Geochemistry and palaeogeographical setting of greenstone units on Frosta peninsula, Nord-Trøndelag, Central Norwegian Caledonides

Abstract

Volcanic and high-level intrusive rocks of the Støren Nappe exposed on the west coast of Frosta peninsula occur in two, distinct, magmatic units; the bimodal Fånes complex and the metabasaltic Granheim greenstone. North of Småland, the former unit is stratigraphically overlain by a conglomerate (Helsingplassen conglomerate) comprising clasts of Fånes rocks. Felsite clasts in this conglomerate are indistinguishable petrographically and geochemically from felsites occurring in thick sheets in the Fånes complex. South of Småland, the pillowed Granheim greenstone is unconformably overlain by the Huva conglomerate, composed largely of clasts derived from the greenstone, and in turn overlain by limestones and calcareous phyllites (Risset limestone) of Katian (Late Caradocian) age. The Granheim-Huva-Risset succession can be followed westwards onto the island of Tautra.