PALAEOMAGNETISM AND GEOCHRONOLOGY OF MAFIC DYKES IN SOUTH SIBERIA, RUSSIA: THE FIRST PRECISELY DATED EARLY PERMIAN PALAEOMAGNETIC POLE FROM THE SIBERIAN CRATON

Abstract

New palaeomagnetic and geochronological data from mafic dykes emplaced into the basement of the Siberian Craton on the southwestern coast of the Baikal Lake are present. The concordant zircon U-Pb SHRIMP age of these dykes is 275 ± 4 Ma. Palaeomagnetic study of the dykes isolated a stable primary remanence with steep upward direction supported by a positive baked contact test. The palaeomagnetic pole (50.5°N, 121.4°E, A95 =16.7°) is the first precisely dated Siberian pole between ~360 and 260 Ma. It falls near the interpolated Siberian APWP and suggests that Siberia had not joined Eurasia by 275 Ma. The studied dykes are the first reported evidence of Permian magmatic activity in the cratonic part of southern Siberia. They are probably related to the prominent 300-260 Ma magmatic event recognized in Trans-Baikalia. The comparison of our new result with recently published palaeomagnetic data from Trans- Baikalia suggests that differential movements between the Siberian Craton and blocks of Trans-Baikalia around 275 Ma are unlikely. This confirms tectonic models considering Trans-Baikalia as an Andean-type active margin of the Siberian continent in Permian times. © 2006 The Authors Journal compilation © 2006 RAS.