Radiometric dating of the Horrsjö granite, south central Sweden

Abstract

U-Pb analyses of zircons from the Horrsjö granite, south central Sweden, give an upper intercept with concordia of 1850⁺⁸ ₋₇ Ma (1 sigma). The Horrsjö granite accordingly belongs to the synkinematic Svecokarelian intrusions. The zircons have no visible cores. Their positions on discordia are reversed in relation to the normal case, the smallest crystals having less than half the uranium content of the largest. This may be due to uranium loss caused by superimposed events of ser- and postorogenic Svecokarelian magmatism in the area. However, a recalculation with the new U-Pb systematics of Wickman (Wickman, F. E., 1983: Uranium-lead isotope systematics: The case of crystals with discrete cores. Lithos 16) yields an age of 1946 Ma. The age of 1850 Ma is accordingly a minimum age.

Key Words:

• Radiometric age
• U-Pb
• zircon
• synkinematic Svecokarelian
• Horrsjö granite
• Värmland
• Sweden
• N5948
• N5948
• E1412
• E1412