Oroclinal bending of the Middle and Late Paleozoic volcanic belts in Kazakhstan: Paleomagnetic evidence and geological implications

Paleomagnetic data on Middle- and Late-Paleozoic rocks from the central part of the Ural-Mongolian Belt in Kazakhstan are considered. The primary remanences in the Permian rocks and secondary magnetization components of the same age in pre-Permian rocks of central and northern Kazakhstan are not rotated relative to the East European Platform. In southern Kazakhstan adjoining the Tien Shan almost all data point to large, up to 90A degrees, counterclockwise rotation of blocks. These rotations, related to the regional wrench fault zone, must be subtracted from older paleomagnetic data to ensure their correct interpretation. The paleomagnetic declinations in Upper Carboniferous rocks coincide more or less over all of Kazakhstan, whereas the Silurian and Early Devonian declinations in the north and south of Kazakhstan differ approximately by 180A degrees. It can be suggested that the Devonian volcanic belt, having a horseshoe outline, was initially an almost rectilinear NW-trending feature. Its oroclinal bending took place in the Devonian and Early Carboniferous and completed by the Late Carboniferous. We compared the model of the Kazakh Orocline based on paleomagnetic data with the geological events in this territory. It turned out that a slow bending of an initially rectilinear subduction zone is consistent with lateral migration of active volcanism and folding inside a developing loop, whereas extension outside the loop was accompanied by subsidence and rifting. In general, the proposed model connects the main tectonic events in Kazakhstan with the movements established from paleomagnetic data.