APPALACHIAN BASEMENT AND ITS INTRUSION BY CRETACEOUS DYKES, OFFSHORE SOUTHEAST NOVA-SCOTIA, CANADA

Aeromagnetic data collected between eastern Nova Scotia and southern N ewfoundland provide new information about the offshore extension of th e Avalon and Meguma terranes. A zone of short-wavelength anomalies tha t delineates Scatarie Ridge extends westward to the Late Proterozoic F ourchu Group in southeastern Cape Breton Island and eastward towards t he Burin Peninsula of Newfoundland, suggesting that both regions belon g to the same tectono-stratigraphic province of the Avalon composite t errane. A different zone of short-wavelength, discontinuously lineated anomalies at the northern edge of the Canso Ridge correlates with amp hibolite-facies metamorphic rocks of the Meguma terrane on the Canso P eninsula, interpreted as an exhumed deeper metamorphic level of the Me guma terrane at its boundary with the Avalon terrane. The S-shaped pat tern of long linear magnetic trends, characteristic of lower grade Meg uma rocks on the southern flank of the Canso Ridge, indicates plastic deformation of the Meguma terrane during the Acadian orogeny when empl aced against the rigid Cape Breton Island block indentor. Analogous pa tterns occur off western Nova Scotia, suggesting little strike-slip mo tion occurred between the Meguma and Avalon terranes since the Acadian orogeny. Late Proterozoic rocks on Scatarie Ridge are intruded by Cre taceous diabase dykes. The diabase is alkaline with a within-plate geo chemical signature, similar in composition to basalt flows in the Orph eus half-graben. A depleted-mantle model age T(DM) (Nd) of 731 Ma, eps ilon(Nd) = +6.5, suggests that the magma was sourced from a lithospher ic mantle reservoir involved in Late Proterozoic magmatic activity. Ae romagnetic data interpretation confirms the distribution of Cretaceous basalt flows and sills within Mesozoic sedimentary strata of the Orph eus half-graben previously outlined by seismic methods but was unable to differentiate between Proterozoic and Mesozoic intrusive rocks wher e the Proterozoic rocks lay near to the ocean floor.