KINEMATICS OF THE MARTAIGA BLOCK OF THE KUZNETSK ALATAU PALEOISLAND ARC IN THE LATE VENDIAN-EARLY ORDOVICIAN ON THE BASIS OF PALEOMAGNETIC DATA

Abstract

The Vendian-Early Cambrian, Middle Cambrian, and Early Ordovician volcanosedimentary deposits of the Martaiga Block of the Kuznetsk Alatau paleoisland arc (55.5° N, 88° E) have been investigated paleomagnetically. Their paleomagnetic poles have been determined, permitting us to plot the apparent polar wandering path (APWP) of this block from late Vendian through Early Ordovician. On the basis of this APWP and comparative positions of paleomagnetic poles of the Martaiga Block and Siberian Platform, we succeeded in proving the kinematics of horizontal displacements of the Martaiga segment of the Kuznetsk Alatau paleoarc relative to the Siberian continent. This movement is characterized by southward drift from the equatorial latitudes of the Northern Hemisphere (about 10° N) to the tropical latitudes of the Southern Hemisphere (about 15° S); the velocity of the latitudinal component of movement reached its maximum in the Middle Cambrian (about 6 cm/year) and gradually attenuated by the Early Ordovician (about 2 cm/year); drift of the block was complicated by the clockwise rotation for more than 50°; the amplitude of rotation was about 1°/Ma and also attenuated from Cambrian to Ordovician. A considerable discrepancy between the Martaiga paleomagnetic poles and corresponding poles of the paleo-Siberian continent in the period from Vendian to Late Cambrian indicates that these tectonic units were separated in space. The collision of the Kuznetsk Alatau paleoarc with continent occurred in the Early Ordovician; their paleomagnetic poles did not differ at that time. It has been established that the formation of the modern structural plan of the Kuznetsk Alatau was due to large-scale displacement of structures along the periphery of the Siberian continent. The Martaiga Block and other tectonic units of the Kuznetsk Alatau paleoisland arc collided with the paleo-Siberian continent on the background of submeridional movements toward each other, with simultaneous clockwise rotation of the paleoarc.