Early Ordovician ages of zircons from felsic rocks and a conglomerate clast, Frosta peninsula, Central Norwegian Caledonides

Abstract

Zircons extracted from a felsic sheet in the bimodal, magmatic, Fånes complex of the Støren Nappe on Frosta peninsula yielded a U-Pb age of 488 \u00B1 5 Ma, interpreted as the age of crystallisation. A large clast of geochemically similar felsite in an overlying polymict conglomerate provided a U-Pb zircon age of 482 \u00B1 3 Ma. The presented crystallisation ages are thus mutually indistinguishable and indicate that the conglomerate was sourced, at least in part, from the Fånes complex. The age results constrain the accumulation of the Fånes complex to a Late Cambrian (Furongian) to earliest Ordovician (Tremadocian) time span, similar to the ages of other felsic extrusive or intrusive rocks in fragmented ophiolites or suprajacent, primitive, island-arc trondhjemites in the Trondheim Region.