Crustal Structure of Collisional Orogens: The Ural Mountains, Russia

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9219915 Brown The Ural Mountains of central Russia form a 3,000-km linear orogenic belt of Paleozoic age and constitute a unique natural laboratory to address a number of basic issues concerning collisional orogenesis and the evolution of continental crust. Several features appear to distinguish the Urals from other Paleozoic orogenic belts such as the Appalachians, Caledonides, and Variscides. Primary among these are (1) the apparent presence (based on seismic velocities) of a preserved crustal root below the Urals, (2) the apparent lack of syn- or post-collisional collapse evidenced in the Urals based on existing data, (3) the relatively shallow crustal level and generally low metamorphic grade exposed in the Urals, and (4) the nature and distribution of crustal reflectivity in the Ural orogen. In particular, the apparent similarity in early orogenic evolution between the Urals and the Appalachians, and the subsequent divergence in post-orogenic paths, offer a special opportunity to evaluate the role of various orogenic processes in the development of lower crustal structure. For example, if the prominent lower crustal layering observed beneath the Appalachian interior relates to post-orogenic extension, will it be absent beneath the Urals? Do the Urals preserve an intermediate stage in orogenic development between the more mature collapsed orogens like the Appalachians and more recent compressional belts like the Alps and Himalayas? The Principal Investigators will initiate a collaborative research program with Russian scientists at the Bazhenov Geophysical Expedition in Scheelite (near Ekaterinburg, formerly Sverdlovsk), Russia, for a comprehensive study of the nature and origin of the crustal structure of the Urals based on their extensive existing geophysical database. This collaboration constitutes the initial phase of a larger, long-term program to compare and contrast the Urals with other Paleozoic orogens, eventually leading to the first deep seismic reflection profile across the Urals. This effort also represents the first collaboration between US scientists and EUROPROBE, a major new European initiative to coordinate lithospheric studies in Europe. The US component will focus on a comparison of Uralian and Appalachian structure, complementing EUROPROBE's investigation of the Urals versus Variscan evolution. In particular they will focus on reprocessing and synthesis of Russia reflection (mostly shallow), refraction and DSS (deep seismic sounding) data, with the aim of mapping the crustal structure and understanding the Phanerozoic history of the Urals and nearby regions. In doing this, they will be establishing with their Russian collaborators a common knowledge of the various existing datasets and their interpretations. It is important to note that the Bazhenov Expedition is the center for all geophysical data available on the Urals (including DSS and reflection data, gravity and magnetic data, heat flow, etc.) and the majority of these data, are of unrestricted access under the conditions of a joint statement with scientists from that institute. ***