NEW PALEOMAGNETIC PALEOLATITUDES FOR THE OMULEVKA TERRANE OF NORTHEAST RUSSIA: A COMPARISON WITH THE OMOLON TERRANE AND THE EASTERN SIBERIAN PLATFORM

Abstract

Paleomagnetic measurements were made on samples from Silurian, Devonian, Carboniferous and Permian aged rocks from the Omulevka terrane, northeast Russia. The Omulevka terrane is a fragment of continental margin that forms a major component of the Kolyma–Omolon superterrane, a superterrane that constitutes the core of northeast Russia. All samples were collected from sites along the Taskan river, and all showed a very strong secondary overprint and in some cases more than one. With detailed thermal demagnetization, a component of magnetization that decayed towards the origin when viewed as an orthogonal plot was commonly present and showed better clustering of magnetization directions in stratigraphic coordinates. All of the sites sampled were tilted, but none had enough variation in bedding attitude to perform fold tests. Comparing data between localities was used as a pseudo fold test and indicates that in all but one case the characteristic remanent magnetization found represents a magnetization acquired very early in the history of the rock. Interpretation of these data in terms of both virtual pole positions and paleolatitude changes with time shows that the Omulevka terrane and the adjacent Omolon terrane were together at low latitudes in Silurian and Devonian time and until late Devonian their latitude was consistent with them being closely related to the Siberian Craton. Between Devonian and Permian times, the paleolatitudes of the terranes decreased and, when compared with equivalent reference paleolatitudes for the nearby Siberian platform, show a clear latitudinal separation. From Permian to Jurassic time, the Omulevka and Omolon terranes move steadily northwards, reducing the relative latitudinal separation from Siberia. By late Jurassic to early Cretaceous time, the observed and equivalent Siberian paleolatitudes are identical, indicating the accretion of the Kolyma–Omolon superterrane to the eastern Siberian continent.