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

• Published in: Geological Magazine
• Main Authors: RICE, A. H. N., NTAFLOS, T., GAYER, R. A., BECKINSALE, R. D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2004
• Subjects: Finnmark; Magerøya; Varangerhalvøy*; Varangerhalvøya
• Online Access: http://dx.doi.org/10.1017/s001675680300788x; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S001675680300788X

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.