Relict Dikes in the Coast Mountains near Vancouver, B.C.

Many of the dikes in this area exhibit conflicting age relations with the plutonic rocks which contain them. Some of the dikes show clear evidence of having been replaced by the same plutonic rocks they evidently cut. Conflicting evidence is also provided by the associated extrusives, which, although they rest on and contain boulders of, plutonic rock, are dioritized and locally intruded by this same rock. The writers suggest that these dikes are essentially contemporaneous with the formation and evolution of the plutonic rock and that therefore the plutonic rock, while it was evolving by metasomatism and recrystallization, was capable of sustaining fractures. It can be demonstrated that breaks in the plutonic rock, either faults or joints, were present after the intrusion of some of the dikes and that these breaks have since totally healed by recrystallization. For the study of plutonic rocks the dikes described afford a useful tool.