Paleogeographic development of the east Laurentian margin: Constraints from U-Pb dating of detrital zircons in the Newfoundland Appalachians

An upper Neoproterozoic to Ordovician Laurentian margin sedimentary sequenc e in the Newfoundland Appalachians records a cycle of ocean opening and clo sing. U-Pb dating by ion microprobe of 341 detritalzircon grains from six s amples from this sequence yielded ages from 3592 +/- 5 Ma to 572 +/- 14 Ma. Three of the analyzed samples are from rift-related formations, two are fr om drift-related formations, and one is from a foreland-basin unit. The U-P b data allow grouping of the zircons into four major age components: (1) Ar chean grains with a maximum age frequency between 2850 and 2600 Ma, (2) Pal eoproterozoic grains ranging from 1950 to 1750 Ma, (3) Mesoproterozoic to e arly Neoproterozoic grains ranging in age between 1450 and 950 Ma, and (4) Neoproterozoic grains ranging between 760 and 570 Ma. The relative proporti ons of these four age components vary among samples. Mesoproterozoic detrit us is present in all samples, whereas Neoproterozoic detritus is restricted to two of the three rift-related samples. Two samples - one from a rift-re lated formation and one from a drift-related formation, but both lying at t he base of their stratigraphic column-lack Paleoproterozoic and Archean det rital zircons. Potential source regions for the detrital zircons occur within the Laurenti an hinterland: zircons of Archean age correspond to the age of rock units f ormed during major magmatic and tectonothermal pulses in the Superior crato n, zircons with Paleoproterozoic ages correspond to the ages of orogenic be lts marginal to the craton (e.g., Ungava, New Quebec, and Torngat), Mesopro terozoic zircons correspond to the ages of lithologies from the Grenville o rogen, and Neoproterozoic zircons are the age of rift-related igneous activ ity along the Laurentian margin that is now preserved within the Appalachia n orogen. The youngest grains in the rift-related sedimentary rocks yield a ges of 580-570 Ma and provide a maximum age for accumulation of the Newfoun dland sedimentary sequence.