GEOCHRONOLOGY, PETROLOGY AND LITHOGEOCHEMISTRY OF MESOZOIC ALKALINE LAMPROPHYRIC INTRUSIONS, NEWFOUNDLAND, CANADA: IMPLICATIONS OF MAGMATIC EVOLUTION FOR NORTH ATLANTIC OPENING

The magma-poor Newfoundland margin offshore Eastern Canada formed after a period of lithospheric stretching and rifting that was likely well underway by the Late Jurassic. Rifting was followed by breakup separating the Grand Banks and Iberia, and northern Newfoundland from Ireland in the Aptian-Albian. Mesozoic-Cenozoic magmatism is documented on- and offshore Newfoundland contemporaneous with, and possibly related to, rifting and breakup, including the Mesozoic Notre Dame Bay Magmatic Province. This relatively small magmatic province comprises multiple sets of lamprophyre dykes and at least two gabbro-pyroxenite intrusions, one of which is termed the Budgell Harbour Stock (BHS). Here, we use SEM (scanning electron microscopy) techniques including MLA (mineral liberation analysis) and EMPA (electron micro probe analysis), along with lithogeochemistry, optical mineralogy, and geochronology to study the evolution of these magmatic rocks. The lamprophyre dykes range from phaneritic to aphanitic and the dominant phenocryst phases are titaniferous augite and phlogopite, with less common olivine and hornblende. When noted, olivine is commonly strongly serpentinised. The lamprophyre dykes also contain widespread leucocratic globules (ocelli) within a more mafic matrix indicating evidence of separation of immiscible silicate liquids in the melt. The BHS is medium- to coarse-grained and contains the same phenocryst species but locally with a greater abundance of olivine and clinopyroxene. Borehole cuttings indicate that the BHS is itself cut by comparable lamprophyre dykes. Lithogeochemical and mineral chemical data indicate that the dykes are camptonitic lamprophyre and the BHS essexite; the latter representing non-layered cumulate residues of the former. A new CA-ID-TIMS U-Pb age for zircon in the BHS, and ⁴⁰Ar/³⁹Ar laser step-heating on phlogopite from both the BHS and lamprophyre intrusions confirm a substantial magmatic event on the Newfoundland margin at ca. 148 Ma (Jurassic, Tithonian). This is contemporaneous with significant rifting, and the formation of the offshore rift basins. Comparison of this new age with determinations from rift-related magmatic rocks on conjugate margins and adjacent regions reveals similar age occurrences across the proto-North Atlantic region at ca. 150-140 Ma.