Mafic dike swarms represent direct evidence of early tensional environments that may have eventually led to ocean formation. The first precise U-Pb zircon and baddeleyite age of 615 ±2 Ma for a Long Range southeastern Labrador, could mark the beginning of Iapetus Ocean formation. Baddeleyite (ZrO2) is more widespread than previously recognized. It is ideal for use with the U-Pb system because it has low initial common lead and sufficient uranium levels, and it does not lose significant radiogenic lead with time. Baddeleyite therefore provides a unique opportunity for dating dikes associated with rift-related events with un-precedented accuracy.