The alkaline complex of the Breivikbotn area, Sørøy, Northern Norway.

Abstract

The alkaline rocks of the Breivikbotn area have been emplaced into highly folded and metamorphosed igneous and sedimentary rocks during the period of the Caledonian orogeny. They form an integral part of the complicated sequence of plutonic events that occurred during the orogeny, and were broadly syn-tectonic in relation to the second major period of deformation (F2). They have in fact been strongly folded and sheared by late expression of this movement phase. The alkaline rocks at Breivikbotn fall into two distinctive groups in terms of their field-relationships, mineralogical and chemical compositions. These are referred to as rocks of the Nepheline Syenite and Carbonatite Associations respectively. The first of these comprise nephelin syenite gneisses and pegmatites, alkali-syenite gneisses (without nepheline) and alkali feldspar-biotite-magnetites. The majority of the pegmatites and some of the sheets of nepheline syenite are intrusive types and appear to have resulted from the intrusion of a highly fluid pegmatite magma. Other rocks of this association such as the alkali-syenite gneisses, most of the nepheline syenite gneisses and some of the pegmatites, however, are products of metasomatism effected by fluids and emanations from the pegmatite magma.