Neoproterozoic to lower Paleozoic basin and platform strata that formed during and after rifting along the western Laurentian margin are preserved in the northern Cordillera. Several pulses of magmatism occur within margin strata and are concentrated along the Dawson fault in central Yukon. Magmatism is dated as late Cambrian and Late Ordovician using: 1) U-Pb zircon geochronology of volcaniclastic rocks; and 2) fossil ages from strata interbedded with, and enclosing, volcanic rocks. Volcanic rocks from both pulses are predominantly alkaline and basic and erupted in subaqueous environments. The trace element geochemical compositions of the rocks suggest that they formed from partial melting of enriched lithosphere from the garnet stability field.