The posttectonic St. Lawrence and François granites have long been regarded as the youngest Paleozoic plutonic suites of the Newfoundland Appalachians. Their U–Pb ages of 374 ± 2 and 378 ± 2 Ma, respectively, define a Middle to Late Devonian magmatic event. Mid-Carboniferous magmatic and (or) rifting events, suggested on the basis of earlier Rb–Sr dating of the St. Lawrence Granite, are not supported by these new data. Both granites intrude major ductile and brittle structures that were active during the early Paleozoic, and they provide a younger age limit for major tectonic activity in the Avalon Zone and on the south coast of Newfoundland. The granites may correlate with plutons of closely similar age reported from the Aspy and Mira terranes of Cape Breton Island, Nova Scotia.

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