James Gregory Davison

B. Sc. Honours Thesis

⁴⁰Ar/³⁹Ar, ⁴⁰K-⁴⁰Ar and Paleomagnetic Dating, Petrochemistry and Opaque Mineralogy of Dolerite Dykes in the Hopewell Area, Southwestern Pictou County, Nova Scotia.

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A detailed petrochemical, paleomagnetic, and geochronologic study has been made on dolerite dykes outcropping near upper Paleozoic Windsor and Canso strata. The dykes are located in two map sectors, Marshdale and Centredale, approximately three kilometers southwest and ten kilometers south, respectively, of Hopewell, southwestern Pictou County, Nova Scotia.

Petrochemical studies, carried out in conjunction with the two dating techniques, suggest tholeiitic diabases Large phenocrysts of pyroxene, both hypersthene and augite, and plagioclase feldspar, An50-70' dominate the mineralogy. Ilmenite is present as highly exsolved lamellae within magnetite as well as primary grains. Magnetite is found as both primary and secondary phases.

Conventional potassium-argon ages were determined on three plagioclase separates and one whole rock sample. ⁴⁰Ar/³⁹Ar apparent ages from 1 plagioclase separate were plotted as an age spectrum. The results indicate a minimum age of intrusion of 270-310 Ma (Upper Carboniferous to Lower Permian). Sericitization may influence the isotopic properties of the dykes.

After alternating field demagnetization, a "stable" remanence was established for seven of fourteen cores. The paleolatitude of 13^oN suggests Triassic magnetization. The pole position for the dykes of 20^oN 70^oE is discordant from the inferred polar wander path although correlation with Triassic data was indicated. The paleomagnetic results may be affected by a remagnetization episode. This suggests that the results place a minimum on the age of a primary magnetization.

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