The geological and tectonic evolution of the precambrian of northern Sweden — A case for basement reactivation?

Abstract

Abstract This study is the result of a regional mapping programme of the Precambrian to the extreme north of Sweden by the Geological Survey of Sweden in the years 1976–1981. It takes into account most of the geological, geochemical and geophysical data concerning the region. A brief description and revision of the stratigraphy is given, in the light of recent mapping results and radiometric age determinations. An attempt is made to trace the main petrogenetic trends of the volcanic and the plutonic rock series in order to determine which geotectonic model can best be inferred for the region. Following the Archaean consolidation phase, two major tectonic episodes have been recognized: (1) a tensional episode characterized by incipient rifting which resulted in the extrusion of basic magma and in the deposition of predominantly quartzitic sediments and (2) a complex episode of reactivation of older structures and formations, corresponding to the peak of the Svecokarelian orogeny and to later consolidation. This tectonic evolution is interpreted here as a phase of basement reactivation and shows much resemblance to ‘ensialic mobile belts’ described in other parts of the world. A characteristic feature of the aeromagnetic, gravimetric and Landsat maps is the profusion of circular and arcuate structures of variable magnitude and distinctiveness. The possibility that some of these are due to the process of sequential inheritance of early impact scars is discussed.