Structure and petrology of the Bergen-Jotun kindred rocks from the Gjendebu region, Jotunheimen, Central Southern Norway.

Abstract

The Gjendebu region is located within the Jotun Nappe, highest tectonic unit of the southern Norwegian Caledonides. The structure of the area is dominated by the NE-rending Tyin-Gjende Fault, a major zone of repeated movement. To the northwest of this fault occurs a series of granoblastic ultrabasic, basic and intermediate gneisses (the Storådalen Complex) which show polyphase deformation and an intermediate-pressure granulite facies grade of metamorphism. To the southeast occurs an igneous-textured gabbro (Mjølkedøla Purple Gabbro) which grades eastward into the partially recrystallised Svartdalen Gneiss. Differences in major element composition between these units are minimal and they are belived to be comagmatic. Their geochemistry is broadly of calc-alkaline type, though all the rocks are anomalously potash-rich. The Storådalen Complex contains a complete differentiation in the origin of these rocks.