Genesis of intermediate igneous rocks at the end of the Sveconorwegian (Grenvillian) orogeny (S Norway) and their contribution to intracrustal differentiation

Abundant ferroan, metaluminous granitoids (970-950 Ma) emplaced at the end of the Sveconorwegian collisional orogeny (1130-900 Ma) are dominated by intermediate to silicic compositions with rare mafic facies. Both 73% fractional crystallization of an amphibole-bearing gabbroic cumulate substracted from the parent mafic composition and 30% non-modal batch melting of an amphibolitic source equivalent in composition to the mafic facies produce a monzodioritic liquid with appropriate trace element composition. A better fit is obtained for the partial melting process. Both processes could have occurred simultaneously to produce mafic cumulates and restites. As there is no evidence for large volumes of dense mafic rocks in the Sveconorwegian upper crust, these dense mafic rocks were probably produced in the lower crust. Formation of these granitoids, thus, contributed to the vertical stratification of the Proterozoic continental crust and also to the transfer of water from the lower crust to the surface.