On the direction of remanent magnetization of the quartz porphyry dikes in SE Finland

Abstract

Attempts are made to determine the direction of remanent magnetization of the rapakivi varieties belonging to the Wiborg (Viipuri) rapakivi massif and its satellites in the precambrian Baltic Shield. Hard and stable remanence was found only in the quartz porphyry dikes which are closely associated with the rapakivi granites and have a radiometric U-Pb age about 1630 Ma. The magnetization found evidently represents the direction of the geomagnetic field prevailing during the late phase of the evolution of the rapakivi magma. The calculated paleomagnetic pole site (30° N, 175° E with »normal» polarity) agrees well with those previously reported for rocks of about the same age in the Baltic Shield.

Keywords

• paleomagnetism
• polar wander curve
• rapakivi
• Precambrian (1630 Ma)