Magma sources for some mid-Proterozoic granitoids in SE Sweden: Geochemical and isotopic constraints

Abstract

Three granitoid suites from near Linköping, SE Sweden, belong to a major belt of mid-Proterozoic (post-Svecokarelian) magmatic rocks which displays Andinotype geological characteristics. The suites have sub-alkaline major element geochemistry and ‘within plate’ trace element (high Y, Nb) characteristics. Meta-aluminous chemistry and low Ga contents suggest dominantly igneous sources. Assuming an intrusion age of around 1.7 Ga, Sm-Nd isotope systematics indicate an average crustal residence period of about 0.2 Ga. One interpretation of these data is that these suites have developed in an Andinotype environment, not necessarily as subduction generated marginal suites but possibly in an ensialic rift environment on the continental side of a hypothetical calc-alkaline belt. An alternative interpretation is that the ‘within-plate’ trace element characteristics are inherited from a Proterozoic crustal precursor.