Trace element constraints on mantle sources during mid-Proterozoic magmatism: evidence for a link between the Gardar (South Greenland) and Abitibi (Canadian Shield) mafic rocks | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

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  Trace element constraints on mantle sources during mid-Proterozoic magmatism: evidence for a link between the Gardar (South Greenland) and Abitibi (Canadian Shield) mafic rocks

Type de publication:

Journal Article

Source:

Canadian Journal of Earth Sciences, Volume 44, Ticket 4, p.459-478 (2007)

ISBN:

0008-4077

URL:

http://rct.cnrc.ca

Mots-clés:

GEOCHEMICAL EVIDENCE

Résumé:

<p>
Trace and major element compositions of mid-Proterozoic (1.20-1.16 Ga) basaltic lava flows and dikes from the Gardar Province (South Greenland) provide evidence for two geochemically distinct magma sources. Based on distinct features of incompatible trace element ratios, such as Th/Ta, Th/Tb, or Th/Hf, they differ by the composition of their mantle source and by their partial melting trends. One mantle source is compositionally transitional between midocean ridge basalt (MORB)-type and ocean-island basalt (OIB)-type sources with relatively low Ta/Hf ratios (similar to 0.2), moderate enrichment in light rare-earth elements (LREE), and slightly positive initial epsilon(Nd) values (+2). It can be attributed to either a lithospheric mantle source or a depleted astenospheric mantle plume component that has been enriched shortly prior to eruption. The other mantle source is characterized by high Ta/Hf ratios (similar to 0.6), a more pronounced LREE enrichment, and initial epsilon(Nd) values around 0. Elevated Ce-N/Yb-N (7.0-9.8) and Tb-N/Yb-N ratios (1.6-1.8) of the rocks derived from this source indicate the presence of garnet during melting, suggesting melt generation at depths &gt; 70 km. This mantle source has the geochemical characteristics of an OIB-type source and is interpreted as originating from a mantle plume. Samples from the slightly younger (1.14 Ga) Abitibi dike swarm (Superior Province, Canada), spatially connected to the Gardar Province, show very similar trace element characteristics and the same two distinct magma sources can be identified. The geochemical similarities between the magma sources in South Greenland and Canada support the idea of a genetic link between the two magmatic provinces. This link strengthens the idea that the system was a long-lived major intracontinental rift zone.</p>

Notes:

Can. J. Earth Sci.Halama, Ralf Joron, Jean-Louis Villemant, Benoit Marki, Gregor Treuil, Michel 113 NATL RESEARCH COUNCIL CANADA-N R C RESEARCH PRESS