Secondary and Primary Growths in the Zircons from Paragneisses and Migmatites of Arvika (Sweden) and Nelaug (Norway) Regions

Secondary growths which include overgrowths, outgrowths, and multiple growths are formed during metamorphism and partial melting. Primary growths include growth twins and parallel growths. Twinning may occur during the early crystallization of zircon in magmatic rocks. The process of synneusis may result in parallel growths or attachment of zircons that have initially undergone separate growth histories.

The occurrence of primary growths in paragneisses and migmatites is due to their derivation from magmatic sources and their survival during mechanical transportation and crushing of the samples at the time of separation.