Granites and the Nature of the Variscan Crust

The orogenic crust of the European Variscan belt is granite-rich and only locally has a mafic lower layer. The core of the belt originated by massive melting of fertile quartzo–feldspathic sources (felsic meta-sedimentary or meta-igneous) derived from an Ediacaran–Ordovician accretionary system. An unusually felsic lower crust formed either by relamination of previously subducted continental crust or by melting of crustal rocks to produce a granitic upper crust and a laminated, restitic lower crust. This is in strong contrast to conventional models, developed mainly for magmatic arcs, that find or infer mafic lower crustal compositions. Thus, global estimates on the nature and evolution of the continental crust should consider the heterogeneity of the deep crust produced in various types of orogenies.