Petrochemistry, mineralogy, and Nd isotopic analyses of Tithonian alkaline lamprophyric intrusions, north-central Newfoundland, Canada

The Newfoundland Atlantic margin in Eastern Canada formed through protracted lithospheric extension, subsequent rifting, and ultimately, breakup. Mesozoic–Cenozoic magmatism on and offshore Newfoundland coincided with, and potentially resulted from, the concurrent rifting and breakup. In north-central Newfoundland, the alkali monzogabbroic Budgell Harbour and Dildo Pond stocks, an accompanying lamprophyre dyke swarm, and a peridotite sill collectively form the Notre Dame Bay Magmatic Province and are products of a punctuated alkaline magmatic pulse on the Newfoundland margin at ca. 148 Ma (Jurassic, Tithonian) with contemporaneous rifting and the formation of offshore petroliferous basins. The stocks comprise coarsely modally layered phlogopite–ilmenite–magnetite–kaersutite olivine gabbro or essexite. The radially disposed lamprophyre dykes are aphyric to ilmenite–magnetite–diopside ± olivine ± kaersutite ± phlogopite porphyritic camptonites containing common feldspathic- and/or carbonate-dominant ocelli. Silica-undersaturated (kirschsteinite), oxidized (esseneite, calderite), and incompatible-element-bearing minerals (barite, kainosite) form paragenetically late, small grains in the groundmass mantling other phases. Mineral chemistry, lithogeochemistry, and Nd isotopic data indicate the rocks are similar to ocean island basalt and alkaline lamprophyres and were generated via low degrees of partial melting of a Neoproterozoic, weakly garnetiferous lithospheric mantle source. The intrusions occur along the intersections of broadly northeast-trending, inherited, Appalachian-cycle lithospheric scale faults with a prominent east–west step in the northeast Newfoundland Mohorovičić discontinuity along the northeast Newfoundland coast. The convergence of inherited structures with the topographic variation of the lithosphere–asthenosphere boundary likely focussed decompression melting of the lithospheric mantle driven through distal, edge-driven upwelling associated with continued extension in the northwest Atlantic.