C. Mellqvist, Sequential injections of mafic magma into a crystallizing magma chamber - a case study from the Lulea area, northern Sweden, GFF, 121, 1999, pp. 43-48
During the emplacement and crystallization of a magmatic pluton, the physic
al properties of the melt will change with cooling. If magma of a more mafi
c composition is sequentially injected into more felsic magma before and du
ring crystallization, the result will depend on when the mafic component wa
s introduced. The interplay between changing viscosity, crystal content and
temperature of the coeval magmas is critical for the finally developed str
uctures. Patterns observed at a locality c. 4 km SW of the town of Lulea 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 la
ter stage, felsic compositions. The dykes contain round to angular fragment
s of host material and the contacts between the dykes and the host vary fro
m sharp to diffuse. Mafic microgranular enclaves in the gabbroid host are a
lso common structures, which evidences the contrasting rheological behaviou
r of the different magmas.