POTASSIUM-ARGON AGE DETERMINATIONS OF CENOZOIC VOLCANIC ROCKS FROM BRITISH COLUMBIA

Potassium-argon age determinations of 13 Cenozoic volcanic rocks from southern and central British Columbia indicate one to be 62 million years old (Paleocene), nine to be 45–53 million years old (Eocene), and three to be 10–13 million years old (early Pliocene or late Miocene). The concentration of Eocene dates suggests a distinct volcanic episode roughly contemporaneous with tectonic activity in the Rocky Mountains to the east. The lack of dates from 45 to 13 million years and the development of a mature erosion surface by the more recent date suggest a prolonged stage of tectonic quiescence in southern and central British Columbia in mid-Cenozoic time.