Is there a 1.85Ga magmatic event in northern Norrbotten? - U-Pb SIMS zircon dating of the Pingisvaara metagranodiorite and the Jyryjoki granite, northern Sweden

Previously published discordant U-Pb zircon TIMS data of two granitoids from northern Sweden are here reassessed based on new U-Pb data acquired using the SIMS method. Zircon from the Pingisvaara metagranodiorite consists of older domains representing igneous crystallisation at 1881 +/- 5Ma and younger metamorphic domains dated at 1827 +/- 4Ma. The previous TIMS-age of 1856 +/- 8Ma for this sample is rejected. The previous, poorly constrained age determination of the Jyryjoki granite at 1853 +/- 21Ma, obtained by TIMS-analyses is herein improved using SIMS-technique. The new age at 1853 +/- 4Ma is interpreted to date igneous crystallisation of the granite. While 1.86-1.85Ga intrusive rocks are rare in northernmost Sweden there is growing evidence for metamorphic and hydrothermal activity in that time interval. The metamorphism at 1.83-1.82Ga recorded in zircon from the Pingisvaara metagranodiorite is consistent with a previously suggested protracted metamorphic event between 1.83 and 1.77Ga.