A new geological map of the Holum granite and its gneissic envelope is presented. The pluton has sharp intrusive contacts with the surrounding migmatitic gneisses, contrasting with earlier interpretations of the granite as being of metamorphic origin and grading into augen gneiss. The granite gives a Rb/Sr age of intrusion of 1001 ± 34 m. y. and the augen gneiss an apparent age of 1 002 m.y. Low and similar initial ratios for the Holum granite (0.7045 ± 0.0003) and the surrounding augen gneiss (0.7040) suggest that they have a genetic relationship.
New light on the precambrian Holum granite, South Norway