Stop 4 – Relationship between migmatites and felsic feeder dykes
Outcrops of migmatite and granite at the base of the Kameruka pluton (as shown in the lower Wog Wog River section) demonstrated that the migmatites generally pre-dated injection of granitic magma; only some granitic sheets hybridised with the diatexites, indicating synchronous intrusion. This section investigates the relations of migmatites to the inferred feeder dykes of the Kameruka suite. Here, we focus on a well exposed felsic dyke that occurs below the base of the Kameruka pluton.
The syn-to late-migmatite timing of the felsic dykes can be inferred from contacts, which range from sharp to diffuse. Where the dyke shows sharp margins, it truncates the migmatitic fabric at low angles, suggesting fracture propagation through a rigid medium. However, within several metres the dyke margin becomes diffuse, suggesting that partially melted diatexite and granitic liquid interacted after propagation of that dyke. These diffuse margins consist of complexly folded veins emanating into the diatexite, and appear to contribute much of the leucocratic material of those diatexites. They become less defined away from the dyke margin and are commonly parallel or subparallel to the migmatitic fabric. Locally, larger apophyses of dyke material emanated into the leucosome, forming convoluted veins with contacts that are gradational to the leucosomes. In places, the leucosomes and microgranite cannot be distinguished, indicating that mixing of the two phases has occurred.
These microgranite dykes are weakly folded, with axial planes parallel to the main shallow-dipping flow foliation in the diatexite (which is regional S3). This relation indicates intrusion of the dykes late in D3 and coeval with the migmatisation event, consistent with the local cross-cutting contacts with the migmatites.