A synthesis of the geophysical characteristics of terranes in eastern canada

Abstract

Geological identification of terranes in the Canadian Appalachians has led, in general, to the proposing of terranes which have recognizably distinct geophysical signatures indicative of fundamental differences in crustal structure between the terranes. The rapidly expanding geophysical data base has enabled an integrated approach to geophysical terrane analysis. The geophysical data enable the Humber, with its diagnostic gravity low and variable magnetic anomalies, to be recognized throughout the Canadian Appalachians. Deep seismic data suggest that it is found beneath the western part of the Dunnage Terrane. The latter is typified by dominantly positive gravity anomalies in Newfoundland. These, together with the magnetic data, enable the zone to be subdivided into the Notre Dame and Exploits subzones. The seismic character clearly identifies the presence of the Dunnage northeast of Newfoundland and suggests that it may terminate south of Newfoundland. The Gander Terrane has typically negative gravity and magnetic anomalies which may be confidently traced from northeast of Newfoundland south through Cape Breton. A belt of similar anomalies occurs in New Brunswick. The deep seismic evidence suggests that the Gander may represent the outcrop of a deep crustal block underlying the eastern part of the Dunnage Terrane. The Avalon Terrane is identified throughout the Canadian Appalachians by a diagnostic set of arcuate, alternating gravity and magnetic anomalies. The boundary between the Avalon and Gander is clearly recognized on deep seismic sections as a near-vertical feature cutting through the crust northeast of Newfoundland. The Meguma/Avalon boundary is clearly delineated by a gravity and magnetic gradient throughout the system. There is limited and ambiguous deep seismic data regarding the nature of it and the Meguma Terrane in general. A subtle set of NW-trending lineations perpendicular to the dominant regional trend has recently been identified. Geological evidence that suggests these are post-Carboniferous in age and may be related to the development of a tensional regime associated with the Mesozoic rifting of the Atlantic.