Cenozoic strike-slip tectonics in Altai

The geodynamic framework of the Altai mountainous province has been modeled on the basis of structural data. The Altai mountains formed by brittle def ormation and plastic flow of crustal material at the southern and western b oundaries of the Mongolian microplate in the field of regional compression caused by the India-Eurasia collision. Two principal flows were directed no rthwestward and eastward. Crustal shortening occurred in elongate strike-sl ip zones and was accompanied by subsidence of the Moho and growth of mounta ins. The latter occurred along reverse faults (or, less often, along thrust s) or was associated with large-magnitude motions on major strike-slip faul ts. Cenozoic vertical offset along individual faults has been 3-4 km, and t he amount of horizontal displacement attains 40 km. In the northwestern seg ment of the province within the Russian Altai, the amount of horizontal dis placement along strike-slip faults has been partially reduced as the major faults split into north-striking tension faults and west-striking reverse f aults. The area of mountains increased at the account of marginal parts of stable surrounding blocks involved in the uplifting. As evidenced by the mo dern seismicity mostly concentrated along the main fault boundaries of Alta i, the process that started in the Oligocene and became more active in the latest Neogene continues at present.