A Tentative Model for the Origin of A-Type Granitoids

A-type granites are typically formed in stable intra-plate, back-arc or postcollisional settings and characterized by highly ferroan potassic major element compositions, strong enrichment incompatible trace elements. Unlike I-, S- M-type granites, where the letters denote dominant source material (igneous, sedimentary mantle derived), there is no consensus on processes giving rise to magmas. In this contribution, a conceptual model for origin of granitoids, using Bornholm granitoid complex southern Fennoscandia as an example, presented. model, underplated mantle-derived basaltic magma may develop into intermediate siliceous magma, which ferroan, enriched elements, through combination fractional crystallization leading cumulate formation, partial melting crustal assimilation, process akin zone refining metallurgy. The key factor relatively tectonic environment (postcollisional, anorogenic, extensional), little replenishment more primitive system, allowing it attain evolved, extreme compositions. granitoids then be viewed evolved counterpart subduction-related I-type granitoids.