Sequential injections of mafic magma into a crystallizing magma chamber—a case study from the Luleå area, northern Sweden

Abstract

During the emplacement and crystallization of a magmatic pluton, the physical properties of the melt will change with cooling. If magma of a more mafic composition is sequentially injected into more felsic magma before and during crystallization, the result will depend on when the mafic component was introduced. The interplay between changing viscosity, crystal content and temperature of the coeval magmas is critical for the finally developed structures. Patterns observed at a locality c. 4 km SW of the town of Luleå in northern Sweden have been interpreted in this context. At this locality, a coarse-grained gabbroid is cut by several dykes of both mafic and, in a later stage, felsic compositions. The dykes contain round to angular fragments of host material and the contacts between the dykes and the host vary from sharp to diffuse. Mafic microgranular enclaves in the gabbroid host are also common structures, which evidences the contrasting rheological behaviour of the different magmas.

Keywords:

• Magmatic pluton
• physical properties
• MME
• gabbroid host
• rheological behaviour
• Luleå
• magmatic evolution
• Bälinge magmatic breccia
• Archaean