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Volcanic successions of Middle Devonian to Early Carboniferous age outcrop in northern mainland Nova Scotia and western Cape Breton Island. Current models of complex collision and suturing between North America and Africa during the Carboniferous suggest these lavas were erupted during a stage of compression and strike-slip ("transpression") at the plate-junctions.

Volcanics of the Fisset Brook Formation were sampled in three areas of western Cape Breton. Thirty-one rock units were analysed for their major and trace element contents. They include twenty-six basalts and andesites and five rhyolites. Electron microprobe analyses were obtained for a number of feldspars, clinopyroxenes and chlorites.

Two chemically distinct populations of mafic lavas were identified. The differences are due (1) to the magmatic affinity of the basalts; (2) to the mobility of K, Rb, Ti, Nb and Y in some of the lavas.

The petrogenetic model proposed involves cyclic eruptions tapping a progressively deeper source of magma within the crust. Contemporaneous basaltic and rhyolitic lavas were derived from a common source. The nature of the basement rocks, the changing depositional patterns in the stratigraphic sequence and the geochemical signature in the lavas are explained in terms of graben formation of the onset of rifting.

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Pages: 235
Supervisor: Becky Jamieson