Petrology of differential gabbro sheets in the Altenes tectonic window, North Norway.

Abstract

The petrography of two differentiated gabbro sheets in the low-grademetamorphic Karelian supracrustal sequence of the Altenes Tectonic Window isdescribed. The intrusion have generally undergone extensive deuteric alter-ation. Detailed petrographic studies established the primary parageneses andvariation in the gabbro sheets and formed the basis for an interpretation ofthe geochemical profiles. Both intrusion have a distinct mineralogical andchemical variation suggesting that gabbro sheets in the window probablycomprise both sills and slightly inclined intrusions. Magmatic rocks in theAltenes Window describe a definite tholeiitic trend. Zr-FeO\/MgO and Zr-Y plotsof the two studied intrusions suggest the existence of two magmatic suites.The Trollvatn sill is interpreted as syngenetic with the mafic extrusive rockswhile the Sagelv intrusion probably intruded at a low angle in an early stageof the Svecokarelian orogeny.