Provenance of the Newfoundland Appalachian foreland basins

Abstract

The tectonic history of the Appalachian orogen is recorded in the adjacent foreland. Offshore seismic data suggest that an initial, Middle Ordovician foreland basin was filled by sources in Newfoundland, whereas the Late Ordovician foreland basin was loaded and filled by sources to the SW, in the Québec segment of the orogen, where NW-vergent Taconian arc-continent collision may have continued later than in Newfoundland. We test this hypothesis using U/Pb ages of detrital zircon within foreland basin successions in western Newfoundland. Previously published results from the oldest foreland succession, the Middle Ordovician Goose Tickle Group, demonstrate ages similar to units preserved with the Humber Arm Allochthon, emplaced during Middle Ordovician Taconic orogenesis, including a predominant Paleoproterozoic peak at 1.85 Ga. In this study we investigated U/Pb geochronology of detrital zircon from younger foreland successions from Upper Ordovician to Devonian. The largest proportion of analyses within all foreland successions fall between 0.95 and 1.3 Ga, with largest peaks occurring between 1.0 and 1.1 Ga, typical of zircon derived from the Grenville Orogen. Earlier Mesoproterozoic and Paleoproterozoic ages range from 1.3 to 2.0. The abundance of Mesoproterozoic grains and conspicuous lack of 1.85 Ga Paleoproterozoic zircon in the overlying Upper Ordovician Long Point Group and latest Silurian to Early Devonian Clam Bank Formation indicates that these sediments were not derived from units within the Humber Arm Allochthon. Probability density plots of continental margin units in the Québec/New England segment of the orogen demonstrate a similar strong Mesoproterozoic and weak Paleoproterozoic signature, suggesting derivation of the Long Point Group from the Québec segment of the orogen. Within the mid-Paleozoic Clam Bank - Red Island Road succession, typical Gondwanan ages are absent and 1.0 Ga grains derived from the Grenville Orogen are abundant. This is consistent with underthrusting of the Gondwanan microcontinents Ganderia and Avalonia during Salinic and Acadian orogenesis. Only Mesoproterozoic zircon grains were found in the Early Devonian Red Island Road Formation, consistent with derivation from Mesoproterozoic Grenville massifs in western Newfoundland or Cape Breton Island which were exhumed during Devonian Acadian inversion.