Gerencher's MS Page
MS Thesis title: Structural Relationships, Petrography, Chemistry, and Magnetic Properties of Some Dike Swarms in and around the Mutton Bay Pluton, Quebec.
Click to see illustrations of
dikes viewed from sea
dikes near coast
The results of the study were presented as a paper at the Third Annual Meeting of the Northeastern Section of the Geological Society of America in Washington, DC on Feb 16, 1968. The abstract for the paper, written with D. P. Gold, thesis advisor, appears below:
The Significance of Some Dike Swarms along the North Shore of the Golf of Saint
Lawrence in Eastern Quebec
Gerencher, J. J. and D. P. Gold
Dikes are well exposed along the coast near Mutton Bay and La
Tabatiere, about 80 miles southwest of Labrador, in an area underlain by a 15-mile
diameter syenite pluton. The pluton is dated at 650 m. y. (Davies, 1966) and
intrudes Grenville gneisses. Structural studies and field relations of the dikes and
fractures indicate that the dikes are preferentially oriented parallel to the coast, but
have no definitive relationship to the fractures.
The chronological sequence of dikes is (1) aplite dikes associated with late-stage consolidation of the syenite; (2) alkali gabbro dikes containing phenocrysts of titanaugite; (3) red microsyenite and black camptonite dikes, appearing to be the most common; (4) nepheline basalt and micromonzonite dikes; and (5) breccia veins consisting of feldspar and quartz fragments in a finely crushed matrix.
The position in the intrusive sequence of the carbonate dike containing fragments of micromonzonite and of a limbergite dike is not known.
Magnetic studies on 21 samples did not yield a consistent paleomagnetic vector.
The alkaline character of these dikes contrasts with that of the basaltic dikes near Mingan and on Anticosti Island which intrude Ordovician limestone and with post-Lower Cambrian flood basalts in southern Labrador and on Newfoundland. The recent suggestion (Kumarapeli and Saull, 1966) that the Saint Lawrence Valley represents a rift valley system of possible Mesozoic age is appealing, in that the dikes parallel the coast and exhibit alkaline affinities, as do the intrusives in the Monteregian Petrographic Province near Montreal.