Craton reactivation on the Labrador Sea margins: 40Ar/39Ar age and Sr–Nd–Hf–Pb isotope constraints from alkaline and carbonatite intrusives

• Published in: Earth and Planetary Science Letters
• Main Authors: Tappe, Sebastian, Foley, Stephen F., Stracke, Andreas, Romer, Rolf L., Kjarsgaard, Bruce A., Heaman, Larry M., Joyce, Nancy
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2007
• Subjects: Labrador Sea; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/44683/; https://oceanrep.geomar.de/id/eprint/44683/1/Tappe.pdf; https://doi.org/10.1016/j.epsl.2007.01.036

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 types with diverse petrogeneses as a consequence of large-scale processes in the lithospheric mantle over a period of 1200 Myr are demonstrated utilizing their Sr–Nd–Hf–Pb isotope compositions. The Mesoproterozoic olivine lamproites are characterized by unradiogenic Nd (εNd(i) = − 8.4 to − 5.4), Hf (εHf(i) = − 11 to − 7.8), and Pb (206Pb/204Pb(i) = 14.2–14.8) but moderately radiogenic Sr isotope compositions (87Sr/86Sr(i) = 0.7047–0.7062) fingerprinting long-term enriched cratonic mantle, which must have reached to depths of more than 150 km at this time. In contrast, Neoproterozoic carbonate-rich aillikites and carbonatites have fairly radiogenic Nd (εNd(i) = 0.1–1.8), Hf (εHf(i) = − 0.9 to + 2.6), and Pb (206Pb/204Pb(i) = 17.5–18.8) but unradiogenic Sr isotope compositions (87Sr/86Sr(i) = 0.7033–0.7046) that point to the involvement of convective upper mantle material during melting. Simple binary mixing calculations coupled with the observation that carbonate-rich magmatism prevailed for over 30 Myr in the area imply a complex pattern of lithosphere–asthenosphere interaction at depths between ∼180 and 140 km. The Cretaceous nephelinites have slightly unradiogenic Nd (εNd(i) = − 4 to − 1.4), moderately radiogenic initial 87Sr/86Sr (0.7044–0.7062), but initial εHf (− 3.3 to + 1.4) similar to the aillikites and highly radiogenic Pb ...