Building the Eurasian Supercontinent: Paleomagnetic Study of Kazakhstan to Assess its Role in Uniting Baltica with Siberia

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Eurasia contains several older cratonic blocks that are united by intervening younger mountain belts; the latter account for about half of the Eurasian landmass. Whereas the motions during the last 500 million years of these large Eurasian blocks and the evolution of the Alpine-Himalayan-Indonesian belt are relatively well defined, the tectonic history of the Paleozoic mountain belts remains enigmatic. One of the largest and least understood is the Ural-Mongol belt, which unites the North-European, Siberian, North China, and Tarim blocks. In its central part in Kazakhstan, the Ural-Mongol belt attains great width and consists of a nest of some three or more horseshoe-shaped, strongly curved structures. The ages of the rocks in these structures range from about 520 to about 280 million years ago, and all represent ancient island-arcs, which undoubtedly were built above subduction zones where large ancient oceanic domains were recycled into the Earth's mantle. How these structures became assembled in the Ural-Mongol belt of Kazakhstan and how this assembly occurred within the large-scale late Paleozoic amalgamation of Eurasia can become better understood if the prior spatial distribution of its tectonic elements can be determined. Detailed paleomagnetic studies on rocks of varying ages within the structures are able to achieve this goal. Rocks from different parts of the highly arcuate structures in Kazakhstan are being collected in order to determine the latitudinal motions of the island-arc units prior to and during their assembly into the structures. These motions of Kazakhstan units can then be compared with the motions of the surrounding cratons of Northern Europe, Siberia and Tarim during the assembly of Eurasia. In addition the project will test the hypothesis that the strongly curved structure of Kazakhstan resulted from large-scale bending of an originally nearly straight series of island arcs. In the broadest geological sense, it is noteworthy that the late Paleozoic mountain belt of southern Europe and several late Precambrian belts (e.g., in Arabia and northeast Africa) show important similarities with Kazakhstan. A successful model for the Kazakhstan domain may serve as a useful analog for other pre-Mesozoic accretion processes during the amalgamation of supercontinents.