CENOZOIC STRIKE-SLIP TECTONICS IN ALTAI

Abstract

The geodynamic framework of the Altai mountainous province has been modeled on the basis of structural data. The Altai mountains formed by brittle deformation and plastic flow of crustal material at the southern and western boundaries of the Mongolian microplate in the field of regional compression caused by the India-Eurasia collision. Two principal flows were directed northwestward and eastward. Crustal shortening occurred in elongate strike-slip zones and was accompanied by subsidence of the Moho and growth of mountains. The latter occurred along reverse faults (or, less often, along thrusts) or was associated with large-magnitude motions on major strike-slip faults. Cenozoic vertical offset along individual faults has been 3 - 4 km, and the amount of horizontal displacement attains 40 km. In the northwestern segment of the province within the Russian Altai, the amount of horizontal displacement along strike-slip faults has been partially reduced as the major faults split into north-striking tension faults and west-striking reverse faults. The area of mountains increased at the account of marginal parts of stable surrounding blocks involved in the uplifting. As evidenced by the modern seismicity mostly concentrated along the main fault boundaries of Altai, the process that started in the Oligocene and became more active in the latest Neogene continues at present.