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Russian Geology and Geophysics

2005 year, number 5

THE AGE OF SHEAR DEFORMATIONS IN THE OL'KHON REGION, WESTERN CISBAIKALIA (from results of 40Ar/39Ar dating)

V.P. Sukhorukov, A.V. Travin, V.S. Fedorovsky*, and D.S. Yudin
United Institute of Geology, Geophysics and Mineralogy, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
* Geological Institute of the RAS, 7 Pyzhevsky per., Moscow, 119017, Russia
Keywords: 40Ar/39Ar dating, shear deformations, western Cisbaikalia
Pages: 567-571

Abstract

New data on the age of shear deformations in the Ol'khon region (western Cisbaikalia) are reported. The Ol'khon collisional system has an intricate folded structure with three successively formed parageneses: nappe, domal, and shear. Shear deformations appeared at the final stages of the formation of this region and determined its general structure. The age of the deformations has been first estimated by 40Ar/39Ar dating of minerals with indications of shearing genesis. It has been established that the shearing took place 445-434 Myr ago, i.e., much later than the peak of metamorphism of granulite facies (480-500 Myr ago). The data obtained also suggest the existence of a thermal event (no earlier than 415 Myr ago), which led to a partial re-equilibration of the isotopic system.