0000000000918931
AUTHOR
Bruce A. Kjarsgaard
Torngat ultramafic lamprophyres and their relation to the North Atlantic Alkaline Province
Geological mapping and diamond exploration in northern Quebec and Labrador has revealed an undeformed ultramafic dyke swarm in the northern Torngat Mountains. The dyke rocks are dominated by an olivine-phlogopite mineralogy and contain varying amounts of primary carbonate. Their mineralogy, mineral compositional trends and the presence of typomorphic minerals (e.g. kimzeyitic garnet), indicate that these dykes comprise an ultramafic lamprophyre suite grading into carbonatite. Recognized rock varieties are aillikite, mela-aillikite and subordinate carbonatite. Carbonatite and aillikite have in common high carbonate content and a lack of clinopyroxene. In contrast, mela-aillikites are richer …
Between carbonatite and lamproite - Diamondiferous Torngat ultramafic lamprophyres formed by carbonate-fluxed melting of cratonic MARID-type metasomes
Abstract New U–Pb perovskite ages reveal that diamondiferous ultramafic lamprophyre magmas erupted through the Archean crust of northern Labrador and Quebec (eastern Canada) between ca. 610 and 565 Ma, a period of strong rifting activity throughout contiguous Laurentia and Baltica. The observed Torngat carbonate-rich aillikite/carbonatite and carbonate-poor mela-aillikite dyke varieties show a large spread in Sr–Nd–Hf–Pb isotope ratios with pronounced correlations between isotope systems. An isotopically depleted component is identified solely within aillikites (87Sr/86Sri = 0.70323–0.70377; eNdi = +1.2–+1.8; eHfi = +1.4–+3.5; 206Pb/204Pbi = 18.2–18.5), whereas some aillikites and all mela-…
Integrating Ultramafic Lamprophyres into the IUGS Classification of Igneous Rocks: Rationale and Implications
RECEIVED JULY 16, 2004; ACCEPTED MARCH 16, 2005ADVANCE ACCESS PUBLICATION APRIL 29, 2005We introduce a modification to the current IUGS classificationsystem for igneous rocks to include ultramafic lamprophyres, whicharecurrentlyentirelyomitted.Thisisdonebyincludinganewstepinthe sequential system, after the assignment of pyroclastic rocks andcarbonatites, that considers ultramafic inequigranular textured rockswith olivine and phlogopite macrocrysts and/or phenocrysts. At thisstepultramaficlamprophyresareconsideredtogetherwithkimberlites,orangeites (former Group 2 kimberlites) and olivine lamproites.This proposal allows the correct identification and classificationof ultramafic lamprophyres w…
Craton reactivation on the Labrador Sea margins: 40Ar/39Ar age and Sr–Nd–Hf–Pb isotope constraints from alkaline and carbonatite intrusives
Abstract The once-contiguous North Atlantic craton (NAC) is crosscut by the Labrador Sea that opened during the Early Cenozoic after extensive Mesozoic continental rifting and removal of cratonic mantle. This large-scale structural change within the cratonic lithosphere was followed at about 150 Ma by the cessation of ultrapotassic and potassic-to-carbonatitic magma production, which had prevailed throughout much of the NAC history. At Aillik Bay, a sequence of olivine lamproites (1374.2 ± 4.2 Ma, 2σ), aillikites/carbonatites (590–555 Ma), and nephelinites (141.6 ± 1.0 Ma, 2σ) erupted through the southern NAC edge on the present-day Labrador Sea margin. Links between these alkaline magma ty…