New U/Pb zircon age constraints on the timing of deformation in north-central Newfoundland and implications for early Paleozoic Appalachian orogenesis

Abstract

U/Pb zircon ages of five felsic intrusions in eastern Notre Dame Bay bracket the absolute ages of a number of key units and events in the Newfoundland Appalachians. The age of 507 +3/-2 Ma obtained for the Twillingate pluton confirms an age obtained by earlier workers. It strengthens evidence of widespread Cambrian arc volcanism in Newfoundland and places a lower limit on the initiation of deformation in central Newfoundland. The Loon Bay suite, which includes the Loon Bay batholith and a swarm of quartz- and feldsparphyric tonalite dikes, has an age of 408 ± 2 Ma. This age places a Late Silurian upper limit on the timing of thrust fauting and three generations of folding in the New World Island area of Notre Dame Bay. This age also constrains the timing of sinistral ductile movement on the Reach fault and of initiation of high-angle brittle faulting in the region. An age of 422 ± 2 Ma for a composite mafic and felsic dike on the Port Albert Peninsula places an upper limit on the age of the Botwood Group in that area. This age also supports the correlation between the Botwood Group and mixed felsic and mafic igneous rocks of the Springdale Group in western Notre Dame Bay. Placed in context with the timing of other units and events in the Newfoundland Appalachians, our ages show that the formation and deformation of tectonic terranes making up the orogen did not take place in an orderly sequential fashion. Instead, at any one time, more than one tectonic element was being generated, subducted, or deformed. Although the locus of strain varied within the orogen, deformation occurred continuously from the Late Cambrian Epoch until the end of the Paleozoic Era.