Petrology of the Hyllingen gabbro complex, Sør-Trøndelag, Norway

The Hyllingen gabbro complex is a layered intrusive sheet lying in the eastern central Trondheim region. It is the southern part of the greater Fongen massif and is compcsed of a variety of rocks, ranging from ultrabasic to alcalic and acidic differentiates. The petrography and mineralogy of the various rock types are dealt with. The structure of the complex and its layered nature is described. Ten chemical and modal analyses of the rocks are presented from a traverse across the gabbro. The differentiation products show a combined 'normal' layered and a calc-alkaline trend caused by an initial high PH20 in the original magma and/or a high TiO2 content.