Chronology and geochemistry of late Svecofennian processes in northern Sweden

Abstract

Abstract Radiometric and geochemical data have been used to characterize the concluding stages of the Svecofennian orogeny in northern Sweden. U-Pb zirzon ages of 1879±7 and 1858±9 Ma have been obtained from two unfoliated granitoids of the North Svecofennian Subprovince. The ages are distinctly different from each other and indicate late- to postorogenic Svecofennian magmatic activity 1860 Ma ago. The older rock type forms a diorite-quartz monzonite-adamellite trend, while samples of the younger type are adamellitic. Trace element data are not in accordance with a model where the younger type is formed by continuous magmatic differentiation from rocks of the older type. We propose a new 1910–1860 Ma delimitation for the emplacement of all igneous Svecofennian rocks in northern Sweden and conclude that the widespread potassic 1800–1770 Ma granites of that area should not be considered part of the Svecofennian orogeny, but of some later and separate event.