PERMIAN PALAEOMAGNETISM OF EAST KAZAKHSTAN AND THE AMALGAMATION OF EURASIA

Abstract

Most of Kazakhstan belongs to the Ural-Mongol belt, the tectonic evolution of which is poorly understood as demonstrated by disparate tectonic models suggested thus far. We undertook a palaeomagnetic study of Upper Permian basalts and andesites from two localities in east Kazakhstan in order to evaluate the final stages of the evolution of this belt and Eurasian amalgamation. Thermal demagnetization revealed a single pre-tilting characteristic component of ubiquitously reversed polarity from all samples. The mean declination of this remanence from one locality agrees rather well with the Permian European palaeomeridian, whereas that from the other is clockwise rotated by 28°+/- 8°. The overall mean inclination of -49°+/- 4° differs by 9.7°+/- 4.2° from the reference inclination calculated, for our localities, from the Eurasian mean pole for the 245-260 Ma interval and is in agreement with 260-275 Ma data. We account for the observed pattern by either a slightly erroneous rock age (lithologies are somewhat older than indicated by geological data) or non-dipole (octopole) components of the geomagnetic field. Because significant relative motion of the study area with respect to Eurasia is not demonstrated, we conclude that welding of Kazakhstan, Europe and Siberia was essentially completed by Mid-Permian time.