THE VOLCANIC TO NON-VOLCANIC MARGIN TRANSITION OFF NOVA SCOTIA

The rifted continental margin along the Atlantic coast of eastern North America is classified as volcanic, with thick sequences of igneous material emplaced at the continent-ocean transition during Late Triassic to Early Jurassic rifting. A strong, linear magnetic anomaly is observed along the margin from the Blake Spur fracture zone to the Scotian margin. Off Nova Scotia, the East Coast magnetic anomaly (ECMA) changes character, becoming disjointed and lower in amplitude until it fades east of Sable Island into the regional background level. The loss of magnetic signature plus changes in other characteristics such as the disappearance of seismic seaward dipping reflectors (SDRs) have suggested that the Scotian margin is primarily non-volcanic, with the transition occurring northeast of Georges Bank. However, this interpretation has not been conclusively substantiated.

New wide-angle seismic reflection / refraction data were collected in 2001 across the ECMA off southwestern Nova Scotia. Preliminary interpretations of the data provide estimates of the thickness and lateral extent of the volcanic layers, and help to identify the continent-ocean transition along this part of the margin. This new information is being used to constrain simple 2D models of magnetic structure, to compare the Scotian margin volcanic volumes and magnetization parameters with those determined for the US margin. The results provide insight into the changing thermal and mechanical conditions that led to the gradual reduction in volcanism and eventual transition to a non-volcanic style of rifting along the Scotian margin.