Age measurements on minerals from the Cutler batholith, Cutler, Ontario

Mineral ages have been measured by the K-A, Rb-Sr, U-Pb, and Th-Pb methods on samples of granite and pegmatite from the Cutler batholith, Ontario. The pegmatites crosscut the granite and thus are clearly younger than the granite. However, Rb-Sr ages of both pegmatitic muscovite and feldspar agree at about 1750 m.y. whereas Rb-Sr and K-A ages of the granitic biotites agree at about 1300 m.y. Most other ages are intermediate. These apparent discrepancies are interpreted as the result of a hypothetical event that took place 1300 m.y. ago, 400 m.y. after the original crystallization of the batholith. No clear petrographic evidence is found for such an event. These data show that consistent results by a single method on different minerals, or by several methods on a single mineral species, do not necessarily indicate the time of original crystallization of a granitic body. In spite of these complexities, these data show that the Cutler granite was formed prior to the time of the Grenville metamorphism and igneous intrusion, and should not be considered to be of very late Precambrian age.