PALAEOMAGNETISM AND MAGNETOSTRATIGRAPHY OF THE PERMIAN-TRIASSIC NORTHWEST CENTRAL SIBERIAN TRAP BASALTS

Abstract

A detailed palaeomagnetic and magnetostratigraphic study of the Permian–Triassic Siberian Trap Basalts (STB) in the Noril'sk and Abagalakh regions in northwest Central Siberia is presented. Thermal (TH) and alternating field (AF) demagnetisation techniques have been used and yielded characteristic magnetisation directions. The natural remanent magnetisation of both surface and subsurface samples is characterised by a single component in most cases. Occasionally, a viscous overprint can be identified which is easily removed by TH or AF demagnetisation.The resulting average mean direction after tectonic correction for the 95 flows sampled in outcrops is D=93.7°, I=74.7° with k=19 and α95=3.3°. The corresponding pole position is 56.2°N, 146.0°E.Unoriented samples from four boreholes cores in the same regions have also been studied. They confirm the reversed–normal succession found in outcrops. The fact that only one reversal of the Earth's magnetic field has been recorded in the traps can be taken as evidence for a rather short time span for the major eruptive episode in this region. However, there is evidence elsewhere that the whole volcanic activity associated with the emplacement of the STB was much longer and lasted several million years.