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Early Eocene Arctic volcanism from carbonate-metasomatized mantle

Day, James M. D.; Pearson, D. Graham; Kjarsgaard, Bruce A.; Barker, Abigail K.; Nowell, Geoff M.; Joyce, Nancy; Lowry, David; Sarkar, Chiranjeeb; Harrison, Christopher

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James M. D. Day

D. Graham Pearson

Bruce A. Kjarsgaard

Abigail K. Barker

Nancy Joyce

David Lowry

Chiranjeeb Sarkar

Christopher Harrison


Melilitite, nephelinite, basanite, and alkali basalt, along with phonolite differentiates, form the Freemans Cove Complex (FCC) in the south-eastern extremity of Bathurst Island (Nunavut, Canada). New 40Ar/39Ar chronology indicates their emplacement between ~ 56 and ~ 54 million years ago within a localized extensional structure. Melilitites and nephelinites, along with phonolite differentiates, likely relate to the beginning and end phases of extension, whereas alkali basalts were emplaced during a main extensional episode at ~ 55 Ma. The melilitites, nephelinites, and alkali basalts show no strong evidence for significant assimilation of crust, in contrast to some phonolites. Partial melting occurred within both the garnet- and spinel-facies mantle and sampled sources with He, O, Nd, Hf, and Os isotope characteristics indicative of peridotite with two distinct components. The first, expressed in higher degree partial melts, represents a relatively depleted component (“A”; 3He/4He ~ 8 RA, εNdi ~ + 3 εHfi ~ + 7, γOsi ~ 0). The second was an enriched component (“B” 3He/4He < 3 RA, εNdi < – 1 εHfi < + 3, γOsi > + 70) sampled by the lowest degree partial melts and represents carbonate-metasomatized peridotite. Magmatism in the FCC shows that rifting extended from the Labrador Sea to Bathurst Island and reached a zenith at ~ 55 Ma, during the Eurekan orogeny. The incompatible trace-element abundances and isotopic signatures of FCC rocks indicate melt generation occurred at the base of relatively thin lithosphere at the margin of a thick craton, with no mantle plume influence. FCC melt compositions are distinct from other continental rift magmatic provinces worldwide, and their metasomatized mantle source was plausibly formed synchronously with emplacement of Cretaceous kimberlites. The FCC illustrates that the range of isotopic compositions preserved in continental rift magmas are likely to be dominated by temporal changes in the extent of partial melting, as well as by the timing and degree of metasomatism recorded in the underlying continental lithosphere.


Day, J. M. D., Pearson, D. G., Kjarsgaard, B. A., Barker, A. K., Nowell, G. M., Joyce, N., …Harrison, C. (2023). Early Eocene Arctic volcanism from carbonate-metasomatized mantle. Contributions to Mineralogy and Petrology, 178(12), 91.

Journal Article Type Article
Acceptance Date Oct 15, 2023
Online Publication Date Nov 20, 2023
Publication Date 2023
Deposit Date Nov 29, 2023
Publicly Available Date Nov 29, 2023
Journal Contributions to Mineralogy and Petrology
Print ISSN 0010-7999
Publisher Springer
Peer Reviewed Peer Reviewed
Volume 178
Issue 12
Pages 91
Keywords O–Sr–Nd–Hf–Os Isotopes, Ar–Ar geochronology, Rifting, Arctic, Eurekan
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