Metadolerite geochronology and dolerite geochemistry from East Finnmark, northern Scandinavian Caledonides

Abstract

Dolerite dykes in the East Finnmark Scandinavian Caledonides form three geochemical suites: Digermulhalvøya–Magerøya – WNW–ESE-trending, c. 337–332 Ma, possibly also c. 293 Ma, continental within-plate; East Varangerhalvøya – NE–SW and N–S, c. 376 Ma, continental plate-margin; Styret – NE–SW, also c. 376 Ma, chemically intermediate to the other two groups. New K–Ar data from metadolerites on Varangerhalvøya give a 7-point ‘lower envelope’ isochron of 577 ± 14 Ma (MSWD 1.04). This is concordant with a published upper intercept U–Pb zircon age (567⁺³⁰₋₂₃ Ma) from an East Varangerhalvøya dolerite, here re-interpreted to reflect Neoproterozoic basement fracturing contemporaneous with the emplacement of the metadolerites. Intrusion of the younger dolerites at c. 376 Ma reactivated this trend, and may be responsible for the published zircon lower intercept age of 392⁺²⁵₋₃₆ Ma. Clarification of the intrusion and structural chronology, integrated with extensive new geochemical data, enables a better understanding of the evolution of this part of the Scandinavian Caledonides.