Geophysical Laboratory, Carnegie Institution of Washington, Washington, D.C. 20008. Present address: Department of Geological Sciences, University of California, Santa Barbara, Santa Barbara, California 93106
Early Paleozoic ophiolite complexes crop out in three main northeast-trending belts in Newfoundland. Zircons separated from trondhjemite that occurs as a late-stage differentiate within ophiolite yielded nearly concordant ages; this indicated formation of the Bay of Islands belt about 508 m.y. ago (Late Cambrian time) and the Betts Cove belt about 463 m.y. ago (Middle Ordovician time). The difference in age supports the idea that each ophiolite belt is the product of a separate spreading episode in independent, narrow, newly rifted ocean basins, marginal basins, or rifts.