflection character of the Moho varies across tectonic strike and implies that the Moho (1) acted as a structural detachment beneath the Trans-Uralian Zone, (2) forms a tectonic boundary between terranes beneath the East Uralian Zone, (3) consists of a transitional zone from eclogitized lower crust to peridotitic upper mantle in the crustal root, (4) is a 3-9 km thick reflective zone beneath the fold a nd thrust belt, and (5) is a boundary <200 m thick in the west. Mantle reflections at 80-100 km depth (22-24 s) may represent a continuation of the Main Uralian fault into the subcrustal lithosphere. Alternativ ely, these reflectors may signify Paleozoic or younger mantle shear zo nes or the top of a zone of partial melting in the upper mantle. Deepe r mantle reflections at 140-160 km (35-45 s) and 225 km (55 s) may ima ge mafic intrusions at the base of the lithosphere or along localized shear zones in the upper mantle.