Commingling of Contrasted Magmas in the Plutonic Environment: Examples from the Nain Anorthositic Complex

Abstract

Within the Nain anorthositic complex Fe-rich dioritic magma has mixed with and commonly been chilled by granitic magma in several different structural settings. The dioritic magma was residual from associated anorthositic plutons and was essentially anhydrous; most of the was hydrous with a composition near the granite minimum and probably originated by partial melting of crustal rocks. The commingling of these granitic and dioritic magmas indicates that the massive granitic plutons were emplaced during the solidification of some of the anorthositic bodies. The lower temperature behavior and hydrous composition of the magmas argue against comagmatic relations between and the anorthosite-diorite association either by fractional crystallization or liquid immiscibility. The generation of large volumes of may reflect increased heating of the lower crust related to the emplacement of the anorthosites. Granite magmas appear to have risen through pockets of relatively dense ferr...