Relation of Radiometric Age of Granitic Rocks near Calais, Maine, to the Time of Acadian Orogeny
Mineral and whole-rock ages by both K-Ar and Rb-Sr methods confirm an age of about 400 m.y. for the Red Beach and associated granites near Calais, Maine. Initial Sr 87 /Sr 86 is 0.712. Field relations in the area show that the Red Beach is post-early Lower Devonian and pre-Upper Devonian. Paleontologic-radiometric correlations elsewhere in the northern region suggest a period of intrusive activity in early-middle Lower Devonian. Evidence is accumulating that this igneous episode is fairly widespread in the northern Appalachians and is identifiable well beyond experimental error from the later and more pervasive episode at 360 m.y. associated with the main phase of Acadian orogeny.